PHP Type Juggling Vulnerabilities How PHP's type comparison features lead to vulnerabilities, and how to avoid them. Well come to that in a minute. attackers the ability to bypass it ? We can clearly see it is about PHP Type Juggling since we are comparing md5 ($_GET ['secret']) with its value. So for example : If we take a look at the resource that root-me gave us, we get a pretty good idea how we are going to do this. The in_array function will compare each array element to the input (and return true) once there is a match. Introduction to PHP type juggling PHP is a loosely typed programming language. Yet again, there are two examples where this is quite obvious: You see how both of these functions are described in the PHP manual. Echo - 7/TCP/UDP. If its bigger than 0, it will assume that the user is logged in. Also you should check the Wrapper Phar:// in File Inclusion which use a PHP object injection. In this scenario, the secret string thats needed to generate the signature is only known to the server, but not to the user or an attacker. From Zero to Hero Free Learning Tutorials for HTML, CSS, Javascript, PHP, Python, C++, C#, Java and more. Let's have a look at PHP type juggling and how it might lead to authentication bypass flaws. If those checks fail, the function will deauthenticate the user, redirect him or her to /admin/login.php, and abort the remainder of the script execution. Root-me.org PHP Type juggling PHP loose comparison On this challenge we need to find a way to login. The calculated MAC (i.e. Using Content Security Policy to Secure Web Applications. September 21, 2020. But the real problem, from an attackers perspective, is that the password hash that was taken from the database is part of the MD5 hash. Bypass Constraint Language in PowerShell. Once you are. Or the same as the boolean TRUE? This means that you dont have to define the type of any variable you declare. Its value is assigned during the construction of the class, as illustrated. The theory behind this is as follows. Teclib GLPI before 9.4.1.1 is affected by a PHP type juggling vulnerability allowing bypass of authentication. So to make this check return something other than null, we first have to make sure that _get_data is returning something. To quickly spot where the function was defined, I used the Find in Folder functionality of my text editor (Sublime Text). Clicking on the highlighted number displays the actual check_login function. PHP accomplishes this by automatically casting incompatible variable types into types that allow the requested operation to take place. One of them is its inconsistent naming of built-in functions. Everything lines up perfectly so far, and having an encrypted cookie would cause a nuisance that might even result in a failed attack. You could write it as the following PHP code: The reason why apple matches 0 is that PHP tries to convert apple to an integer. Oh great! The reason involves both PHP Object Injection and even Local File Inclusion (LFI) through PHPs autoloading feature. But, since there are no (zero) leading numbers in apple, PHP will treat the string as 0. It seems like we are on the right track. These vulnerabilities can happen during comparison of PHP variables, because PHP will automatically convert the data into a common . The good news is that fixing it is straightforward. However, often this is not enough. If there is a user, it will create an MD5 hash consisting of various values. 2. PHP somehow has to convert both values to the same data type. Being able to compare strings to integers is a very convenient feature when you deal with user input, especially for beginners who arent as familiar with data types. In this case, the type of a variable is determined by the value it stores. Since its not useful for writing a reliable exploit for both Windows and Linux, we need to find another way to upload files. However, we can ignore them, due to the loose comparison of $checksum and $tmp using the == operator. Equal vs Identical It would take weeks to analyse every bit of code starting from index.php, line 1. In the world of web application security, one apparently small slip-up can compromise the entire security of your web application, even when that mistake consists of leaving out a single character. But at this point, we dont even need them. Most of them wont lead to vulnerabilities, but some of them will, under the right circumstances. Automatic Type Juggling in PHP But, in PHP, there is no need for any type of specification while PHP variable declaration. Thank you for watching the video :Authentication Bypass in PHP | PHP Type JugglingMuch like Python and Javascript, PHP is a dynamically typed language. Credential Access & Credential Dumping. The explanation is obvious once you know how its worked out. This means that variable types are checked while the program is executing. This one happens when using scientific E-notation. Since good things come in threes, three equal signs mean that the comparison should take the data type into consideration. If thats not the case, it will get its data from $_COOKIE, which holds the data from cookies sent to the server by the client requesting the page. Did you know, for example, that both of these comparisons would return true? General concept; Authentication bypass Invicti Security Corp 1000 N Lamar Blvd Suite 300 Austin, TX 78703, US. We could circumvent this restriction by uploading an .htaccess file, and force any other extension to be recognized as a PHP file, for example .pwn or (since its sometimes already registered) use .pht as the extension instead. A user can simply type the string 2 bottles into the input field, and PHP would automatically extract the integer 2 from the beginning of the string. At least one of radix character and binary exponent must be present.". More information in our Privacy Policy. If there is a hash with the same format in the database, he will be logged in as the user that the hash belongs to, without needing to know the password. There are various, subtle vulnerabilities that can arise from loose comparison. If an integer value is assigned to a variable, it becomes an integer. The check will still try to retrieve the string following the final period. As we can see, the cookie value is saved in the $private_data variable, as well as in $_SESSION. One trick for Windows is to save the file as exploit.php. instead of exploit.php. But, there is a problem. Get smarter at building your thing. Authentication Bypass It would be easy to assume that this code could be used to bypass authentication: if ($_POST ['password'] == "secretpass") Below this check we see a comment that describes what happens in this function: // using session, and-or cookie data see if we are authenticated. He explains the vulnerability details, minimum requirements, vulnerability techniques, vulnerability chaining with other vulnerabilities, recommendations, practice labs, and much more. Time to get user carl, his api_key starts with 3, and we try to send a 3 as integer in api_key field, however that is not going to work in this case as his api_key has 3 numbers until the first letter (if the key starts with a number we need to set the api_key in json to first part of numbers of the original api_key ) 399d65963db11309b2f6e4a59094686b12133274b47c867e52b277b68a0ef39b so we need to use 399 as the api_key to get access to his data. These files are uploaded via an .xml file that describes all the folders, files and content that are needed for the extension to work. For this to work, json data has to be accepted by the application. Pinterest. If you want to have an exact comparison of two values, this may lead to the undesirable results weve seen with in_array. First, it creates an instance of the LoginOperations class and then calls its get_effective_uid method to return the user ID. Another thing is that the order of common parameters varies greatly among different functions. $var, then $varis of type string. The code uses json_decode (), so we are able to specify a type other than string or array via the JSON object passed using the password GET parameter. PHP has a feature called type juggling, or type coercion. Forgetting even a single character can have a huge impact on the security of your application. the result of hash_hmac ()) is a string containing hexadecimal characters. Follow to join The Startups +8 million monthly readers & +760K followers. In this blog, we will discuss why type juggling occurs, what are the potential impacts, and why we should use strict comparisons when developing applications in PHP. However, urldecode and urlencode are named differently, for no apparent reason. Im kidding! Summary. So lets take a look what data is actually being passed by $_COOKIE. Description. Perhaps they intended to disappoint security researchers and blog readers keen to solve a nice crypto challenge? We could simply serialize an array containing any data types from boolean to integer, and feed it to unserialize. As you see, I tried to save the text hello in the file exploit.php.. However, these are not the only vulnerabilities that may arise. Did you know that a single missing character in your code can cause your authentication mechanism to be broken and give Its returned from the function get_userid. Have you ever experienced that sinking feeling when you discover that youve run out of one crucial ingredient for a special meal? If display_errors is not set to off, it can be as simple as converting a GET parameter to an array with the method described above. If you were hoping that we were going to crack some advanced encryption algorithms, Im afraid youre going to be disappointed. . Sau 1 s ln th th ti nhn thy, D ta c bypass qua c th tn ngi dng vn l user1. The first one is Auth Bypass and the second one is exploiting a custom API . However, its possible to bypass the check in Windows. Now we know that we have succeeded. This approach has various disadvantages, including being vulnerable to a length extension attack, and therefore should not be used in production in any form. Collision Based Hashing Algorithm Disclosure, Using Content Security Policy to Secure Web Applications. This approach of PHP to deal with dynamically changing value of variable is called type juggling. We have 2 users alb0z and james, in this case we cant bypass into alb0z because the hash must start with 0e in order to bypass it, but we can still log into james account. Wed either have to pass the integer 0 or boolean TRUE as $checksum to the function in order to pass the check without knowing the password, providing the hash string doesnt start with a number other than 0. There are four elements in the $values array: apple, orange, pear and grape. Therefore, it is completely user-controllable. This is why its important to know the ins and outs of the programming language of your choice, and to read the documentation regarding dangerous functionality to understand its implications. The image below shows the difference between Loose Comparisons and Strict Comparisons, Developers that are not aware of this type of attack will usually compare data through something similar to this, So in this case if the $key starts with 0e, then we can simply give a string that productes an another md5 hash which starts with 0e in the $string variable, which we may give it through GET or POST requests or other types of input, Some such string are QNKCDZO and 240610708, In the examples below I will go more into details on how to exploit it, First I wrote this simple PHP authentication mechanism which doesnt use a database so you can reproduce the attack simpler and faster, Now notice the line where the script compares the md5 hash of the password in POST request with the md5 hash of the password saved in the database (array in this case). Facebook. These hashes can detect 3 different vulnerabilities: type juggling, weak password storage and incorrect Bcrypt usage. . If afterwards an int value is assigned to $var, it will be of type int . We can have an extension with any name containing our shell. Since we now know the name of the authentication cookie, we need to look at its content. If the type differs, PHP will not attempt any conversions; it will return FALSE instead. Type Juggling PHP does not require explicit type definition in variable declaration. This could mean entering a username and password, logging in via an SSO flow, or providing a unique access key. Authorization is about checking if you have the right permissions. More details will be shown in the next example. Its important to note that administrators almost always have the user id 1. Im sure that the developers of CMSMS knew about loose comparison and its pitfalls, but just werent paying close attention at the time. For this to work, the affected classes must contain certain magic methods, like __toString that would be called on to deserialize user input, casting the deserialized object to a string, or more commonly __wakeup which will execute a specific action upon deserializing an object. This function hashes the first parameter per default as bcypt. In most cases, this is significantly easier than bruteforcing the secret value. But this kind of flexibility sometimes causes unexpected. PHP Pop Chains Achieving RCE with POP chain exploits. During the comparisons of different variables, PHP will automatically convert the data into a common, comparable type. As the API only accepts json, we need to send json through http, and Im going to do that using curl and I will check both using a valid and an invalid key. So its better to use TRUE in this case, as the comparison will always result in TRUE when its compared to a non-empty string. There are basically two data types that you can get from these variables: string and array. Ive seen this name before. Now starting to analyze the code. In cases of simple comparisons, we recommend that you use three equals symbols (===) instead of two (==). In worst cases they can lead to "Authentication Bypass" , "Account . In the circumstance of comparisons of different variable, PHP will automatically convert the data into same data type. This is referred to as type juggling. This means that variable types are checked while the program is executing. So it doesnt contain php and the check passes. Its still hard to understand why passing 0 to in_array in the above scenario will lead to a match. Loose Comparison Vulnerabilities in PHP There are various, subtle vulnerabilities that can arise from loose comparison. If afterwards an intvalue is assigned to $var, it will be of type int. Viewed 3k times . The PHP developers have made the decision to sacrifice security for convenience and ease of use. SQL injection - Authentication. Its a little different for strings and boolean values. So one of the first files I looked at in CMSMS was /admin/index.php, to find out how it checked whether a user was logged in. Why would PHP inform us, incorrectly, that there is a zero in the array? If we passed the value cherry to the function, var_dump would print bool(false) since its not found in the array. Its name is saved in the _loginkey property of the current class. Further, a variable when assigned value of different type, its type too changes. Comparing strings to numbers like that makes coding a lot easier, especially for beginners, but it also leads to the mysterious in_array behaviour. And I wrote this simple python script to do the brute forcing for us. And if you knew the password you wouldnt have to hack anything. You dont need to be a web security expert to be able to use the === operator on critical comparisons. So today Im going to explain these attacks, how to exploit them, and how to avoid them. After that, it checks whether any array keys are missing. But we cant depend on this being the case for every server, and .htaccess files are often disabled. This means that we would compare the string 0 to the string secretpass. So, in order to compare it, PHP has to convert the data to the same type. But this is exactly what makes this type of vulnerability so dangerous. Then, delete Carlos. By using this website you agree with our use of cookies to improve its performance and enhance your experience. This means that during the comparison of variables of different types, PHP will first convert them to a common, comparable type. There are still several problems with this check. How to bypass PHP strings == comparison for sha256 string? Simply add a single character. This makes sure that the type is taken into consideration when comparing the values. Professional investigator of nerdy stuff. When using the == operator, PHP attempts something called loose comparison (or type juggling). The logic for that is in _get_data(), as illustrated. (There are special cases where PHP will still convert strings to integers, but we will talk about this in the next section.). It might be a single ingredient, but it ruins the whole dish, doesnt it? With loose comparison, its possible for a PHP developer to compare values even if they have a different data type, such as integers and strings. . Since the metasploit framework is perfect for this kind of automated exploit, I have written a module for it. Lets look at the code again. Of course, this is also a problem in databases with lots of users. Objective -> This lab uses a serialization-based session mechanism and is vulnerable to authentication bypass as a result. While in_array takes data to search as the first parameter, strpos takes it as the second one. In order to get rid of the error, we have to pass a cookie named _sk_ with any string we want (for example the string pwned). m nhim c ca ta l phi ly c password ca admin kia. I'll put two links worth reading concerning this exploit. It first tries to retrieve the user id with the get_userid function. However, there is a problem. This article explains the CMSMS vulnerability, which is a perfect illustration of why you should pay very close attention when you code your web application, especially critical parts such as authentication functionality. This will be our method of uploading a PHP file containing malicious code. As james api_key starts with a letter, we can use 0 as api_key to get his data. Notice the additional . at the end of the first variation. This article provides an introduction to PHP Type Juggling Vulnerabilities and loosely typed code and type comparisons, and how to avoid or fix them. Invicti Security Corp 1000 N Lamar Blvd Suite 300 Austin, TX 78703, US. Now that we are logged in, we can perform any administrative action we want. Yet again, we have proof that in certain circumstances, a small information leak can have a huge impact. Lets take a look at the filter. To see whats wrong with that, take a quick look at the PHP manual. The string test doesnt begin with a number. When you use parameters that come from json_decode() or unserialize(), its possible to specify whether you want to pass your number as an integer or a string. Often these signatures are generated as illustrated in the PHP code, even though this does not conform to the RFC 2104s recommended way to create HMACs. It seems that one of my favorite UNIX quotes applies to PHP as well: Unix will give you enough rope to shoot yourself in the foot. So basically what this script does is accept json data and return some secret data for the user. An interesting point to note from the loose comparison chart . Close. If this check has already taken place, the _data property of this class instance will return its content. And thats just the tip of the iceberg. In this episode, we will learn about how the type of juggling can be exploited to bypass authentication. FTP - 21. . Creates god awful infographics. WP Magic Link Login 1.5.4 - Passwordless Authentication WordPress Plugin . Instead, it will call the method _get_data which seems to return an array and check the value of an array element against the eff_uid key. There is a lot to keep in mind and a lot more to mess up. It means that when you define a variable, you don't need to declare a type for it. With our plugin, you can. Youll see why when you look at the _decrypt and _encrypt methods. Below you can see _check_passhash: This looks very promising. The root issue here is the way PHP type juggles when comparing values with the double equal operator. Dynamic typing allows developers to be more flexible when using PHP. Since both are already of the same type, PHP does not need to convert anything, and therefore the comparison will result in false. Edited on Wed 09 October 2019 TL;DR: Magic hashes are well known specific hashes used to exploit Type Juggling attacks in PHP. __destruct() when an object is deleted. PHP may attempt to convert the type of a value to another automatically In order to pivot into an internal network or steal sensitive data, we actually need a proper shell. To solve this machine, refer the blog from the below link to exploit it using the PHP Type Juggling. Before doing the comparison the string is casted to boolean so it ends up as true == true which is a truthy statement. How PHP compares values PHP has a feature called "type juggling", or "type. This is a relatively easy way to deal with PHPs often confusing behaviour when it comes to type comparisons. Just from looking at the code, you know that there is no 0, and therefore youd expect the search to return false. To solve the lab, edit the serialized object in the session cookie to access the administrator account. The == part is the operator that is being used for a loose comparison. For MD5, the strings 240610708 and QNKCDZO can be used: Its relatively easy to fix Type Juggling vulnerabilities most of the time. In most cases, it doesnt take a long time to search for the == operator in your code and replace it where you need to. Diving into unserialize() How PHP's unserialize() works, and why it leads to vulnerabilities. PHP always tries to convert a string to boolean if both are compared. This will make pwned our CSRF token value. PHP - type juggling 30 Points PHP loose comparison Author vic , 10 March 2016 Level Validations 7572 Challengers 3% Note 1 2 3 4 5 330 Votes To reach this part of the site please login 4 Solutions Display solutions Submit a solution You should validate this challenge first Challenge Results 0 10 20 30 40 50 60 70 80 . Type Juggling in PHP Description When performing operations or comparisons between two different types of data, PHP will attempt to convert one to the same type as the other. . If you didnt think rope would do that, you should have read the man page. Nh vy bypass on code trn ta xy dng payload sau: . PHPMagicTricks-TypeJuggling.pdf - Free download as PDF File (.pdf), Text File (.txt) or read online for free. After a while it returned the following result. This occurs in Auth . If the values compared begin with "0e" or "00e", etc, they will be juggled to a float and compared as . However, this file would no longer be recognized (at least in Linux) as a PHP file, because the extension is missing. Today, let's dive into PHP type juggling, and how they lead to authentication bypass vulnerabilities. All we have to do is add square brackets after the parameter name: mact[]. Authentication is required to access the features of the application using a set of . The only variable in __FILE__ that is unknown to an attacker is the path to the webroot. As you see, there are almost two thousand files in CMSMS. The only problem is that we still need to find a payload that will ensure that we pass the password hashsum check. We develop LChecker, a system to statically detect PHP loose comparison bugs. Im not sure if this hash is in place in order to avoid the problem of having the same login key for different installations or versions of CMSMS, but its values can easily be guessed and some of them are even static. Consider the following PHP code, which can be used to find a value in an array. Of course, there is nothing wrong with that. CMSMS has a lot of modules that can extend the functionality of the CMS. Finally, we recommend that you avoid casting the strings to the same type, before comparing them, as this often has the same effect as the == operator. I don't know if there's a way of type juggling from the URI. There was a cookie that could be decoded, edited and then encoded again and it worked, but this is a different scenario. Synacktiv discovered that the GLPI Remember me feature does not implement strong PHP comparisons and can thus be abused to authenticate as any user . Then it will generate the password hash, by hashing different values including the received password hash from the database, and save it in $tmp. I have mentioned a special case in the Authentication Bypass section where two strings are converted to an integer when using loose comparison. Among those values, we also have the current user agent and the IP address, which aims to prevent session token theft. The latter would work by passing a query such as ?array[]=first_element&array[]=second_element. PHP is often referred to as a loosely typed programming language. To see what it does, we have to go further down the rabbit hole. In PHP, this means that it is equal to the integer 0, which explains why the comparison returns true. But, by far, this is not the only problem you can encounter when dealing with PHP! 32. If we send a base64-encoded, serialized array that was passed through str_rot13 in a cookie (whose name is an MD5 generated by the full path to class.LoginOperations.php, the string CMSMS\LoginOperations and the current version number), we can control the $private_data variable. In this case, the type of a variable is determined by the value it stores. This, however, leads to a variety of problems and might even cause security vulnerabilities, as described in this blog post. Local File Inclusions that are caused by unserialize in combination with an existing autoloading functionality are almost exclusively restricted to files ending in .php. 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And when run, it finds the numbers for us. It turns out that this is the name of the CSRF token parameter. We also enhance the PHP interpreter to help dynamically validate the detected bugs. Hashes that start with 0e are called magic hashes and you can find many types of them here https://github.com/spaze/hashes, These type of bugs are probably the easiest ones to fix, one needs to use strict comparisons instead of loose comparisons, A place where I will share things that might help others, Will do my best to keep adding new content regularly, // In a real world environment this would be in a database, // Check if user has given a correct password (This is where the bug is), // A real world app would redirect us to the main page and set cookies, but for testing purposes I'm going to leave with just a message, "Content-Type: application/json; charset=UTF-8", '7c2fceb815553c50fa1c2e3fe4a108fc71d966b199f660ed048c32dfe5978aff', 'This is secret and only alb0z should be able to access it', 'e682a16f3973fa12ecf221baa5b1e169157c44ef301180077fe48eae69fb7594', 'This is secret and only james should be able to access it', '399d65963db11309b2f6e4a59094686b12133274b47c867e52b277b68a0ef39b', 'This is secret and only carl should be able to access it', // get any input sent to us and json decode it, // check if username and api_key are in json data we received, // Check if the given api_key is valid for the given user, // if everything is okay, then print secret data, #brute force which api_key integers will work, "Data for user: %s with %i as api_key: %s". Services. Array elements in $_GET, $_POST or $_COOKIE are always either strings or arrays, never integers. However, this is not yet the case. 2- Type Juggling. So it doesnt really matter which numbers follow after 0e, it will always result in the number 0. To determine whether the value apple is among them, we pass it to in_array. One of the areas where critical mistakes often happen is in the authentication functionality of a website. This function hashes the first parameter per default as bcypt. To know the hash, you need to know the password. Note: If the application accepts json then we can bypass all the hashes and not only the ones starting with 0e, thats because HTTP sends all the data in string format, but with json we can send integers too. The title gives us a easy tip on how we need to abuse this. CMS Made Simple (CMSMS) is a Content Management System (CMS) written in PHP, and subject to all the beautiful pitfalls that make PHP so unique. This becomes apparent when you look at the functions that are responsible for encoding and decoding data. data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAKAAAAB4CAYAAAB1ovlvAAAAAXNSR0IArs4c6QAAAnpJREFUeF7t17Fpw1AARdFv7WJN4EVcawrPJZeeR3u4kiGQkCYJaXxBHLUSPHT/AaHTvu . This is exactly what happened in CMS Made Simple (CMSMS): one missing character was sufficient to result in an Authentication Bypass, and ultimately Remote Code Execution (RCE). There are lots of reasons not to like PHP. tj gr jx ku oo . It will be appended to the message thats being sent to the server, and is used as a signature. Instead, developers should use PHPs built-in hash_hmac function to generate this kind of signature: The general idea behind this is that shell_exec will only succeed if the attacker knows the secret value. Again Im going to write/use a simple script without a database which will act like a real world API. Authentication. Since both the $uid and $checksum variable we see above come from the deserialized array in the cookie, we can give $private_data[uid] the value of an integer of 1, and $private_data[cksum] can be set to the boolean TRUE. Last week I was reading about PHP Type Juggling vulnerabilities and I decided to spend a couple of days learning about them. Im using curl to send POST requests, but the same thing can be achieved through your browser. CMSMS didnt contain any obviously dangerous gadgets. The reason why this is the desired format is that 0*10n is always 0. First confirm that the strings hash gives us the desired hash, and then make the POST request using curl. TIL ( "0e1" == 0 ) is true in PHP due to type juggling, and this can cause Authentication Bypass vulnerabilities, like CVE-2020-8547 in phpList. In the case above, it will cast the integer literal 1 into a string, meaning that it can be concatenated onto the preceding string literal. After conversion, the comparison looks like this to PHP: This kind of behaviour is called an implicit type conversion or type juggling. However, there is one thing you need to know about PHP input when it comes to $_GET, $_POST and $_COOKIE. Our researcher, Sven Morgenroth, explains how he found an Authentication Bypass in CMS Made Simple, what PHP Type Juggling is, and why you should never use the unserialize function together with user-supplied input. != is the opposite of == but it still is a loose comparison, so it is still vulnerable. Hello! This means that even if there is a string beginning with (or solely consisting of) 0, it will still fail the comparison when the other value is the integer 0. Lets first take a look at the user ID. One way to avoid this is to use the === and !== operators for comparisons, this will check the type as well as the value and no implicit casting will be done. Various code execution CVE numbers were assigned due to this function. Using this format, an attacker can try to log into every single user account with a password that will result in a hash of the mentioned format. So lets byrypt the value admin" and provide it to our statement. Hacks and secures. I think that with a MAC, for instance "ff6d0.5885d", the PHP juggling will be compared to int (6 . Unserialize is infamous for its issues with memory management. The behavior I have just described is obviously undesirable in the many instances in which you want to have an exact comparison of two given values. Anyway, str_rot13 and base64 are not the only functions within the two methods. Bug #3: Wordpress Authentication Bypass Publicised by MWR Information Security (again) November 2014 Fun and interesting attack, but limited practicality . PHP is easy until you come across the variable types and context in which the variable is used. The function var_dump prints bool(true) as result of this search, since apple is indeed a part of the $values array. PHP Type Juggling Examples. In this case, a tester has to register with a password that results in a hash, in the scientific E-notation format. Active Directory Authentication. Let's walk through the exploitation process: 1. AWS. gp. PHP will convert string to integer. It does this by treating strings with any given content as TRUE. As you can see in the middle, the function was called check_login. So even if we dont know the value of $tmp, we can pass the check simply by using TRUE. If you dont pay close attention, you end up introducing a flaw that is so easy to exploit, its like taking candy from a baby. Or maybe exploit your API to get valuable information, or bypass your CSRF protection, or in some cases even gain RCE. If we go back to the in_array function, there is an optional third parameter, which is set to false by default: The name of the parameter is $strict, and when it is set to true, PHP will take the datatype of the values into consideration when comparing them. This is because the input is filtered and any file with an extension beginning or ending with php will be rejected. Think of this analogy: comparing strings to integers would be like saying The sky is exactly as blue as happiness, which makes no sense at all. This means that we can easily find the right cookie name, just by trying different webroots and versions. The only drawback is that this behaviour doesnt work in Linux. This is problematic because usually hashes, like md5 in our example, are written in hexadecimal encoding, which consists of the numbers 0-9 and the letters a-f. After enough attempts, you can therefore generate a string that begins with 0e and is followed by numbers only. Even though this approach allows inexperienced users to code a website in PHP, it makes it much harder for them to keep it secure. Its also possible to check whether or not a specific hashing algorithm is present when loose comparison is used, similar to the Collision Based Hashing Algorithm Disclosure. Type Juggling Authentication Bypass Vulnerability in CMS Made Simple Sven Morgenroth - Mon, 09 Jul 2018 - Our researcher, Sven Morgenroth, explains how he found an Authentication Bypass in CMS Made Simple, what PHP Type Juggling is, and why you should never use the unserialize function together with user-supplied input. sr. tx ce wt rm mr tv. 3. This means that variable types. It receives the data from a cookie. However, those memory issues are difficult to find, let alone exploit, on different platforms. Modified 2 years ago. . By employing .php. as the extension, we bypass the filter but still have a valid php extension. __wakeup() when an object is unserialized. Its pretty obvious what should happen when we pass the number 0 to the array. As seen before in the example with five bottles, PHP tries to extract a number from the beginning of the string, converts it to an integer, and then compares this to the integer we passed for comparison. PHP Cache; PHP HTTP Authentication; PHP WebSockets; PHP Built in server; PHP Common Errors; PHP Password Hashing Functions; So it was important to set some priorities and create a plan for where to start. For example, the constant __CLASS__ never changes, and the CMS version can be guessed, as well as the content of __FILE__. Banner Grabbing. It will throw an error in a function that expects a string value, and will display the full path of the file in an error message. Any idea how to bypass the auth check? If the value does not exist, it will just return the result of calling the method get_loggedin_uid. In this example Im going to show you how to exploit the vulnerability even when the hashes dont start with 0e. Since weve already found an issue with strpos, lets see if we can also find one for in_array. The same goes for !=, which should be avoided in favor of !==. This section contains an explanation of some of the more common ones. Weve come so far, but to authenticate, we still need the correct password. A good way to find some vulnerable code in a short amount of time is to concentrate your efforts on critical functions and functionality that is easy to get wrong. For one, there is base64_decode or base64_encode with underscores in the function name. Lets take a closer look at this method before we come back to $_COOKIE[$this->_loginkey]. The code uses a loose comparison when comparing the supplied 'm' variable with an influenced string value. Internally, PHP will determine the type by the context in which you use the variable. When you forget this, its easy to make mistakes and write a strpos check thats almost never true. As Ive mentioned, CMS Made Simple is written in PHP, and the loose comparison operator is quite popular in this language. qk co nh tn ag sp by nd lu. Also, PHP Object Injection requires existing code (gadgets) that can lead to dangerous actions. An HMAC is often used as an additional security measure when deserializing input, for example, from cookies, since the dangerous unserialize function can only be called if the message was not tampered with by an unauthorized party. Thats depressing, right? PHP - Type juggling: 1 November 2022 at 23:27: JakeRansom PHP - Type juggling: 1 November 2022 at 22:08: Pmorgan PHP - Type juggling: 31 October 2022 at 19:15: Craizox PHP - Type juggling: 31 October 2022 at 13:54: moonlight PHP - Type juggling: 31 October 2022 at 09:26: hblg PHP - Type juggling: 31 October 2022 at 05:21: tho PHP - Type . Page Topic: PHP Type Juggling. Type Juggling PHP will do just about anything to match with a loose comparison (==) Things can be equal (==) or really equal (===) Implicit int parsing strings is the root cause of a lot of issues We should first understand how php loose comparison works, Here is a link for you PHPMagicTricks-TypeJuggling.pdf. This seems like a big problem. The search further told me that the function was defined in lib/page.functions.php, which could be opened in Sublime by double-clicking the highlighted line number on the left. In their comment, they actually acknowledged the fact that this function has nothing to do with encryption, but rather with encoding, which is why Im still puzzled as to why they called it _encrypt. We even get access to the source code. For this reason, PHP also has the === operator. If an integer value is assigned to a variable, it becomes an integer. It employs a context-sensitive inter-procedural data-flow analysis together with several new techniques. A very important note here is how the exponent works. I prefer you first go through the below write-up to understand better. PHP often known as a 'loosely typed' programming language If we recall in PHP, no data types in any variable have to define. When you are auditing a popular, well-established web application, you are dealing with thousands of lines of code. Dont lose hope yet! CVE-2020-8088 - UseBB Forum 1.0.12 - PHP Type Juggling vulnerability. We have 3 users on the API database (array in this case) alb0z,james and carl, and all three of them have private api keys 64 characters long. After they are deserialized, the data types are the same as in the original array. When searching for the code that defines the secure param name, we end up in the file lib/include.php. Most of them are user-controllable or static. For example, if you assign a string to a variable, its type will be the string: Type Juggling PHP does not require explicit type definition in variable declaration. A binary exponent consists of a 'P' or 'p', followed by an optional plus or minus sign, followed by a nonempty sequence of decimal digits, and indicates multiplication by a power of 2. Type juggling means dealing with a variable type. Windows, on the other hand, does us a huge favor. It tells us not to pass untrusted user input to unserialize. If a string value is assigned to the variable, it becomes a String. This section contains an explanation of some of the more common ones. After a quick search in the same file, this was the function. . First sending a normal request with an invalid password to confirm that we cant simply login with a random password, And now lets try it with a string which produces a md5 hash that start with 0e in this case Im going to use NWWKITQ. After that, it will check if $ext begins or ends with the string php. In a real world app the API could do anything from returning personal user information to sending messages, deleting posts or purchasing products in an e-commerce. This can therefore significantly reduce the number of attempts that an attacker needs to bruteforce a valid signature. Since we have set the $checksum variable to TRUE, the comparison is basically like this: TRUE == '9ab50f27d4201db9b28483ba83c48ebafbb2aa17'. Below you can see it in action. Cloud Security. In the video below you can see a presentation about PHP Type Juggling on the Security Weekly show. Page Topic: PHP Type Juggling. It turns out that the reason is actually quite simple and sometimes even exploitable as well see later. yf. However, if we created a cookie and tried to log in, wed still have one tiny problem. This is easier said than done. For example test == TRUE, while an empty string is always treated as FALSE. This means that during the comparison of variables of different types, PHP will first convert them to a common, comparable type. Linkedin. Scientific E-notation is used to write very long numbers in a short form. em. It was as easy as searching for function check_login(. This is from a HTB machine called Ransom. It is derived from "loose comparison" (denoted with ==): As one could determine from the comparison charts, "strict" comparison requires a value to be exactly accurate, whereas loose comparison allows for some wiggle room. pm. That is exactly what happened with CMS Made Simple, and Ill explain how I found and exploited this vulnerability. 01:12 What is Type Juggling04:16 PHP Type Comparision05:36 Example06:36 Null Condition07:45 DemoABOUT OUR CHANNELCyber Security is a non-profit initiative taken by security professionals. The checksum from the cookie and the generated checksum containing the database password are compared using loose comparison. We talked about why developers use weak type comparisons, how to avoid them and highlight a few of the unexpected results of PHP Type Juggling. Type juggling is a feature within PHP which provides developers some flexibility in comparing variables. Azure. Yet again, the actual check doesnt happen in this method. Therefore, this would pass the check: Instead of 0, you can even pass true, as (any_string == true) will always succeed. More information in our Privacy Policy. Fortunately, the function responsible for this wasnt that difficult to spot. The type of $token is string, since it is a Base64-encoded value. The specific flaw exists in the 'confirm.php' script when updating a members email address. To see why, look at the commands I issued. One of the past challenges was solved with type juggling, but that was a different scenario. First I wrote this simple PHP authentication mechanism which doesn't use a database so you can reproduce the attack simpler and faster Type Juggling (also known as Type Confusion) vulnerabilities are a class of vulnerability wherein an object is initialized or accessed as the incorrect type, allowing an attacker to potentially bypass authentication or undermine the type safety of an application, possibly leading to arbitrary code execution. In PHP a value starting with 0e and followed by numbers is considered as a float, and some MD5 (value) will also result in 0e [0-9] {30}. By using this website you agree with our use of cookies to improve its performance and enhance your experience. If a. Next, it checks whether or not the Cross-site Request Forgery (CSRF) token is correct. In PHP, a variable type is a context in which it is used. What happens now is that CMSMS will load the userdata of the user with the id 1 and save it in $oneuser. The function password_verify is using the php function password_hash . Authentication Bypass Ta c on m PHP xc thc nh sau: if ($_SERVER['REQUEST_METHOD'] == 'POST'){ $data = json_decode(file_get_contents("php://input")); if($data->{'username'} == "admin" && $data->{'password'} == "admin"){ echo "success"; header('location: admin'); } else{ echo "failed"; header("location: login"); } } The real problem arises when it is used on critical comparisons such as password hashes. What the in_array function does is compare the supplied value with every value in the array until it either finds a matching value (and returns true), or until all the values are compared without a match (and returns false). Unfortunately, writing web applications is not always easy. There are another two: unserialize and serialize. The number 1,000,000, for example, would be written as 1e6. Whether or not this was a food metaphor is left to the judgement of the reader. If you recall the comparisons mentioned at the beginning of this post, you may remember that comparing boolean TRUE to any string will alway return true. This makes it possible to compare the number 12 to the string 12 or check whether or not a string is empty by using a comparison like $string == True. In PHP, a variable type is a context in which it is used. Even though we can upload any file using the file manager, we cant upload files with the .php extension. . 127. The search for the get_effective_uid method leads us to a file with the following path: lib/classes/internal/class.LoginOperations.php. Now its time to exploit it. It calls all the other functions that check whether or not the visitor is authenticated. Now in this we will look at a sample php code that is vulnerable to PHP Type Juggling. But why would this deliver the weird result in the comparisons example? It therefore doesnt come as any surprise that it is used on multiple occasions throughout the code. Type juggling authentication bypass in GLPI <= 9.4.1.1 CVE-2019-10231 Security advisory 2019-04-23 . Hello readers, in this blog post, our consultant Aditya has discussed the PHP Object Injection vulnerability. They also need to have controllable properties and call exploitable functions. Lets continue to get other users data. There exist a few pages that are directly accessible by any unauthorized user, e.g., logout.php and login.php. In PHP there are 2 main comparison methods called loose and strict comparisons, Loose Comparison (==) - Doesnt check the type of the given data, Strict Comparison (===) - Does check the type of the given data, This kind of vulnerability lies on Loose Comparisons, and it happens because loose comparisons dont check the type of the data and will return TRUE if a string is compared to 0. Type juggling means dealing with a variable type. This is yet another example of why you really should read the PHP documentation (as if there werent enough reasons already). Youd simply log in. This result is unexpected and it doesnt make any sense at a first glance. Imagine a form that allows you to record how many bottles of water you drank throughout the day. When we look at the very next comment in the _get_data function, we see this beautiful statement: // if we get here, the user is authenticated. Twitter. If he is able to log in with a different password that also results in a hash with the same format, he knows that the site uses loose comparison and the respective hashing algorithm. That means we can add random characters to our message and always pass the signature 0e123 to the server. The value is just the string _sk_. Combined with bcrypt limitations, we propose the concept of Super Magic Hashes. It is assigned by retrieving the cookie with the name stored in the constant CMS_SECURE_PARAM_NAME. Example 1: Authentication Bypass. Here we are uploading a series of videos to learn and get expertise in various domains of security. However, even if we dont achieve a full path disclosure, the value can simply be guessed in most cases. Things are going to get a little confusing at this point. Eventually the message hashed with the secret value will result in the format ^0e\d+$, and PHP will convert both strings to 0 and pass the check. This will take the text after the last . character and save it in $ext. 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