CVE-2021-21264: 
PHP vulnerability analysis and mitigation

CVE-2021-21264 is a security vulnerability discovered in October CMS, a free and open-source content management system based on Laravel PHP Framework. The vulnerability was disclosed on May 2, 2021, and represents a bypass of a previous security fix (CVE-2020-26231). This vulnerability affects October CMS versions 1.0.471 and 1.1.1 (GitHub Advisory).

The vulnerability allows authenticated backend users with specific permissions (cms.managepages, cms.managelayouts, or cms.manage_partials) to bypass the Twig sandbox restrictions when cms.enableSafeMode is enabled. Through this bypass, attackers can write specific Twig code that escapes the sandbox environment and execute arbitrary PHP code, even when such execution should be prevented by the safe mode setting (GitHub Advisory).

The vulnerability impacts systems where cms.enableSafeMode is enabled to restrict PHP code execution by users with CMS management permissions. Organizations relying on this safe mode feature to prevent arbitrary PHP code execution in production environments are particularly affected. The vulnerability allows privileged users to bypass these security restrictions and execute unauthorized PHP code (GitHub Advisory).

The vulnerability has been patched in October CMS versions 1.0.472 and 1.1.2. For users unable to upgrade immediately, a manual patch can be applied by implementing the fix from commit f63519f. Organizations are strongly recommended to upgrade to the patched versions to ensure system security (GitHub Advisory).