CVE-2026-54289
MEDIUMHono: Lambda@Edge adapter keeps only the last value of a repeated request header, dropping the rest
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
Weekly download volume for affected packages — a proxy for how broadly this vulnerability is deployed.
hononpmDescription
Hono is a Web application framework that provides support for any JavaScript runtime. Prior to 4.12.25, 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. 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 vulnerability is fixed in 4.12.25.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | hono | all versions | 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. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
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
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-54289 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-54289. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-54289 in your dependencies?
O3 detects CVE-2026-54289 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.