CVE-2019-8341
📋 TL;DR
CVE-2019-8341 is a Server-Side Template Injection vulnerability in Jinja2 2.10 that allows attackers to execute arbitrary code by injecting malicious template commands. This affects applications that use Jinja2's from_string function with untrusted template sources. The vulnerability is disputed by maintainers who argue proper sandboxing should prevent exploitation.
💻 Affected Systems
- Jinja2
📦 What is this software?
Jinja2 by Pocoo
Leap by Opensuse
Leap by Opensuse
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data theft, and lateral movement within the network.
Likely Case
Information disclosure, limited code execution within application context, or denial of service.
If Mitigated
No impact if proper sandboxing is implemented or untrusted templates are not processed.
🎯 Exploit Status
Exploitation requires access to template injection point. Public proof-of-concept demonstrates code execution via {{INJECTION COMMANDS}}.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Versions after 2.10
Vendor Advisory: https://github.com/pallets/jinja/issues/834
Restart Required: No
Instructions:
1. Upgrade Jinja2 to version 2.10.1 or later. 2. Update requirements.txt or package manager. 3. Test application functionality after upgrade.
🔧 Temporary Workarounds
Implement Jinja2 Sandbox
allUse Jinja2's sandboxed environment for processing untrusted templates
from jinja2.sandbox import SandboxedEnvironment
env = SandboxedEnvironment()
template = env.from_string(template_string)
Input Validation
allValidate and sanitize all template inputs before processing
🧯 If You Can't Patch
- Implement strict input validation for all template sources
- Deploy web application firewall with SSTI detection rules
🔍 How to Verify
Check if Vulnerable:
Check Jinja2 version: pip show Jinja2 | grep Version. If version is exactly 2.10, check if from_string is used with untrusted input.Check Version:
pip show Jinja2 | grep VersionVerify Fix Applied:
Verify Jinja2 version is 2.10.1 or later: pip show Jinja2 | grep Version📡 Detection & Monitoring
Log Indicators:
- Unusual template rendering errors
- Suspicious template syntax in logs
- Multiple failed template parsing attempts
Network Indicators:
- HTTP requests containing {{, }}, or template injection patterns
- Unusual outbound connections from application server
SIEM Query:
search template_rendering_error OR "{{*}}" in web_logs🔗 References
- http://lists.opensuse.org/opensuse-security-announce/2019-05/msg00030.html
- http://lists.opensuse.org/opensuse-security-announce/2019-06/msg00064.html
- https://bugzilla.redhat.com/show_bug.cgi?id=1677653
- https://bugzilla.suse.com/show_bug.cgi?id=1125815
- https://github.com/JameelNabbo/Jinja2-Code-execution
- https://www.exploit-db.com/exploits/46386/
- http://lists.opensuse.org/opensuse-security-announce/2019-05/msg00030.html
- http://lists.opensuse.org/opensuse-security-announce/2019-06/msg00064.html
- https://bugzilla.redhat.com/show_bug.cgi?id=1677653
- https://bugzilla.suse.com/show_bug.cgi?id=1125815
- https://github.com/JameelNabbo/Jinja2-Code-execution
- https://www.exploit-db.com/exploits/46386/
