Jinja is a widely used extensible templating engine. Unfortunately, prior to version 3.1.5, a vulnerability (CVE-2024-56326) was discovered which allows an attacker with control over the content of a template to execute arbitrary Python code. Applications that execute untrusted templates may be impacted by this vulnerability. The issue lies in how the Jinja sandboxed environment detects calls to str.format method.

Exploit Details

Jinja's sandboxed environment aims to prevent the execution of potentially harmful code by catching calls to str.format. However, a security oversight in the sandbox environment allows for indirect calls to str.format through custom filters, which may lead to arbitrary code execution. An attacker could store a reference to a malicious string's format method and then pass that reference to a filter that calls the method.

To successfully exploit this vulnerability, an attacker needs to control the content of a Jinja template. The risk associated with this vulnerability depends on the specific application using Jinja and its exposure to untrusted templates.

Here's a code snippet illustrating the vulnerability

{% set malicious_string = "{.__class__.__bases__[].__subclasses__()[40](\"/tmp/malicious_file\")}" %}
{% set ref = malicious_string.format %}
{% my_filter ref %}  # This custom filter could enable attackers to call the malicious string's format method indirectly.

Mitigation

This vulnerability has been fixed in Jinja version 3.1.5. Developers are encouraged to update to the latest Jinja version to eliminate the security risk associated with this vulnerability. The fix ensures that indirect calls to str.format are also caught by Jinja's sandbox environment.

1. Jinja Vulnerability Report: CVE-2024-56326
2. Jinja GitHub Repository: Vulnerability Fix (3.1.5)

Jinja Security Announcement: [Arbitrary Code Execution in Templates]()

4. Jinja Documentation: Sandboxed Environment

Conclusion

The CVE-2024-56326 vulnerability in Jinja templating engine has demonstrated the importance of continuously improving the security of widely-used software components. Applications using Jinja should ensure they utilize the most recent version (3.1.5) to prevent potential exploitation from attackers able to control the content of a template. Regularly updating software components not only provides security fixes, but also ensures overall system reliability and efficiency.

Timeline

Published on: 12/23/2024 16:15:07 UTC
Last modified on: 12/27/2024 18:15:38 UTC