PyJWT: Public keys in DER form are accepted as HMAC secrets, bypassing the CVE-2022-29217 guard

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-2026-102271: 0.21% estimated exploitation activity in the next 30 days; percentile 11.93 (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 HMACAlgorithm.preparekey blocks asymmetric keys from being used as HMAC secrets by searching for text markers only. It looks for -----BEGIN and for an ssh- prefix. The same key in DER form is binary ASN.1 and has neither marker, so it passes the check and is used as an HMAC secret. An application that verifies tokens with an RSA or EC public key, and also allows HS256 with that same key, can be given a forged token. The attacker signs it with the public key, which is public. This is the key confusion problem CVE-2022-29217 was filed for, reachable again through a different encoding. The reach is smaller than the original CVE. The application must already be in that misconfiguration, and it must hold its public key as DER bytes rather than PEM. Details The guard is at jwt/algorithms.py:331: Both helpers are text matchers. Neither one parses the key. - jwt/utils.py:126, ispemformat, runs a regex for ----[- ]BEGIN ...----. - jwt/utils.py:141, issshkey, checks startswith against…

Published by the source

29 Sep 2026, 23:14 UTC

Last modified by the source

1 Oct 2026, 17:55 UTC

Source last checked

26 Oct 2026, 13:54 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-p4g4-x82p-q773

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-p4g4-x82p-q773

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-p4g4-x82p-q773

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# Patch Next advisory brief: CVE-2026-102271

Advisory: PyJWT: Public keys in DER form are accepted as HMAC secrets, bypassing the CVE-2022-29217 guard
IDs: CVE-2026-102271, GHSA-p4g4-x82p-q773
Record: https://patchnext.com/advisories/cve-2026-102271 (revision 3, source checked 26 Oct 2026, 13:54 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: pyjwt 2.14.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI pyjwt: affected >= 2.4.0, < 2.14.0; fixed in 2.14.0

## 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://github.com/advisories/GHSA-p4g4-x82p-q773 (GitHub-reviewed advisory GHSA-p4g4-x82p-q773 lists affected ranges: PyPI pyjwt >=2.4.0 <2.14.0)
- Verified: https://osv.dev/vulnerability/GHSA-p4g4-x82p-q773 (OSV record GHSA-p4g4-x82p-q773 lists affected ranges: PyPI pyjwt >=2.4.0 <2.14.0 (fixed))

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