CVE-2025-63650: Monkey HTTP Server DoS Vulnerability

CVE-2025-63650 Overview

CVE-2025-63650 is an out-of-bounds read vulnerability discovered in the mk_ptr_to_buf function within the mk_core component (mk_memory.c) of the Monkey HTTP Server. This vulnerability exists in commit f37e984 and allows remote attackers to cause a Denial of Service (DoS) condition by sending specially crafted HTTP requests to the server.

Critical Impact
Remote attackers can crash Monkey HTTP Server instances by exploiting this memory safety issue, potentially disrupting web services and causing service unavailability.

Affected Products

Monkey HTTP Server (commit f37e984 and potentially surrounding versions)
Systems running vulnerable versions of the Monkey web server
Applications built on top of the Monkey HTTP Server framework

Discovery Timeline

2026-01-29 - CVE CVE-2025-63650 published to NVD
2026-01-29 - Last updated in NVD database

Technical Details for CVE-2025-63650

Vulnerability Analysis

This vulnerability is classified as an Out-of-Bounds Read, a memory corruption issue that occurs when a program reads data outside the boundaries of allocated memory. In the context of Monkey HTTP Server, the vulnerable mk_ptr_to_buf function in mk_memory.c fails to properly validate memory bounds when processing HTTP request data.

When exploited, the out-of-bounds read can cause the server process to access memory regions it should not, leading to unpredictable behavior. In this case, the primary impact is a Denial of Service condition where the server crashes or becomes unresponsive after processing a maliciously crafted HTTP request.

The vulnerability is triggered through network-accessible HTTP requests, making it exploitable without requiring authentication or local access to the target system.

Root Cause

The root cause of CVE-2025-63650 lies in insufficient boundary checking within the mk_ptr_to_buf function in the mk_core memory handling module. The function appears to process pointer-to-buffer operations without adequately verifying that the read operations remain within the bounds of the allocated memory region.

When handling certain HTTP request patterns, the function may attempt to read beyond the allocated buffer, accessing adjacent memory regions. This improper memory access results in undefined behavior that manifests as a crash or service disruption.

Attack Vector

The attack vector for this vulnerability is network-based. An attacker can exploit this issue by:

Crafting a malicious HTTP request with specific parameters or headers designed to trigger the vulnerable code path
Sending the crafted request to a Monkey HTTP Server instance
The server processes the request and the mk_ptr_to_buf function performs an out-of-bounds read
The memory access violation causes the server process to crash, resulting in denial of service

The vulnerability mechanism involves improper memory boundary validation in the mk_ptr_to_buf function. When processing HTTP requests, the function fails to verify that buffer read operations stay within allocated bounds. Attackers can craft HTTP requests that cause the function to read beyond buffer limits, triggering a crash. For detailed technical analysis, see the GitHub Security Advisory and the GitHub Issue Discussion.

Detection Methods for CVE-2025-63650

Indicators of Compromise

Unexpected Monkey HTTP Server process crashes or restarts
Anomalous HTTP requests with unusual header lengths or malformed parameters in server logs
Memory-related error messages in system logs associated with the Monkey server process
Service availability monitoring alerts indicating repeated server failures

Detection Strategies

Implement network intrusion detection rules to identify malformed HTTP requests targeting Monkey servers
Monitor server process stability and set up alerts for unexpected crashes or restarts
Deploy memory protection mechanisms such as Address Space Layout Randomization (ASLR) and stack canaries
Use web application firewalls (WAF) to filter potentially malicious HTTP requests

Monitoring Recommendations

Enable detailed HTTP request logging on Monkey server instances to capture suspicious request patterns
Configure process monitoring to track the Monkey server process health and automatically restart on failure
Set up network traffic analysis to detect unusual request volumes or patterns targeting the web server
Implement centralized logging to correlate crash events with incoming network requests

How to Mitigate CVE-2025-63650

Immediate Actions Required

Identify all systems running Monkey HTTP Server, particularly those using commit f37e984 or nearby versions
Review access controls and consider restricting network access to vulnerable server instances
Implement rate limiting and request filtering at the network perimeter
Monitor server instances for signs of exploitation attempts or crashes

Patch Information

Organizations should monitor the official Monkey HTTP Server repository for security patches addressing this vulnerability. Check the GitHub Issue Discussion for updates on fix availability and the GitHub Security Advisory for detailed remediation guidance.

Until an official patch is available, organizations should implement the recommended workarounds and consider upgrading to newer versions that may include the fix.

Workarounds

Deploy a reverse proxy or web application firewall in front of Monkey server instances to filter malicious requests
Implement network segmentation to limit exposure of vulnerable server instances
Consider running the server in a sandboxed environment or container to limit crash impact
Enable automatic process restart mechanisms to minimize service downtime from crashes

bash

# Example: Rate limiting with iptables to reduce DoS impact
# Limit incoming connections to the Monkey server port
iptables -A INPUT -p tcp --dport 2001 -m connlimit --connlimit-above 50 -j DROP
iptables -A INPUT -p tcp --dport 2001 -m limit --limit 25/minute --limit-burst 100 -j ACCEPT