CVE-2026-59897 honojs CVE debrief

Who should care

Users of Hono Web application framework versions between 4.3.3 and 4.12.27 should be aware of this vulnerability and take necessary actions to protect their applications. This includes reviewing and updating middleware or application logic that relies on X-Forwarded-For chain, rate limiting, audit logging, or proxy-chain validation. Additionally, users should monitor for any suspicious activity or incomplete data in logs and security-sensitive components.

Technical summary

The AWS API Gateway v1 adapter in Hono Web application framework versions 4.3.3 to 4.12.27 has a vulnerability that causes it to drop distinct repeated request header values. This occurs because the adapter uses a substring comparison instead of an exact match for de-duplication. As a result, middleware or application logic that depends on the complete X-Forwarded-For chain, rate limiting, audit logging, or proxy-chain validation may receive incomplete data. The issue is fixed in version 4.12.27, and users should review and update affected components to prevent potential data integrity issues.

Defensive priority

Medium priority due to the potential impact on data integrity and security logging. Users should prioritize updating to version 4.12.27 or later and review affected middleware or application logic.

Recommended defensive actions

• Update Hono to version 4.12.27 or later
• Review and update middleware or application logic that relies on X-Forwarded-For chain, rate limiting, audit logging, or proxy-chain validation
• Monitor for any suspicious activity or incomplete data in logs and security-sensitive components
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed
• Check relevant monitoring, detection, and logs for exposed assets that need extra review

Evidence notes

The CVE record was published on 2026-07-08T17:17:27.637Z and was last modified on 2026-07-10T18:01:31.563Z. The NVD entry is currently Awaiting Analysis. The Hono Web application framework has a vulnerability in its AWS API Gateway v1 adapter. From version 4.3.3 to 4.12.27, the adapter can drop distinct repeated request header values due to a substring comparison instead of an exact match. This affects middleware or application logic relying on the complete X-Forwarded-For chain, rate limiting, audit logging, or proxy-chain validation, potentially leading to incomplete data. Evidence is limited to public CVE and NVD information.

Official resources