CVE-2021-21264 : Exploit Details and Defense Strategies

This article provides detailed information about CVE-2021-21264, which involves a bypass of a fix for CVE-2020-26231 in October, a self-hosted CMS platform.

Understanding CVE-2021-21264

CVE-2021-21264 is a vulnerability that allows an authenticated backend user to bypass security measures and execute arbitrary PHP code by escaping the Twig sandbox in October CMS.

What is CVE-2021-21264?

October CMS, a Laravel-based platform, is susceptible to a security bypass that enables unauthorized execution of PHP code by authenticated backend users with specific permissions.

The Impact of CVE-2021-21264

The vulnerability poses a medium-severity risk, with a CVSS base score of 5.2. An attacker could execute arbitrary PHP code by exploiting this issue.

Technical Details of CVE-2021-21264

The following technical details outline the vulnerability and its impact.

Vulnerability Description

A bypass of the CVE-2020-26231 fix in October CMS allows authorized users to escape the Twig sandbox, leading to the execution of arbitrary PHP code.

Affected Systems and Versions

Versions 1.0.471 and 1.1.1 of October CMS are affected by this vulnerability, requiring immediate attention.

Exploitation Mechanism

By leveraging specific Twig code, authenticated users with

cms.manage_pages

,

cms.manage_layouts

, or

cms.manage_partials

permissions can bypass security measures and execute PHP code.

Mitigation and Prevention

Protecting your system from CVE-2021-21264 involves taking immediate steps and adopting long-term security practices.

Immediate Steps to Take

Apply the patch provided in Build 472 (v1.0.472) or upgrade to v1.1.2 to mitigate the vulnerability. Alternatively, manual installation of the workaround is recommended.

Long-Term Security Practices

To enhance security, ensure that users with critical permissions do not have access to write and execute arbitrary PHP code within the CMS.

Patching and Updates

Regularly update October CMS to the latest patched versions to prevent exploitation of known vulnerabilities.