CVE-2026-22817: Hono JWT Auth Bypass Vulnerability

CVE-2026-22817 Overview

CVE-2026-22817 is a cryptographic vulnerability affecting the Hono Web application framework's JWT verification middleware. The flaw exists in Hono's JWK/JWKS JWT verification implementation, where the JWT header's alg value could influence signature verification when the selected JWK did not explicitly specify an algorithm. This vulnerability enables JWT algorithm confusion attacks and, under certain configurations, allows forged tokens to be accepted by the application.

Hono is a popular Web application framework that provides support for any JavaScript runtime, making this vulnerability particularly impactful for applications relying on JWT-based authentication across various deployment environments.

Critical Impact

Attackers can exploit JWT algorithm confusion to bypass authentication and forge valid tokens, potentially gaining unauthorized access to protected resources and user accounts.

Affected Products

• Hono Web Application Framework versions prior to 4.11.4
• Applications using Hono's JWT middleware with JWK/JWKS verification
• Any JavaScript runtime environment running vulnerable Hono versions

Discovery Timeline

• 2026-01-13 - CVE CVE-2026-22817 published to NVD
• 2026-01-13 - Last updated in NVD database

Technical Details for CVE-2026-22817

Vulnerability Analysis

This vulnerability is classified under CWE-347 (Improper Verification of Cryptographic Signature). The root issue lies in how Hono's JWT middleware handled algorithm selection during signature verification. When a JWK in the JWKS did not explicitly specify an algorithm via the alg property, the middleware would fall back to using the algorithm specified in the JWT header itself.

This behavior creates a classic JWT algorithm confusion attack vector. An attacker could craft a malicious JWT with a manipulated alg header value to exploit this logic, potentially forcing the verification process to use a weaker or incompatible algorithm that the attacker can satisfy. In certain configurations, this could allow completely forged tokens to pass verification and be accepted as legitimate.

Root Cause

The root cause is the absence of explicit algorithm enforcement in the JWT middleware configuration. When the alg option was not required to be explicitly specified, the verification logic could derive the algorithm from the untrusted JWT header values, violating the security principle that cryptographic parameters should never be taken from untrusted input.

Attack Vector

The attack is network-based and requires no authentication or user interaction. An attacker with knowledge of the target's JWT verification configuration can craft a malicious JWT with a forged payload and manipulated algorithm header. By exploiting JWKs that lack explicit algorithm specification, the attacker can influence the verification process to use an algorithm they can satisfy, effectively bypassing signature validation.

The security patch demonstrates the fix by changing the alg parameter from optional to required:

  * @param {object} options - The options for the JWT middleware.
  * @param {SignatureKey} [options.secret] - A value of your secret key.
  * @param {string} [options.cookie] - If this value is set, then the value is retrieved from the cookie header using that value as a key, which is then validated as a token.
- * @param {SignatureAlgorithm} [options.alg=HS256] - An algorithm type that is used for verifying. Available types are `HS256` | `HS384` | `HS512` | `RS256` | `RS384` | `RS512` | `PS256` | `PS384` | `PS512` | `ES256` | `ES384` | `ES512` | `EdDSA`.
+ * @param {SignatureAlgorithm} options.alg - An algorithm type that is used for verifying (required). Available types are `HS256` | `HS384` | `HS512` | `RS256` | `RS384` | `RS512` | `PS256` | `PS384` | `PS512` | `ES256` | `ES384` | `ES512` | `EdDSA`.
  * @param {string} [options.headerName='Authorization'] - The name of the header to look for the JWT token. Default is 'Authorization'.
  * @param {VerifyOptions} [options.verification] - Additional options for JWT payload verification.
  * @returns {MiddlewareHandler} The middleware handler function.

Source: GitHub Commit Update

Additionally, new error types were introduced to handle algorithm-related issues:

 import { signing, verifying } from './jws'
 import type { HonoJsonWebKey, SignatureKey } from './jws'
 import {
+  JwtAlgorithmMismatch,
+  JwtAlgorithmRequired,
   JwtHeaderInvalid,
   JwtHeaderRequiresKid,
   JwtPayloadRequiresAud,

Source: GitHub Commit Update

Detection Methods for CVE-2026-22817

Indicators of Compromise

• JWT tokens with unusual or unexpected alg header values in authentication logs
• Multiple authentication attempts using different algorithm types from the same source
• Successful authentication with tokens that have mismatched algorithm headers compared to expected configuration
• Anomalous JWT payloads that pass verification despite suspicious signatures

Detection Strategies

• Implement logging for all JWT verification attempts including the algorithm specified in the token header
• Monitor for authentication events where the JWT header algorithm differs from the expected server-side configuration
• Set up alerts for rapid succession of authentication attempts with varying algorithm parameters
• Review application dependencies for Hono versions prior to 4.11.4

Monitoring Recommendations

• Enable detailed logging in the JWT middleware to capture algorithm mismatch events
• Monitor authentication success rates for anomalies that could indicate forged token acceptance
• Implement runtime security monitoring to detect unauthorized access patterns following authentication
• Set up dependency scanning to identify vulnerable Hono framework versions in your codebase

How to Mitigate CVE-2026-22817

Immediate Actions Required

• Upgrade Hono to version 4.11.4 or later immediately
• Audit all JWT middleware configurations to ensure the alg option is explicitly specified
• Review authentication logs for any suspicious activity that may indicate prior exploitation
• Regenerate JWT secrets if there is any suspicion of token forgery

Patch Information

The vulnerability is fixed in Hono version 4.11.4. The patch requires the alg option to be explicitly specified in JWT middleware configuration, preventing algorithm confusion by ensuring that the verification algorithm is not derived from untrusted JWT header values.

For detailed patch information, refer to:

• GitHub Commit Update
• GitHub Security Advisory GHSA-f67f-6cw9-8mq4

Workarounds

• If immediate upgrade is not possible, ensure all JWKs in your JWKS explicitly specify the alg property
• Implement additional validation layer to verify JWT header algorithms before processing
• Consider implementing a Web Application Firewall (WAF) rule to reject JWTs with unexpected algorithm values
• Restrict JWT algorithm acceptance to only the specific algorithm your application requires

# Update Hono to patched version
npm update hono@4.11.4

# Or specify exact version in package.json
npm install hono@^4.11.4

# Verify installed version
npm list hono