CVE-2024-6827
📋 TL;DR
CVE-2024-6827 is a HTTP request smuggling vulnerability in Gunicorn 21.2.0 where improper Transfer-Encoding header validation allows attackers to bypass security controls. This affects any system using the vulnerable Gunicorn version as a web server or reverse proxy, potentially enabling cache poisoning, session hijacking, and data exposure.
💻 Affected Systems
- Gunicorn
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Attackers could poison caches to serve malicious content to all users, hijack user sessions, perform SSRF attacks against internal systems, and bypass authentication mechanisms entirely.
Likely Case
Cache poisoning leading to stored XSS attacks, session manipulation for targeted users, and information leakage through request smuggling.
If Mitigated
With proper WAF rules and request validation, impact is limited to potential DoS through malformed requests.
🎯 Exploit Status
Exploitation requires crafting specific HTTP requests with conflicting Transfer-Encoding and Content-Length headers. No authentication is needed to trigger the vulnerability.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 21.2.1
Vendor Advisory: https://github.com/benoitc/gunicorn/security/advisories/GHSA-8fjx-3jrw-ggfr
Restart Required: Yes
Instructions:
1. Update Gunicorn using pip: 'pip install --upgrade gunicorn==21.2.1' 2. Restart all Gunicorn processes 3. Verify the version with 'gunicorn --version'
🔧 Temporary Workarounds
WAF Rule for TE.CL Protection
allConfigure web application firewall to block requests with conflicting Transfer-Encoding and Content-Length headers
# Example nginx config: location / { if ($http_transfer_encoding ~* "chunked") { return 400; } }
Reverse Proxy Validation
allConfigure upstream reverse proxies to normalize and validate HTTP headers before passing to Gunicorn
# Example Apache mod_security rule: SecRule REQUEST_HEADERS:Transfer-Encoding "@rx chunked" "id:1001,phase:1,deny"
🧯 If You Can't Patch
- Deploy a WAF with HTTP request smuggling protection rules enabled
- Place Gunicorn behind a reverse proxy that validates and normalizes HTTP headers
🔍 How to Verify
Check if Vulnerable:
Check Gunicorn version with 'gunicorn --version' or 'pip show gunicorn'. If version is exactly 21.2.0, the system is vulnerable.Check Version:
gunicorn --versionVerify Fix Applied:
After patching, verify version is 21.2.1 or higher with 'gunicorn --version'. Test with crafted TE.CL requests to confirm they are rejected.📡 Detection & Monitoring
Log Indicators:
- Multiple requests with same connection ID
- Requests with malformed Transfer-Encoding headers
- Unexpected 400/413 errors from Gunicorn
Network Indicators:
- HTTP requests containing both Transfer-Encoding: chunked and Content-Length headers
- Abnormal request patterns with conflicting headers
SIEM Query:
source="gunicorn-access.log" AND ("Transfer-Encoding" AND "Content-Length") OR status=400