CVE-2025-63658
📋 TL;DR
A stack overflow vulnerability in Monkey web server's mk_http_index_lookup function allows attackers to cause denial of service by sending specially crafted HTTP requests. This affects Monkey web server deployments using vulnerable versions. The vulnerability can crash the server process, disrupting web services.
💻 Affected Systems
- Monkey web server
📦 What is this software?
Monkey by Monkey Project
⚠️ Risk & Real-World Impact
Worst Case
Complete service disruption with server crash, potentially requiring manual restart and causing extended downtime.
Likely Case
Service interruption and server crashes requiring restart, leading to temporary unavailability of hosted websites or applications.
If Mitigated
Limited impact with quick recovery if monitoring and automated restart mechanisms are in place.
🎯 Exploit Status
Exploitation requires sending crafted HTTP requests but no authentication. The vulnerability is in a core HTTP handling function.
🛠️ 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. 4. Verify the fix is applied.
🔧 Temporary Workarounds
Rate limiting and request filtering
linuxImplement network-level controls to limit request rates and filter suspicious HTTP requests
iptables -A INPUT -p tcp --dport 80 -m limit --limit 100/minute -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -m limit --limit 100/minute -j ACCEPT
Reverse proxy with request validation
allPlace Monkey behind a reverse proxy that validates and sanitizes HTTP requests
# Configure nginx/apache as reverse proxy with request size limits
🧯 If You Can't Patch
- Implement network segmentation to isolate Monkey servers from untrusted networks
- Deploy web application firewall (WAF) with DoS protection rules
🔍 How to Verify
Check if Vulnerable:
Check Monkey version or commit hash. If using commit f37e984 or earlier, the system is vulnerable.Check Version:
monkey --version or check commit hash in source directoryVerify Fix Applied:
Verify Monkey version is after commit f37e984 and test with normal HTTP requests to ensure service stability.📡 Detection & Monitoring
Log Indicators:
- Server crash logs
- Segmentation fault errors
- Abnormal termination of monkey process
Network Indicators:
- Unusually large HTTP requests
- Multiple connection attempts with malformed requests
SIEM Query:
process.name="monkey" AND (event.action="crash" OR event.outcome="failure")