CVE-2026-54289 — hono
MEDIUMCVE-2026-54289 is a medium-severity (CVSS 4.8) CWE-348 vulnerability in hono. A fix is available for hono — see the affected versions and patch details below.
Hono: Lambda@Edge adapter keeps only the last value of a repeated request header, dropping the rest
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-54289.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-54289 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 394,803 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
On AWS Lambda@Edge, CloudFront delivers a request header that appears more than once as several separate entries. The adapter writes each value with Headers.set instead of Headers.append, so every value overwrites the previous one and only the last reaches the application. Repeated request headers such as X-Forwarded-For, Forwarded, and Via are silently truncated to a single value.
Details
A repeated request header carries an ordered list of values. The adapter iterates the list but overwrites on each step, keeping only the final value. Middleware that depends on the full list — for example IP restriction that walks the X-Forwarded-For chain, or auditing based on Forwarded/Via hops — receives incomplete data. The API Gateway adapter already appends repeated values and is not affected.
This issue arises only on Lambda@Edge deployments, for requests that contain the same header more than once.
Impact
Request middleware sees only the last value of a repeated header instead of the full chain. For applications that base access control on the X-Forwarded-For chain, this can weaken or alter that decision; for auditing, hop history is lost. This affects applications deployed on AWS Lambda@Edge that rely on multi-value request headers.
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-2026-54289 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.
Frequently Asked Questions
Is CVE-2026-54289 in your dependencies?
Find it across npm, including transitive dependencies.