Hono JWK Auth Middleware has JWT algorithm confusion when JWK lacks "alg" (untrusted header.alg fallback)

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

8.2 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N

EPSS

• CVE-2026-22818: 0.14% estimated exploitation activity in the next 30 days; percentile 3.17 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary A flaw in Hono’s JWK/JWKS JWT verification middleware allowed the algorithm specified in the JWT header to influence signature verification when the selected JWK did not explicitly define an algorithm. This could enable JWT algorithm confusion and, in certain configurations, allow forged tokens to be accepted. Details When verifying JWTs using JWKs or a JWKS endpoint, the middleware selected the verification algorithm based on the JWK’s alg field if present. If the JWK did not specify an algorithm, the middleware fell back to using the alg value provided in the unverified JWT header. Because the alg field in a JWK is optional and commonly omitted in real-world JWKS configurations, this behavior could allow an attacker to influence which algorithm is used for verification. In some environments, this may result in authentication or authorization bypass through crafted JWTs. The practical impact depends on application configuration, including which algorithms are accepted and…

Published by the source

13 Jan 2026, 21:52 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 12:41 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-3vhc-576x-3qv4

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-3vhc-576x-3qv4

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# Patch Next advisory brief: CVE-2026-22818

Advisory: Hono JWK Auth Middleware has JWT algorithm confusion when JWK lacks "alg" (untrusted header.alg fallback)
IDs: CVE-2026-22818, GHSA-3vhc-576x-3qv4
Record: https://patchnext.com/advisories/cve-2026-22818 (revision 2, source checked 26 Oct 2026, 12:41 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: hono 4.11.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm hono: affected < 4.11.4; fixed in 4.11.4

## Suggested inspection (read-only)
- `npm ls hono --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on hono.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-3vhc-576x-3qv4 (OSV record GHSA-3vhc-576x-3qv4 lists affected ranges: npm hono >=0 <4.11.4 (fixed))
- Verified: https://github.com/advisories/GHSA-3vhc-576x-3qv4 (GitHub-reviewed advisory GHSA-3vhc-576x-3qv4 lists affected ranges: npm hono >=0 <4.11.4)

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