CVE-2025-63649 is a security vulnerability identified in the Monkey HTTP server, specifically within the http_parser_transfer_encoding_chunked function located in the mk_server/mk_http_parser.c source file. The flaw is an out-of-bounds read error triggered when processing HTTP POST requests with chunked transfer encoding. An attacker can exploit this by sending a crafted POST request that causes the server to read memory outside the intended buffer bounds. This memory access violation can lead to a Denial of Service (DoS) condition, crashing the server or causing it to become unresponsive. The vulnerability was reserved in late 2025 and published in early 2026, but no CVSS score or patch links are currently available. No known exploits have been reported in the wild, indicating it may not yet be actively targeted. The lack of detailed affected versions suggests the issue may be present in multiple or all recent Monkey server releases. Exploitation requires network access to the HTTP server to send malicious POST requests but does not require authentication or user interaction. The vulnerability impacts the availability of services hosted on the Monkey server by enabling attackers to disrupt normal operations through crafted HTTP traffic. Monkey is a lightweight web server often used in embedded systems and IoT devices, which may have limited security monitoring, increasing the risk of unnoticed exploitation.

For European organizations, the primary impact of CVE-2025-63649 is service disruption due to Denial of Service attacks on servers running the Monkey HTTP server. This can affect web-facing applications, embedded devices, or IoT infrastructure that rely on Monkey for HTTP communication. Disruptions could lead to downtime, loss of availability of critical services, and potential cascading effects if the affected servers are part of larger operational technology or industrial control systems. Organizations in sectors such as telecommunications, manufacturing, smart city infrastructure, and critical national infrastructure that utilize embedded devices with Monkey server could face operational interruptions. The absence of known exploits reduces immediate risk but also means organizations should proactively assess exposure. The vulnerability does not appear to compromise confidentiality or integrity directly but could be leveraged as part of a broader attack chain to degrade service or distract defenders. European entities with limited patch management or visibility into embedded device software stacks may be particularly vulnerable to unnoticed exploitation attempts.

1. Monitor official Monkey HTTP server repositories and security advisories for patches addressing CVE-2025-63649 and apply them promptly once available. 2. Implement network-level filtering to restrict access to Monkey HTTP servers, allowing only trusted IP addresses or internal networks to send POST requests. 3. Deploy Web Application Firewalls (WAFs) or intrusion prevention systems capable of detecting and blocking malformed or suspicious HTTP chunked transfer encoding requests. 4. Conduct thorough inventory and risk assessment of embedded devices and IoT systems running Monkey server to identify exposed instances. 5. Employ rate limiting on HTTP POST requests to reduce the risk of DoS from crafted traffic. 6. Enhance logging and monitoring to detect abnormal HTTP request patterns indicative of exploitation attempts. 7. Where feasible, isolate vulnerable devices from critical network segments to limit impact. 8. Educate operational technology and embedded system teams about this vulnerability to ensure timely response and mitigation.