CVE-2026-59897: Hono: API Gateway v1 adapter can drop a distinct repeated request header value during de-duplication
Summary
The AWS API Gateway v1 adapter can drop a distinct repeated request header value. When a header appears multiple times, the adapter de-duplicates values using a substring comparison instead of an exact match, so a value that is a substring of another value of the same header is omitted (for example, 203.0.113.1 is dropped when another value is 203.0.113.10).
Details
A repeated request header carries an ordered list of values. Middleware or application logic that depends on the complete list — such as IP restriction that walks the X-Forwarded-For chain, rate limiting, audit logging, or proxy-chain validation — can therefore receive incomplete data that differs from what the client actually sent.
This issue arises on deployments using the AWS API Gateway v1 adapter (the same pattern also affects the VPC Lattice adapter), for requests that contain the same header more than once.
Impact
An attacker can craft repeated header values so that one value is omitted before the application sees the request. Where a security or routing decision relies on the full chain, this can alter that decision.
This affects applications deployed through Hono's AWS API Gateway v1 (or VPC Lattice) adapter that rely on the complete set of repeated request header values.
Other sources
Hono is a Web application framework that provides support for any JavaScript runtime. From 4.3.3 before 4.12.27, the AWS API Gateway v1 adapter can drop a distinct repeated request header value because it de-duplicates values using a substring comparison instead of an exact match, so middleware or application logic that depends on the complete X-Forwarded-For chain, rate limiting, audit logging, or proxy-chain validation can receive incomplete data. This issue is fixed in version 4.12.27.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
npm/honoto a version that resolves this vulnerability.Fixed in 4.12.27 - Upgrade
Upgrade
Hono (AWS API Gateway v1 adapter)to a version that resolves this vulnerability.Fixed in 4.12.27
Event History
Frequently Asked Questions
What is the severity of CVE-2026-59897?
The severity of CVE-2026-59897 is rated as medium with a score of 4.8.
How do I fix CVE-2026-59897?
To fix CVE-2026-59897, update to Hono version 4.12.27 or later.
What is the risk level of CVE-2026-59897?
CVE-2026-59897 has a risk level of 32.
What type of application does CVE-2026-59897 affect?
CVE-2026-59897 affects Hono, a web application framework for JavaScript runtimes.
What issue does CVE-2026-59897 address?
CVE-2026-59897 addresses an issue where the AWS API Gateway v1 adapter drops distinct repeated request header values during de-duplication.