Authlib accepts an empty HMAC key, allowing JWS/JWT signature forgery (HS256/HS384/HS512)

Exploitation

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

CVSS

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

EPSS

• CVE-2026-114616: 0.30% estimated exploitation activity in the next 30 days; percentile 22.64 (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.

Reporter: Cavan Loughran, Celvex Group Inc. Summary Authlib's symmetric (oct) key handling accepts an empty key (empty bytes b'' / empty string '') as a valid HMAC signing and verification key. An empty HMAC key produces a deterministic digest that any party can reproduce, so an attacker who knows (or can cause) the application to verify a token with an empty key can forge arbitrary tokens that pass HS256/HS384/HS512 signature verification. This is the Authlib member of the cross-language empty-HMAC-key family already assigned CVE-2026-44351 (fast-jwt, npm) and CVE-2026-45363 (ruby-jwt, RubyGems). This is DISTINCT from Authlib's existing recent JWT-verification advisories. It is not closed by CVE-2026-27962 / GHSA-wvwj-cvrp-7pv5 (JWS JWK header injection, the key=None case), nor by CVE-2026-28802 / GHSA-7wc2-qxgw-g8gg (alg:none blank-signature bypass), nor by GHSA-5357-c2jx-v7qh (algorithm confusion with asymmetric public keys). Those address header-driven key injection, the none…

Published by the source

27 Oct 2026, 16:09 UTC

Last modified by the source

30 Oct 2026, 10:10 UTC

Source last checked

31 Oct 2026, 06:15 UTC

1. Revision 4 · amended · 31 Oct 2026

   Amended from osv record PYSEC-2026-4356

2. Revision 3 · amended · 31 Oct 2026

   Amended from osv record GHSA-8m4g-j4wp-wgcg

3. Revision 2 · amended · 28 Oct 2026

   Amended from osv record GHSA-8m4g-j4wp-wgcg

4. Revision 1 · created · 27 Oct 2026

   Published from ghsa record GHSA-8m4g-j4wp-wgcg

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# Patch Next advisory brief: CVE-2026-114616

Advisory: Authlib accepts an empty HMAC key, allowing JWS/JWT signature forgery (HS256/HS384/HS512)
IDs: CVE-2026-114616, GHSA-8m4g-j4wp-wgcg
Record: https://patchnext.com/advisories/cve-2026-114616 (revision 4, source checked 31 Oct 2026, 06:15 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: authlib 1.9.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI authlib: affected < 1.9.1; fixed in 1.9.1

## Suggested inspection (read-only)
- `python -m pip show authlib`: prints the installed version. Run with the environment that serves production active.

## 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 authlib.
- 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-8m4g-j4wp-wgcg (OSV record GHSA-8m4g-j4wp-wgcg lists affected ranges: PyPI authlib >=0 <1.9.1 (fixed))
- Verified: https://github.com/advisories/GHSA-8m4g-j4wp-wgcg (GitHub-reviewed advisory GHSA-8m4g-j4wp-wgcg lists affected ranges: PyPI authlib >=0 <1.9.1)
- Verified: https://osv.dev/vulnerability/PYSEC-2026-4356 (OSV record PYSEC-2026-4356 lists affected ranges: PyPI authlib >=0 <1.9.1 (fixed))

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