CVE-2025-63655
📋 TL;DR
This vulnerability allows attackers to crash Monkey web servers by sending specially crafted HTTP requests that trigger a NULL pointer dereference. Any system running vulnerable versions of Monkey web server is affected, potentially causing service disruption.
💻 Affected Systems
- Monkey web server
⚠️ Risk & Real-World Impact
Worst Case
Complete denial of service causing the Monkey web server process to crash, requiring manual restart and potentially disrupting all hosted services.
Likely Case
Service disruption affecting availability of web applications hosted on Monkey server, with automatic or manual restart required to restore service.
If Mitigated
Minimal impact if proper network segmentation, rate limiting, and monitoring are in place to detect and block malicious requests.
🎯 Exploit Status
Exploitation requires sending a crafted HTTP request but no authentication or special privileges. The vulnerability is straightforward to trigger.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check GitHub repository for fixes after commit f37e984
Vendor Advisory: https://github.com/archersec/security-advisories/blob/master/monkey/monkey-advisory-2025.md
Restart Required: Yes
Instructions:
1. Update to latest Monkey version from official repository. 2. Rebuild from source if using custom builds. 3. Restart Monkey service after update.
🔧 Temporary Workarounds
HTTP Request Filtering
allUse reverse proxy or WAF to filter malformed HTTP range requests
# Configure nginx/apache to sanitize Range headers
# Example: proxy_set_header Range "";
Rate Limiting
linuxImplement rate limiting to prevent repeated exploitation attempts
# iptables example: iptables -A INPUT -p tcp --dport 80 -m limit --limit 10/min -j ACCEPT
# iptables -A INPUT -p tcp --dport 80 -j DROP
🧯 If You Can't Patch
- Implement network segmentation to isolate Monkey servers from untrusted networks
- Deploy web application firewall (WAF) with rules to detect and block malformed HTTP range requests
🔍 How to Verify
Check if Vulnerable:
Check if Monkey version includes commit f37e984 or earlier. Review build logs or version strings.Check Version:
monkey --version or check build configuration filesVerify Fix Applied:
Verify updated version no longer contains the vulnerable commit. Test with crafted HTTP range requests.📡 Detection & Monitoring
Log Indicators:
- Monkey process crashes
- Segmentation fault errors in logs
- Unusual HTTP requests with malformed Range headers
Network Indicators:
- HTTP requests with crafted Range headers
- Multiple connection attempts followed by service unavailability
SIEM Query:
source="monkey.log" AND ("segmentation fault" OR "SIGSEGV" OR "null pointer")