CVE-2025-27516
📋 TL;DR
CVE-2025-27516 is a sandbox escape vulnerability in Jinja templating engine that allows attackers who control template content to execute arbitrary Python code. This affects applications that process untrusted templates, potentially leading to remote code execution. Only users who execute untrusted Jinja templates are vulnerable.
💻 Affected Systems
- Jinja
- Applications using Jinja templating engine
📦 What is this software?
Jinja by Palletsprojects
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with the privileges of the application, potentially leading to complete system compromise, data theft, or lateral movement.
Likely Case
Template injection leading to arbitrary code execution within the application context, allowing data exfiltration or further exploitation.
If Mitigated
No impact if applications only process trusted templates or have proper input validation and sandboxing controls.
🎯 Exploit Status
Exploitation requires attacker to control template content. The vulnerability bypasses sandbox restrictions using the |attr filter to access string.format method.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Jinja 3.1.6
Vendor Advisory: https://github.com/pallets/jinja/security/advisories/GHSA-cpwx-vrp4-4pq7
Restart Required: No
Instructions:
1. Update Jinja to version 3.1.6 or later using pip: pip install --upgrade Jinja2>=3.1.6
2. Verify the update was successful
3. No application restart required for Python package updates
🔧 Temporary Workarounds
Disable untrusted template processing
allModify applications to only process trusted templates or disable template processing from untrusted sources
Implement strict input validation
allAdd validation to reject templates containing suspicious patterns like |attr filter usage with format methods
🧯 If You Can't Patch
- Implement network segmentation to isolate vulnerable applications
- Deploy application firewalls with template injection detection rules
🔍 How to Verify
Check if Vulnerable:
Check Jinja version: python -c "import jinja2; print(jinja2.__version__)" and verify if below 3.1.6Check Version:
python -c "import jinja2; print(jinja2.__version__)"Verify Fix Applied:
After update, verify version is 3.1.6 or higher using same command📡 Detection & Monitoring
Log Indicators:
- Unusual template processing errors
- Unexpected Python execution in application logs
- Template content containing |attr filter with format
Network Indicators:
- Unusual outbound connections from application servers
- Unexpected data exfiltration patterns
SIEM Query:
template_content:"|attr" AND template_content:"format" OR process_execution:python FROM application_servers