CVE-2025-63657 is a vulnerability identified in the Monkey HTTP server, an open-source web server known for its lightweight and efficient design. The flaw exists in the mk_mimetype_find function within the mk_server/mk_mimetype.c source file, where an out-of-bounds read occurs due to improper bounds checking. This vulnerability is classified under CWE-125 (Out-of-bounds Read). An attacker can exploit this by sending a specially crafted HTTP request that triggers the server to read memory outside the intended buffer boundaries. This results in a Denial of Service (DoS) condition, causing the server to crash or become unresponsive, thereby impacting availability. The vulnerability requires no authentication or user interaction and can be exploited remotely over the network, as indicated by the CVSS vector (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H). Although no known exploits are currently reported in the wild and no patches have been published, the high CVSS score of 7.5 reflects the significant risk posed by this flaw. The lack of impact on confidentiality and integrity confines the threat primarily to service disruption. Organizations running Monkey HTTP server should be aware of this vulnerability and prepare to implement mitigations once patches become available.

For European organizations, the primary impact of CVE-2025-63657 is the potential disruption of web services hosted on Monkey HTTP server instances. This can lead to downtime, affecting business continuity, customer access, and potentially causing financial losses. Critical infrastructure or services relying on Monkey HTTP server may experience outages, which could have cascading effects on dependent systems. Since the vulnerability allows remote exploitation without authentication, attackers can launch DoS attacks from anywhere, increasing the risk of large-scale service interruptions. Although no data breach or integrity compromise is involved, the availability impact alone can damage organizational reputation and trust. The absence of known exploits currently provides a window for proactive defense, but the ease of exploitation demands urgent attention. European sectors such as government, finance, and telecommunications that utilize Monkey HTTP server are particularly vulnerable to operational disruptions.

1. Immediately implement network-level protections such as rate limiting and IP filtering to block suspicious or malformed HTTP requests targeting the server. 2. Deploy Web Application Firewalls (WAFs) configured to detect and block anomalous HTTP requests that may exploit out-of-bounds reads. 3. Monitor server logs closely for unusual request patterns or crashes indicative of exploitation attempts. 4. Segregate Monkey HTTP server instances in isolated network segments to limit impact scope in case of successful exploitation. 5. Prepare for rapid patch deployment by tracking Monkey HTTP server updates and applying security patches as soon as they are released. 6. Consider temporary mitigation by disabling or restricting the vulnerable mk_mimetype_find functionality if feasible, or replacing Monkey HTTP server with alternative web servers until a patch is available. 7. Conduct regular vulnerability assessments and penetration testing focused on HTTP request handling to identify similar weaknesses. 8. Educate IT and security teams about this vulnerability to ensure swift detection and response.