Executive brief
Hono, a web framework, contains a flaw in its AWS API Gateway and VPC Lattice adapters that can cause certain security information to be ignored. When a request contains multiple headers with similar values, the system may accidentally delete one of them, such as an IP address in a security log. This could allow an attacker to bypass security rules like rate limiting or IP restrictions by tricking the system into seeing an incomplete list of data.
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
Timeline
- 2026-06-23: disclosed: Initial disclosure by yusukebe
- 2026-07-08: advisory: NVD publication
- 2026-07-21: advisory: GitHub Advisory reviewed