CVE-2025-27516: 
Python vulnerability analysis and mitigation

CVE-2025-27516 is a security vulnerability discovered in Jinja, an extensible templating engine, affecting versions prior to 3.1.6. The vulnerability was disclosed on March 5, 2025, and impacts applications that execute untrusted templates (NVD, GitHub Advisory).

The vulnerability stems from an oversight in how the Jinja sandboxed environment interacts with the |attr filter. While Jinja's sandbox catches calls to str.format and ensures they don't escape the sandbox, attackers can use the |attr filter to get a reference to a string's plain format method, effectively bypassing the sandbox protection. The vulnerability has been assigned a CVSS v4.0 base score of 5.4 (Medium) with the vector string CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N (GitHub Advisory).

If successfully exploited, this vulnerability allows an attacker who controls the content of a template to execute arbitrary Python code. The impact is particularly severe for applications that execute untrusted templates, potentially leading to complete system compromise with high impacts on confidentiality, integrity, and availability of the vulnerable system (Red Hat).

The vulnerability has been fixed in Jinja version 3.1.6. After the fix, the |attr filter no longer bypasses the environment's attribute lookup. Users are strongly advised to upgrade to this version or later. The fix ensures that the |attr filter properly respects the environment's attribute lookup, allowing the sandbox to apply its security checks (GitHub Advisory).