CVE-2025-63650 is a security vulnerability identified in the Monkey HTTP server software, specifically within the mk_ptr_to_buf function located in the mk_core module (file mk_memory.c). The flaw is an out-of-bounds read, which occurs when the function attempts to access memory beyond the allocated buffer boundaries. This type of memory access error can lead to undefined behavior, including application crashes. An attacker can exploit this vulnerability by sending a specially crafted HTTP request designed to trigger the out-of-bounds read condition. The result is a Denial of Service (DoS) attack, where the Monkey server becomes unresponsive or crashes, disrupting service availability. The vulnerability was reserved on October 27, 2025, and published on January 29, 2026, but no CVSS score or patches have been released yet. No known exploits have been observed in the wild, indicating it may be a recently discovered issue. The affected versions are not specified, which suggests that users of any Monkey server version should consider themselves potentially vulnerable until confirmed otherwise. The vulnerability does not require authentication or user interaction beyond sending a crafted HTTP request, making it relatively easy to exploit remotely. The lack of a patch or mitigation guidance increases the risk for organizations relying on Monkey HTTP server for web services or embedded applications. This vulnerability primarily impacts the availability of services, as it causes server crashes or hangs, but does not directly affect confidentiality or integrity. Given the nature of the vulnerability, attackers could disrupt web services, leading to operational downtime and potential reputational damage for affected organizations.

For European organizations, the primary impact of CVE-2025-63650 is service disruption due to Denial of Service attacks against Monkey HTTP servers. Organizations using Monkey as a web server or embedded HTTP server in network devices or IoT infrastructure may experience outages, affecting business continuity and customer access to online services. Critical sectors such as telecommunications, government services, and financial institutions that rely on stable web infrastructure could face operational risks. The disruption could also impact supply chains if web-based services are integral to operations. Although the vulnerability does not appear to compromise data confidentiality or integrity directly, the loss of availability can have cascading effects, including loss of trust and potential regulatory scrutiny under European data protection laws if service interruptions affect user access or data processing. The absence of patches means organizations must rely on network-level mitigations and monitoring until a fix is available. The ease of exploitation without authentication increases the threat level, especially for externally facing servers. Organizations with limited visibility into their web server software stack may be unaware of their exposure, increasing risk.

1. Immediately inventory and identify all instances of Monkey HTTP server within the organization’s infrastructure, including embedded devices and network appliances. 2. Restrict external access to Monkey HTTP servers using firewalls or network segmentation to limit exposure to untrusted networks. 3. Implement Web Application Firewalls (WAFs) or intrusion prevention systems (IPS) with custom rules to detect and block malformed or suspicious HTTP requests that could trigger the vulnerability. 4. Monitor server logs and network traffic for unusual HTTP request patterns indicative of exploitation attempts. 5. Engage with Monkey HTTP server developers or community to obtain updates on patches or workarounds and apply them promptly once available. 6. Consider temporary mitigation by disabling or replacing Monkey HTTP server with alternative web servers if feasible. 7. Develop and test incident response plans specifically for DoS scenarios affecting web services to minimize downtime. 8. Educate IT and security teams about this vulnerability and the importance of rapid detection and response. 9. For embedded devices using Monkey, coordinate with vendors for firmware updates or mitigations. 10. Maintain up-to-date backups and redundancy for critical web services to ensure availability during incidents.