PyJWT: Algorithm allow-list bypass when decoding with PyJWK / PyJWKClient keys

Exploitation

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

CVSS

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

EPSS

• CVE-2026-48523: 0.13% estimated exploitation activity in the next 30 days; percentile 2.36 (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.

[!NOTE] Scored assuming a deployment where algorithm policy functions as an authentication/authorization boundary. In deployments where the algorithm policy enforces crypto agility only, the practical confidentiality impact is lower and the issue is closer to an integrity-of-policy-enforcement bug. PyJWT 2.9.0 through 2.12.1 allows a verifier-side algorithm allow-list bypass when jwt.decode() or jwt.decodecomplete() are called with a PyJWK key. The token header alg is checked against the caller-supplied algorithms allow-list, but signature verification is performed with the algorithm bound to the PyJWK object instead of the header algorithm. An attacker who controls a registered JWK/JWKS private key can sign with a disallowed algorithm, advertise an allowed algorithm in the JWT header, and still be accepted. The issue affects the documented PyJWKClient.getsigningkeyfromjwt(...) flow. Summary PyJWT's PyJWK verification path allows a verifier-side algorithm allow-list bypass. In…

Published by the source

15 Jun 2026, 19:27 UTC

Last modified by the source

10 Sep 2026, 03:51 UTC

Source last checked

26 Oct 2026, 13:45 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-jq35-7prp-9v3f

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-jq35-7prp-9v3f

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# Patch Next advisory brief: CVE-2026-48523

Advisory: PyJWT: Algorithm allow-list bypass when decoding with `PyJWK` / `PyJWKClient` keys
IDs: CVE-2026-48523, GHSA-jq35-7prp-9v3f
Record: https://patchnext.com/advisories/cve-2026-48523 (revision 2, source checked 26 Oct 2026, 13:45 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: pyjwt 2.13.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI pyjwt: affected >= 2.9.0, < 2.13.0; fixed in 2.13.0

## Suggested inspection (read-only)
- `python -m pip show pyjwt`: 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 pyjwt.
- 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-jq35-7prp-9v3f (OSV record GHSA-jq35-7prp-9v3f lists affected ranges: PyPI pyjwt >=2.9.0 <2.13.0 (fixed))
- Verified: https://github.com/advisories/GHSA-jq35-7prp-9v3f (GitHub-reviewed advisory GHSA-jq35-7prp-9v3f lists affected ranges: PyPI pyjwt >=2.9.0 <2.13.0)

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