CVE-2026-22903
📋 TL;DR
An unauthenticated remote attacker can crash or potentially execute arbitrary code on lighttpd web servers by sending a specially crafted HTTP request with an overly long SESSIONID cookie. This stack buffer overflow vulnerability affects modified lighttpd installations that lack stack protection mechanisms. Any internet-facing lighttpd server with the vulnerable modification is at risk.
💻 Affected Systems
- Modified lighttpd
⚠️ 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
Remote code execution with full system compromise, allowing attacker to install malware, steal data, or pivot to other systems.
Likely Case
Denial of service through server crashes, potentially leading to service disruption and availability issues.
If Mitigated
Limited to denial of service if stack protections are enabled or the server is properly isolated.
🎯 Exploit Status
Exploitation requires sending a simple HTTP request with a long cookie value. No authentication needed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Not specified
Vendor Advisory: https://certvde.com/de/advisories/VDE-2026-004
Restart Required: Yes
Instructions:
1. Contact the vendor/modifier of your lighttpd installation for patches. 2. If no patch available, apply workarounds. 3. Restart lighttpd after any changes.
🔧 Temporary Workarounds
Cookie Length Limiting
allConfigure lighttpd to reject HTTP requests with SESSIONID cookies exceeding a safe length (e.g., 4096 bytes)
# Add to lighttpd.conf:
server.max-request-field-size = 8192
# Or implement custom mod_magnet script to check cookie length
Network Filtering
allUse WAF or reverse proxy to filter requests with overly long cookies before they reach lighttpd
# Example nginx config:
location / {
proxy_set_header Cookie $http_cookie;
# Add length checking logic
proxy_pass http://lighttpd_backend;
}
🧯 If You Can't Patch
- Isolate vulnerable servers in network segments with strict firewall rules limiting access
- Implement intrusion detection systems to monitor for exploitation attempts and long cookie values
🔍 How to Verify
Check if Vulnerable:
Test by sending HTTP request with SESSIONID cookie exceeding typical length (e.g., 10000+ characters) and monitor for crash or abnormal behaviorCheck Version:
lighttpd -vVerify Fix Applied:
After applying workarounds, retest with long cookie requests - server should reject or handle without crashing📡 Detection & Monitoring
Log Indicators:
- HTTP requests with unusually long cookie values
- lighttpd crash logs or core dumps
- Repeated connection failures
Network Indicators:
- HTTP traffic with SESSIONID cookie length > 4096 bytes
- Multiple rapid requests to trigger overflow
SIEM Query:
source="lighttpd" AND (cookie_length>4096 OR message="*crash*" OR message="*segfault*")