CVE-2026-39408

Hono is a web framework for JavaScript. Prior to 4.11.4, the JWK/JWKS JWT verification middleware had a flaw that allowed the algorithm from the JWT header to influence signature verification when the selected JWK did not define an algorithm. This could enable JWT algorithm confusion and, in certain configurations, allow forged tokens to be accepted.

Hono is a web framework for JavaScript. Prior to version 4.11.4, the JWT middleware for JWK/JWKS verification had a flaw where the JWT header's alg value could influence signature verification when the selected JWK did not explicitly specify an algorithm. This could enable JWT algorithm confusion and, in certain configurations, allow forged tokens to be accepted.

Path traversal vulnerability in serve-static on Windows via encoded backslash (%5C) in the request path. On Windows hosts, an encoded backslash (%5C) decodes to \, which the Windows path treats as a directory separator.

Hono before version 4.12.34 has a ReDoS vulnerability in the built-in CORS middleware (hono/cors). During a preflight OPTIONS request, the middleware parses the Access-Control-Request-Headers header using a regular expression with quadratic complexity, which can cause long CPU consumption and block request processing. This affects the default configuration when allowHeaders is unset or empty.

A vulnerability in the Hono framework from version 3.8.0 to 4.12.33 affects memo() from hono/jsx, which retains the result of a server-side render and reuses it for later renders with equal props. Request-scoped values read inside the component are not part of the comparison, potentially causing a user to receive HTML rendered for another user's request. The issue is fixed in version 4.12.34.

Hono is a web application framework supporting any JavaScript runtime. From 4.7.0 to 4.12.33, the proxy() function in hono/proxy does not remove response headers named by the origin's Connection header. Per RFC 9110, an intermediary must remove these headers before forwarding, but the function only removes standard hop-by-hop headers, potentially leading to disclosure of internal metadata.

A vulnerability in the Hono framework from version 4.12.0 to 4.12.33 affects the languageDetector middleware, which is vulnerable to algorithmic complexity denial of service when processing a crafted language tag with a large number of hyphen-separated subtags. The normalizeLanguage() function repeatedly calls parts.slice(0, i).join('-') for every possible prefix, causing quadratic processing growth. The issue is fixed in version 4.12.34.

Hono before version 4.11.10 contains a timing attack vulnerability in the basicAuth and bearerAuth middlewares due to non-constant-time string comparison in the timingSafeEqual function. Attackers can exploit early termination of string equality checks to infer valid credentials through precise timing measurements.

A vulnerability in Hono before version 4.12.7 allows the __proto__ key in parseBody with the dot option enabled, permitting specially crafted form field names to create objects with __proto__ properties. When parsed results are merged into regular JavaScript objects using unsafe merge patterns, attackers can exploit this to achieve prototype pollution and modify object behavior.

In Hono framework versions 4.3.3 through 4.12.26, the AWS API Gateway v1 adapter incorrectly de-duplicates header values using substring comparison instead of exact match. This causes distinct repeated header values to be dropped, affecting the completeness of data processed by middleware or application logic.