CVE-2026-54288 — hono
MEDIUMCVE-2026-54288 is a medium-severity (CVSS 6.5) CWE-345 vulnerability in hono. A fix is available for hono — see the affected versions and patch details below.
Hono: Body Limit Middleware can be bypassed on AWS Lambda by understating `Content-Length`
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-2026-54288.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-54288 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 395,308 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
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
Summary
The Body Limit Middleware trusts the request's Content-Length header to decide whether a body is within the limit. On AWS Lambda (API Gateway v1/v2, ALB, VPC Lattice, and Lambda@Edge) the body is delivered fully buffered and the adapter builds the request with the client-declared Content-Length, which need not match the actual payload. A client can declare a tiny Content-Length while sending a much larger body, slipping past the limit.
Details
When Content-Length is present and Transfer-Encoding is absent, the middleware compares the declared value against the limit and passes the request through if it is small enough. On standards-based runtimes the transport enforces that Content-Length matches the body, so this is safe. The Lambda adapters instead reconstruct the request from a buffered payload and copy the client's Content-Length verbatim, so the declared length and the real body size are decoupled.
This issue affects applications deployed on AWS Lambda that rely on the Body Limit Middleware to cap request body size.
Impact
The declared body-size limit can be bypassed: a handler reads a payload larger than the configured maximum. Processing the oversized payload (large JSON, multipart, etc.) consumes additional CPU and memory per request. The payload remains bounded by the platform's request size limits, and Lambda isolates invocations, so the impact is increased per-request resource usage rather than full denial of service. This affects applications deployed on AWS Lambda that use the Body Limit Middleware.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | hono | all versions | 4.12.25npm install hono@4.12.25 |
Detection & 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 4.12.25 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-54288 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-2026-54288 in your dependencies?
Find it across npm, including transitive dependencies.