CVE-2022-39261 in Twig
Summary
by MITRE • 09/28/2022
Twig is a template language for PHP. Versions 1.x prior to 1.44.7, 2.x prior to 2.15.3, and 3.x prior to 3.4.3 encounter an issue when the filesystem loader loads templates for which the name is a user input. It is possible to use the `source` or `include` statement to read arbitrary files from outside the templates' directory when using a namespace like `@somewhere/../some.file`. In such a case, validation is bypassed. Versions 1.44.7, 2.15.3, and 3.4.3 contain a fix for validation of such template names. There are no known workarounds aside from upgrading.
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Analysis
by VulDB Data Team • 09/28/2022
The vulnerability identified as CVE-2022-39261 affects the Twig template engine for PHP, a widely used component in web applications for generating dynamic content. This issue stems from inadequate validation of template names when utilizing the filesystem loader, creating a path traversal condition that allows attackers to access files outside the intended template directory. The vulnerability specifically impacts versions prior to 1.44.7 for the 1.x branch, 2.15.3 for the 2.x branch, and 3.4.3 for the 3.x branch, representing a significant security risk for applications relying on Twig for template rendering.
The technical flaw manifests through the improper handling of template names containing directory traversal sequences such as `@somewhere/../some.file` within the filesystem loader implementation. When Twig processes template names that include these sequences, the validation mechanism fails to properly sanitize or reject potentially malicious input, allowing the template engine to resolve paths that extend beyond the designated template directories. This occurs because the loader does not adequately verify that template names remain within the intended namespace boundaries, creating an opportunity for attackers to exploit the template system to read arbitrary files from the server's filesystem.
The operational impact of this vulnerability is substantial as it enables attackers to potentially access sensitive files including configuration files, database credentials, application source code, and other confidential data stored outside the template directory. This path traversal vulnerability can be exploited through user-controllable template names, meaning that if an application allows user input to influence template selection or naming, an attacker could leverage this to gain unauthorized access to system resources. The vulnerability essentially undermines the security boundaries established by the template system's intended namespace isolation, potentially leading to complete system compromise if sensitive files are accessible through the template loading mechanism.
Organizations affected by this vulnerability should prioritize upgrading to the patched versions mentioned in the advisory, as no effective workarounds exist for the issue. The fix implemented in versions 1.44.7, 2.15.3, and 3.4.3 addresses the validation logic to properly sanitize template names and prevent directory traversal attempts. Security teams should conduct comprehensive vulnerability assessments to identify applications using affected Twig versions and ensure proper patch management procedures are in place. This vulnerability aligns with CWE-22 Path Traversal and falls under ATT&CK technique T1213 Data from Information Repositories, highlighting the critical nature of protecting template loading mechanisms from malicious input that could lead to unauthorized data access and system compromise.