CVE-2025-71381

Hono before 4.10.3 contains a flaw in its CORS middleware: when the origin is not set to "*", the middleware copies the Vary header from the incoming request into the response. Because Vary is a response header that should be managed by the server, an attacker can supply arbitrary Vary values that are reflected into the response, potentially causing cache key pollution and inconsistent CORS enforcement in environments that rely on shared caches or proxies.

Hono before 4.10.3 contains a flaw in its CORS middleware: when the origin is not set to "*", the middleware copies the Vary header from the incoming request into the response. Because Vary is a response header that should be managed by the server, an attacker can supply arbitrary Vary values that are reflected into the response, potentially causing cache key pollution and inconsistent CORS enforcement in environments that rely on shared caches or proxies.

Duplicate Advisory

This advisory has been withdrawn because it is a duplicate of GHSA-q7jf-gf43-6x6p. This link is maintained to preserve external references.

Original Description

Hono before 4.10.2 (fixed in 4.10.3) contains a flaw in its CORS middleware: when the origin is not set to "*", the middleware copies the Vary header from the incoming request into the response. Because Vary is a response header that should be managed by the server, an attacker can supply arbitrary Vary values that are reflected into the response, potentially causing cache key pollution and inconsistent CORS enforcement in environments that rely on shared caches or proxies.

Summary

A flaw in the CORS middleware allowed request Vary headers to be reflected into the response, enabling attacker-controlled Vary values and potentially affecting cache behavior.

Details

The middleware previously copied the Vary header from the request when origin was not set to "*". Since Vary is a response header that should only be managed by the server, this could allow an attacker to influence caching behavior or cause inconsistent CORS handling.

Most environments will see impact only when shared caches or proxies rely on the Vary header. The practical effect varies by configuration.

Impact

May cause cache key pollution and inconsistent CORS enforcement in certain setups. No direct confidentiality, integrity, or availability impact in default configurations.

Resolution

Update to the latest patched release. The CORS middleware has been corrected to handle Vary exclusively as a response header.

Hono before 4.10.3 contains a flaw in its CORS middleware: when the origin is not set to "*", the middleware copies the Vary header from the incoming request into the response. Because Vary is a response header that should be managed by the server, an attacker can supply arbitrary Vary values that are reflected into the response, potentially causing cache key pollution and inconsistent CORS enforcement in environments that rely on shared caches or proxies.

Hono before 4.10.3 contains a flaw in its CORS middleware: when the origin is not set to "*", the middleware copies the Vary header from the incoming request into the response. Because Vary is a response header that should be managed by the server, an attacker can supply arbitrary Vary values that are reflected into the response, potentially causing cache key pollution and inconsistent CORS enforcement in environments that rely on shared caches or proxies.

Duplicate Advisory

This advisory has been withdrawn because it is a duplicate of GHSA-q7jf-gf43-6x6p. This link is maintained to preserve external references.

Original Description

Hono before 4.10.2 (fixed in 4.10.3) contains a flaw in its CORS middleware: when the origin is not set to "*", the middleware copies the Vary header from the incoming request into the response. Because Vary is a response header that should be managed by the server, an attacker can supply arbitrary Vary values that are reflected into the response, potentially causing cache key pollution and inconsistent CORS enforcement in environments that rely on shared caches or proxies.

Summary

A flaw in the CORS middleware allowed request Vary headers to be reflected into the response, enabling attacker-controlled Vary values and potentially affecting cache behavior.

Details

The middleware previously copied the Vary header from the request when origin was not set to "*". Since Vary is a response header that should only be managed by the server, this could allow an attacker to influence caching behavior or cause inconsistent CORS handling.

Most environments will see impact only when shared caches or proxies rely on the Vary header. The practical effect varies by configuration.

Impact

May cause cache key pollution and inconsistent CORS enforcement in certain setups. No direct confidentiality, integrity, or availability impact in default configurations.

Resolution

Update to the latest patched release. The CORS middleware has been corrected to handle Vary exclusively as a response header.