CVE-2025-63657
📋 TL;DR
An out-of-bounds read vulnerability in Monkey web server's mk_mimetype_find function allows attackers to cause denial of service by sending specially crafted HTTP requests. This affects Monkey web server deployments using vulnerable versions. Attackers can crash the server without authentication.
💻 Affected Systems
- Monkey web server
📦 What is this software?
Monkey by Monkey Project
⚠️ Risk & Real-World Impact
Worst Case
Complete server crash leading to sustained denial of service, potentially requiring manual restart and causing extended downtime.
Likely Case
Server process crashes when receiving malicious requests, causing temporary service disruption until automatic or manual restart.
If Mitigated
With proper network segmentation and request filtering, impact is limited to isolated service restarts with minimal business disruption.
🎯 Exploit Status
Exploitation requires sending crafted HTTP requests, which is straightforward for attackers with basic networking knowledge.
🛠️ 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 server to version after commit f37e984. 2. Stop the Monkey server service. 3. Install updated version. 4. Restart the Monkey server service.
🔧 Temporary Workarounds
Request Filtering
allImplement web application firewall or reverse proxy to filter suspicious HTTP requests
Network Segmentation
linuxRestrict access to Monkey server to trusted networks only
iptables -A INPUT -p tcp --dport 80 -s trusted_network -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s trusted_network -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP
🧯 If You Can't Patch
- Implement rate limiting to prevent mass exploitation attempts
- Deploy behind reverse proxy with request validation and filtering
🔍 How to Verify
Check if Vulnerable:
Check Monkey server version or commit hash against vulnerable range (up to commit f37e984)Check Version:
monkey --version or check commit hash in source/buildVerify Fix Applied:
Verify installed version is after commit f37e984 and test with sample requests📡 Detection & Monitoring
Log Indicators:
- Server crash logs
- Unexpected process termination
- Error messages mentioning mimetype or out-of-bounds
Network Indicators:
- Unusual HTTP requests with crafted headers or paths
- Multiple connection attempts followed by service unavailability
SIEM Query:
source="monkey.log" AND ("crash" OR "segmentation fault" OR "out of bounds")