![]() At that time, Unit 42 researchers published a blog on this vBulletin vulnerability, analyzing its root cause and the exploit we found in the wild. The User is informed that they may oppose the deposit and/or consultation of cookies using their browser’s settings prior to their deposit and one by one.Įach browser’s settings are different, the User can find the steps to follow to manage cookies in the Help section of their browser.In September 2019, a remote code execution (RCE) vulnerability identified as CVE-2019-16759 was disclosed for vBulletin, a popular forum software. The User interface customization cookie is valid for 12 months starting from its initial deposit on the User’s terminal.The audience-measuring cookie (Google Analytics) is valid for 12 months starting from its initial deposit on the User’s terminal.A User interface customization cookie that allows for the language chosen by the User by clicking the appropriate flag (French or English) to be remembered.An audience-measuring cookie (Google Analytics) which allows it to analyze the User’s browsing and measure the audience of the Site (number of visits, number of pages seen, visitors’ activity on the Site, frequency of return visits on the Site).Two types of Cookies are deposited and/or read from the Site: This information is sometimes hosted on the computer in a simple text file the server then accesses to read and write information. ![]() It contains several data points: the name of the server which deposited it, a unique ID number, possibly an expiry date. If we deserialize this payload:Ī cookie is a piece of information deposited on a web user’s hard drive by the server of the website they are browsing. We want to include packages/googlelogin/vendor/autoload.php, which contains the autoloader for Monolog classes. However, the important part is that the deserialisation process does not crash, it keeps going. The object is pretty useless for an attacker, as you cannot access its attributes or call its methods. It will return an instance of _PHP_Incomplete_Class instead. Now, when it comes to loading classes, unserialize() has a quirk: if you deserialize an object whose class name is not found (even after running the autoloaders), the function will not raise an exception or fail, as we'd expect it to. Sadly, although the file inclusion would work, the code would eventually crash, as the A_B_C class does not exist. For instance, running new A_B_C() would force the autoloader to include a/b/c.php. The vBulletin autoloader has an interesting property: given a classname, it can include any PHP file in the project tree. The class is now defined, and PHP can instanciate it. Consequently, it calls every classloader, including vB::autoload(), which generates the name of the file that contains the class, vb/datamanager/user.php, and loads said file. The computed filepath is then included 4.Īs an example, the first time vBulletin instanciates vB_DataManager_User, the class is unknown to PHP. The last segment defines the name of the file 3. ![]() The first segment is used to determine the base directory 1, while the others are simply used as directory names 2. ![]() In essence, the autoloader takes a classname, converts it to lowercase, and then splits it in _-delimited segments. Class vB_DataManager_User extends vB_DataManager ![]()
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