PyJWT: Non-canonical signature segments enable raw-token revocation bypass

Exploitation

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

CVSS

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

EPSS

• CVE-2026-102269: 0.22% estimated exploitation activity in the next 30 days; percentile 13.05 (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 PyJWT 2.13.0 accepts compact JWS signature segments containing characters that are not in the Base64URL alphabet. Appending !!!! to a valid signature does not change the decoded signature bytes or authenticated claims, but it changes the serialized token and its SHA-256 hash. An application that indexes logout or revocation state by the raw token therefore rejects the logged-out token and accepts its no-key alternate serialization. This report separates two issues: permissive compact-JWS decoding is the library behavior, while using raw serialized JWT text as a security identity is a dangerous application composition. A jti-indexed control blocks both representations. Affected Version Confirmed with PyJWT 2.13.0 on CPython 3.13. The mutation changes only the signature segment and requires no signing key. End-to-End Reproduction The loopback-only lab performs: 1. Issue a valid HS256 admin token. 2. Access /protected successfully. 3. Log out the canonical token and store…

Published by the source

29 Sep 2026, 23:17 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-hxm8-2xgr-2p9m

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-hxm8-2xgr-2p9m

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-hxm8-2xgr-2p9m

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# Patch Next advisory brief: CVE-2026-102269

Advisory: PyJWT: Non-canonical signature segments enable raw-token revocation bypass
IDs: CVE-2026-102269, GHSA-hxm8-2xgr-2p9m
Record: https://patchnext.com/advisories/cve-2026-102269 (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: Medium (CVSS 4.8)
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 <= 2.13.0; 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-hxm8-2xgr-2p9m (GitHub-reviewed advisory GHSA-hxm8-2xgr-2p9m lists affected ranges: PyPI pyjwt >=0 <=2.13.0)
- Verified: https://osv.dev/vulnerability/GHSA-hxm8-2xgr-2p9m (OSV record GHSA-hxm8-2xgr-2p9m lists affected ranges: PyPI pyjwt >=0 <2.14.0 (fixed))

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