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

Severity: high (CVSS 8.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-03-05 · updated 2026-06-17
Weakness: CWE-1336

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.

Affected products

Debian Linux: 11.0
pallets jinja: before 3.1.6 — fixed in 3.1.6
Pypi Jinja2: before 3.1.6; 2.0, 2.0rc1, 2.1, 2.1.1, 2.10, 2.10.1 (+45) — fixed in 3.1.6

How to fix

Upgrade to a fixed version: pallets jinja 3.1.6; Pypi Jinja2 3.1.6. Check the vendor advisory for mitigations.

References

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