CVE-2026-54289

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.

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.

CVE-2026-54289 has a CVSS score of 4.8 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.12.25); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-54289? CVE-2026-54289 is a medium-severity security vulnerability in hono (npm), affecting versions < 4.12.25. It is fixed in 4.12.25.
2. How severe is CVE-2026-54289? CVE-2026-54289 has a CVSS score of 4.8 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of hono are affected by CVE-2026-54289? hono (npm) versions < 4.12.25 is affected.
4. Is there a fix for CVE-2026-54289? Yes. CVE-2026-54289 is fixed in 4.12.25. Upgrade to this version or later.
5. Is CVE-2026-54289 exploitable, and should I be worried? Whether CVE-2026-54289 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-54289 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-54289? Upgrade hono to 4.12.25 or later.