CVE-2025-63653
📋 TL;DR
An out-of-bounds read vulnerability in Monkey web server's mk_vhost_fdt_close function allows attackers to cause denial of service by sending crafted HTTP requests. This affects Monkey web server deployments exposed to untrusted network traffic. The vulnerability can crash the server process, disrupting web services.
💻 Affected Systems
- Monkey web server
⚠️ Risk & Real-World Impact
Worst Case
Complete service disruption with server crashes requiring manual restart, potentially leading to extended downtime for web applications.
Likely Case
Intermittent service disruption with server crashes affecting availability until automatic or manual recovery.
If Mitigated
Limited impact with proper network segmentation and monitoring allowing quick detection and recovery.
🎯 Exploit Status
Crafting HTTP requests to trigger the out-of-bounds read requires minimal technical skill. No authentication is required to exploit.
🛠️ 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. Stop the Monkey service. 3. Replace the binary with the patched version. 4. Restart the Monkey service.
🔧 Temporary Workarounds
Network filtering
linuxImplement network filtering to block suspicious HTTP requests that might trigger the vulnerability.
iptables -A INPUT -p tcp --dport 80 -m string --string "malicious-pattern" --algo bm -j DROP
Load balancer protection
allConfigure load balancers or WAF to filter abnormal HTTP requests before they reach Monkey servers.
🧯 If You Can't Patch
- Implement strict network segmentation to limit access to Monkey servers only from trusted sources.
- Deploy monitoring and automated restart mechanisms to detect and recover from crashes quickly.
🔍 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 the source commit hash if built from source.Verify Fix Applied:
Verify the Monkey version is after commit f37e984 and test with normal HTTP traffic to ensure stability.📡 Detection & Monitoring
Log Indicators:
- Server crash logs
- Segmentation fault errors in system logs
- Unexpected process termination
Network Indicators:
- Abnormal HTTP request patterns
- Multiple connection attempts with malformed headers
SIEM Query:
source="monkey.log" AND ("segmentation fault" OR "crash" OR "abort")