CVE-2025-63658 Overview
A stack overflow vulnerability has been identified in the Monkey HTTP Server, specifically within the mk_http_index_lookup function located in mk_server/mk_http.c. This vulnerability exists in Monkey 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 the Monkey HTTP Server by sending malicious HTTP requests, causing service unavailability for legitimate users.
Affected Products
- Monkey HTTP Server (commit f37e984)
Discovery Timeline
- 2026-01-29 - CVE-2025-63658 published to NVD
- 2026-01-29 - Last updated in NVD database
Technical Details for CVE-2025-63658
Vulnerability Analysis
This vulnerability is a stack overflow condition that occurs during HTTP request processing in the Monkey HTTP Server. The mk_http_index_lookup function fails to properly validate input boundaries when processing incoming HTTP requests, allowing an attacker to overflow the stack buffer. When exploited, this causes the server process to crash, resulting in denial of service.
The vulnerability is particularly concerning for production deployments of Monkey HTTP Server as it can be triggered remotely without authentication. Any system exposed to untrusted network traffic running the affected version is at risk of service disruption.
Root Cause
The root cause of this vulnerability lies in insufficient bounds checking within the mk_http_index_lookup function in mk_server/mk_http.c. When processing HTTP requests with specially crafted input, the function writes data beyond the allocated stack buffer boundaries, leading to stack corruption and process termination.
Attack Vector
The attack vector involves sending a maliciously crafted HTTP request to the Monkey HTTP Server. An attacker does not require any authentication or special privileges to exploit this vulnerability. The attack can be executed remotely over the network by any client capable of establishing an HTTP connection to the vulnerable server.
The exploitation involves crafting an HTTP request with specific parameters that trigger the vulnerable code path in mk_http_index_lookup, causing the stack buffer to overflow and crash the server process.
Detection Methods for CVE-2025-63658
Indicators of Compromise
- Unexpected Monkey HTTP Server process crashes or restarts
- Segmentation fault errors in server logs related to stack corruption
- Unusual HTTP request patterns with abnormally long or malformed headers
- Repeated service availability interruptions without apparent cause
Detection Strategies
- Monitor Monkey HTTP Server process stability and implement automatic restart detection
- Analyze HTTP access logs for requests with abnormally large headers or unusual formatting
- Deploy intrusion detection systems (IDS) with signatures for stack overflow exploitation attempts
- Implement application-level monitoring to detect crash patterns indicative of DoS attacks
Monitoring Recommendations
- Configure alerting for Monkey HTTP Server process termination events
- Monitor system logs for segmentation fault signals associated with the server process
- Track HTTP request sizes and flag anomalously large requests for review
- Implement real-time monitoring of server availability and response times
How to Mitigate CVE-2025-63658
Immediate Actions Required
- Review and upgrade Monkey HTTP Server to a patched version if available
- Implement network-level filtering to restrict access to trusted clients where possible
- Deploy a Web Application Firewall (WAF) to filter malicious HTTP requests
- Consider temporarily disabling the affected service if it cannot be immediately patched
Patch Information
Affected organizations should monitor the official Monkey HTTP Server repository for security patches addressing this vulnerability. For detailed information about the vulnerability and remediation steps, refer to the GitHub Security Advisory and the GitHub Issue Tracker.
Workarounds
- Place the Monkey HTTP Server behind a reverse proxy that performs request validation and sanitization
- Implement request size limits at the network or load balancer level to filter oversized requests
- Restrict network access to the server using firewall rules to limit exposure to trusted networks only
- Enable process monitoring and automatic restart to minimize service downtime in case of exploitation
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
