Concrete5 through 8.5.5 deserializes Untrusted Data. The vulnerable code is located within the controllers/single_page/dashboard/system/environment/logging.php Logging::update_logging() method. User input passed through the logFile request parameter is not properly sanitized before being used in a call to the file_exists() PHP function. This can be exploited by malicious users to inject arbitrary PHP objects into the application scope (PHP Object Injection via phar:// stream wrapper), allowing them to carry out a variety of attacks, such as executing arbitrary PHP code.

References

• https://nvd.nist.gov/vuln/detail/CVE-2021-36766
• https://hackerone.com/reports/1063039
• http://packetstormsecurity.com/files/163564/Concrete5-8.5.5-Phar-Deserialization.html
• http://seclists.org/fulldisclosure/2021/Jul/36