Quick answers
- Is CVE-2026-59897 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-59897 being exploited in the wild.
- How severe is CVE-2026-59897?
- Medium severity, with a CVSS score of 4.8, published 8 July 2026.
- Which products and versions are affected?
- hono (npm) >= 4.3.3, < 4.12.27, SEMVER:introduced=4.3.3,fixed=4.12.27.
- Is there a fix for CVE-2026-59897?
- Yes. hono (npm): upgrade to 4.12.27 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-59897 attacked?
- It is attacked over the network, in a software library.
- Am I affected by CVE-2026-59897?
- Check whether you run hono (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
How to fix
- hono (npm): upgrade to 4.12.27 or later
npm install hono@4.12.27
Technical details
A vulnerability exists in Hono's AWS API Gateway v1 and VPC Lattice adapters where repeated request headers are de-duplicated using substring comparison instead of exact matching. For example, if a header contains both '203.0.113.1' and '203.0.113.10', the former is dropped because it is a substring of the latter. This flaw affects middleware or application logic relying on the full header chain, such as X-Forwarded-For for IP restriction, rate limiting, or audit logging. An attacker can craft specific header values to ensure critical values are omitted before the application processes the request. The issue is fixed in version 4.12.27.
Affected products
- honojs hono >= 4.3.3, < 4.12.27
Identifiers
- CVE-2026-59897
- GHSA-xgm2-5f3f-mvvc
Timeline
- 2026-06-23: disclosed: Initial disclosure by yusukebe
- 2026-07-08: advisory: NVD publication
- 2026-07-21: advisory: GitHub Advisory reviewed