CVE-2025-63652: 
Fluent Bit vulnerability analysis and mitigation

CVE-2025-63652 is a use-after-free (UAF) vulnerability in the mk_http_request_end function located in mk_server/mk_http.c of the Monkey HTTP Server. It allows unauthenticated remote attackers to cause a Denial of Service (DoS) by sending a specially crafted HTTP request. The vulnerability affects Monkey HTTP Server through commit f37e984 (versions up to and including 1.8.5). CVE IDs were requested and assigned in October 2025, with public disclosure in January 2026. It carries a CVSS v3.1 base score of 7.5 (High) (Red Hat CVE, Archer Sec Advisory).

The vulnerability is classified as CWE-416 (Use After Free). It occurs in the mk_http_request_end function within mk_server/mk_http.c, where memory that has already been freed is subsequently accessed during HTTP request cleanup, leading to undefined behavior and potential process crash. An unauthenticated attacker can trigger this condition remotely by sending a crafted HTTP request with no special privileges or user interaction required. This vulnerability is part of a broader set of nine security issues discovered in Monkey commit f37e984, reported by researcher archersec in October 2025 (Archer Sec Advisory, GitHub Issue).

Successful exploitation results in a Denial of Service condition, crashing the Monkey HTTP Server and making it unavailable to legitimate users. The vulnerability has no confidentiality or integrity impact — it is limited strictly to availability. Because the server process crashes, any services or applications relying on the Monkey HTTP Server would be disrupted until manually restarted (Red Hat CVE, Archer Sec Advisory).

Proof-of-concept exploit code is publicly available via the archersec security advisory and the associated GitHub issue, which includes a PoC zip archive (monkey-poc.zip) (GitHub Issue, Archer Sec Advisory). There is no evidence of active in-the-wild exploitation at this time, and the vulnerability has not been added to the CISA Known Exploited Vulnerabilities (KEV) catalog. The EPSS score is approximately 0.0051 (low probability of exploitation in the near term). No threat actor attribution has been reported.

1. Reconnaissance: Identify internet-facing or network-accessible Monkey HTTP Server instances running commit f37e984 or versions up to 1.8.5 using network scanning tools such as Shodan, Censys, or Nmap.
2. Obtain PoC: Download or review the publicly available proof-of-concept from the archersec security advisory repository (monkey-poc.zip) (Archer Sec Advisory).
3. Craft malicious HTTP request: Construct a specially crafted HTTP request designed to trigger the use-after-free condition in the mk_http_request_end function during request cleanup in mk_server/mk_http.c.
4. Send request to target: Transmit the crafted HTTP request to the target Monkey HTTP Server. No authentication or special privileges are required.
5. Achieve DoS: The server accesses freed memory during request teardown, causing a crash and rendering the HTTP server unavailable to legitimate users (GitHub Issue).

• Network: Unusual or malformed HTTP requests targeting the Monkey HTTP Server, particularly requests that trigger abnormal connection teardown sequences; repeated connection attempts from a single source IP.
• Logs: Monkey HTTP Server access or error logs showing abrupt process termination or segmentation fault messages correlated with specific client requests; crash dump files generated by the server process.
• Process: Unexpected termination or restart of the Monkey HTTP Server process (monkey or mk_server); core dump files (e.g., core.*) appearing in the server's working directory.
• File System: Presence of monkey-poc.zip or related PoC files on attacker-controlled systems that have interacted with the server (Archer Sec Advisory).

As of the time of disclosure, no official patch has been released for Monkey HTTP Server — the vulnerability remains unfixed in all versions through commit f37e984 (up to and including 1.8.5) (Archer Sec Advisory). Recommended interim mitigations include: restricting network access to the Monkey HTTP Server using firewall rules or network-level controls; monitoring for anomalous HTTP request patterns; and considering disabling the service if it is not critical to operations. Organizations should monitor the official Monkey project repository and security advisories for the release of a patched version and upgrade immediately upon availability (Red Hat CVE).

Red Hat has acknowledged the vulnerability and published a CVE tracking page (Red Hat CVE). The vulnerability was reported as part of a coordinated disclosure of nine issues in Monkey HTTP Server by researcher archersec, who published a detailed advisory on GitHub (Archer Sec Advisory). No significant broader media coverage or notable community commentary beyond the initial disclosure has been identified.