CVE-2021-36766 in concrete5
Summary
by MITRE • 07/30/2021
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.
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Analysis
by VulDB Data Team • 08/05/2021
The vulnerability CVE-2021-36766 represents a critical security flaw in Concrete5 content management system versions through 8.5.5, specifically within the logging configuration functionality. This issue falls under the category of insecure deserialization as classified by CWE-502, where the application processes untrusted data without proper validation or sanitization. The vulnerability manifests in the Logging::update_logging() method located in the controllers/single_page/dashboard/system/environment/logging.php file, making it accessible through the web interface's logging configuration page.
The technical exploitation occurs when user-provided input from the logFile request parameter is directly passed to the file_exists() PHP function without adequate sanitization. This oversight creates a dangerous attack vector that leverages PHP's phar:// stream wrapper functionality, enabling attackers to inject malicious PHP objects into the application scope. The vulnerability essentially allows for PHP object injection attacks that can be escalated to arbitrary code execution, as the application fails to properly validate or escape user input before processing it in a context that supports object deserialization.
From an operational perspective, this vulnerability presents a severe risk to Concrete5 installations, as it enables attackers to execute arbitrary code on the affected systems. The attack surface is particularly concerning because it operates through the web interface, making it accessible to authenticated users who can manipulate logging configurations. The exploitation chain typically involves crafting a malicious phar archive that contains serialized PHP objects, which are then loaded through the vulnerable file_exists() call, ultimately leading to code execution with the privileges of the web server process. This could result in complete system compromise, data exfiltration, or further lateral movement within the network infrastructure.
Security mitigations for CVE-2021-36766 should prioritize immediate patching of Concrete5 installations to versions that address this vulnerability, as the vendor has released updates to resolve the insecure deserialization issue. Organizations should implement additional defensive measures including input validation and sanitization of all user-provided parameters, particularly those used in file system operations. Network segmentation and access controls should be enforced to limit exposure of the logging configuration interface to only authorized personnel. The ATT&CK framework categorizes this vulnerability under T1548.002 for abuse of cloud compute infrastructure and T1059.007 for command and scripting interpreter for PHP, emphasizing the need for comprehensive monitoring and detection capabilities. Organizations should also consider implementing web application firewalls and runtime application self-protection mechanisms to detect and prevent exploitation attempts. Regular security assessments and code reviews focusing on deserialization practices are essential to prevent similar vulnerabilities in other components of the application stack.