Is there a public exploit for CVE-2025-59139?

Yes. Proof-of-concept code for CVE-2025-59139 has been published publicly.

Is there a proof of concept for CVE-2025-59139?

Yes — 1 proof-of-concept entry is linked on this page, from public repositories and community submissions. They are listed for authorised testing only.

How severe is CVE-2025-59139?

CVE-2025-59139 scores CVSS 5.3 (v3.1), rated medium. EPSS puts the chance of exploitation in the next 30 days at 0.45%.

What does CVE-2025-59139 affect?

CVE-2025-59139 affects honojs hono.

5.3 Medium

Hono is a Web application framework that provides support for any JavaScript runtime.

CVE-2025-59139

Hono is a Web application framework that provides support for any JavaScript runtime. In versions prior to 4.9.7, a flaw in the bodyLimit middleware could allow bypassing the configured request body size limit when conflicting HTTP headers were present. The middleware previously prioritized the Content-Length header even when a Transfer-Encoding: chunked header was also included. According to the HTTP specification, Content-Length must be ignored in such cases. This discrepancy could allow oversized request bodies to bypass the configured limit. Most standards-compliant runtimes and reverse proxies may reject such malformed requests with 400 Bad Request, so the practical impact depends on the runtime and deployment environment. If body size limits are used as a safeguard against large or malicious requests, this flaw could allow attackers to send oversized request bodies. The primary risk is denial of service (DoS) due to excessive memory or CPU consumption when handling very large requests. The implementation has been updated to align with the HTTP specification, ensuring that Transfer-Encoding takes precedence over Content-Length. The issue is fixed in Hono v4.9.7, and all users…

Proof-of-concept code is published

Public PoC

Public PoCRoninForge/roninforge-hono

Signals come from Exploit-DB, Metasploit, Nuclei and published proof-of-concept repositories. Their absence means nothing was found, not that nothing exists.

Assessment

CVSS: 5.3 (v3.1)
Severity: Medium
EPSS: 0.45% chance of exploitation in the next 30 days
Known exploited: Not listed in CISA KEV
Exploit availability: Public PoC
Published: 12 September 2025
Last updated: 17 June 2026
Affected: honojs · hono
Weakness: CWE-400, CWE-770
Assigner: security-advisories@github.com

CVSS vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

At the source

References

Community proofs of concept

No community proof of concept yet. If you have one for a published vulnerability and the right to share it, add it below — it will appear here once reviewed.

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