CVE-2025-27516: Jinja sandbox breakout through attr filter selecting format method

Vulnerability summary

CVE-2025-27516 is a high (CVSS 8.8) vulnerability in debian debian_linux. EPSS estimates a 0.51% chance of exploitation in the next 30 days, higher than 43.3% of scored vulnerabilities.

Timeline

1. 05-03-2025
   PublishedVulnerability first disclosed.
2. 26-02-2026
   Last modifiedVulnerability information updated.

Description

Jinja is an extensible templating engine. Prior to 3.1.6, an oversight in how the Jinja sandboxed environment interacts with the |attr filter allows an attacker that controls the content of a template to execute arbitrary Python code. To exploit the vulnerability, an attacker needs to control the content of a template. Whether that is the case depends on the type of application using Jinja. This vulnerability impacts users of applications which execute untrusted templates. Jinja's sandbox does catch calls to str.format and ensures they don't escape the sandbox. However, it's possible to use the |attr filter to get a reference to a string's plain format method, bypassing the sandbox. After the fix, the |attr filter no longer bypasses the environment's attribute lookup. This vulnerability is fixed in 3.1.6.

• CWE-1336Improper Neutralization of Special Elements Used in a Template EngineThe product uses a template engine to insert or process externally-influenced input, but it does not neutralize or incorrectly neutralizes special elements or syntax that can be interpreted as template expressions or other code directives when processed by the engine.