CVE-2025-59139 is a medium-severity (CVSS 5.3) Uncontrolled Resource Consumption vulnerability in hono. A fix is available for hono — see the affected versions and patch details below.
Hono has Body Limit Middleware Bypass
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2025-59139.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
hononpmDescription
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 should upgrade immediately.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | hono | all versions | 4.9.7npm install hono@4.9.7 |
Affected Products
honohonoDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for hono, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update hono to 4.9.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-59139 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
Frequently Asked Questions
Is CVE-2025-59139 in your dependencies?
Find it across npm, including transitive dependencies.