CVE-2025-63656
📋 TL;DR
An out-of-bounds read vulnerability in Monkey web server's HTTP parser allows attackers to cause denial of service by sending crafted HTTP requests. This affects systems running vulnerable versions of Monkey web server, potentially disrupting web services.
💻 Affected Systems
- Monkey web server
⚠️ Risk & Real-World Impact
Worst Case
Complete service disruption through server crash, potentially leading to extended downtime and service unavailability.
Likely Case
Server process crashes requiring restart, causing temporary service interruption until recovery.
If Mitigated
Service interruption limited to affected worker processes if load balancing and process isolation are implemented.
🎯 Exploit Status
Exploitation requires network access to the vulnerable service but no authentication.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Versions after commit f37e984
Vendor Advisory: https://github.com/archersec/security-advisories/blob/master/monkey/monkey-advisory-2025.md
Restart Required: Yes
Instructions:
1. Update Monkey to a version after commit f37e984. 2. Rebuild from source if using source distribution. 3. Restart the Monkey service.
🔧 Temporary Workarounds
Network filtering
allImplement WAF or network filtering to block malformed HTTP requests.
Process monitoring and auto-restart
linuxConfigure process monitoring to automatically restart Monkey if it crashes.
systemctl edit monkey
Add Restart=always to service file
🧯 If You Can't Patch
- Implement rate limiting to reduce impact of repeated attacks
- Deploy behind reverse proxy with request validation
🔍 How to Verify
Check if Vulnerable:
Check Monkey version or commit hash against vulnerable range (up to f37e984).Check Version:
monkey --version or check build commit hashVerify Fix Applied:
Verify running version is newer than commit f37e984 and test with known exploit patterns.📡 Detection & Monitoring
Log Indicators:
- Unexpected server crashes
- Error logs mentioning header parsing failures
- Segmentation fault in Monkey process
Network Indicators:
- Malformed HTTP requests with unusual header patterns
- Rapid connection attempts to trigger DoS
SIEM Query:
source="monkey.log" AND ("segmentation fault" OR "crash" OR "out of bounds")