# CVE-2026-102269: PyJWT signature validation bypass via non-canonical Base64URL

Source: https://junglewise.ai/threats/cve-2026-102269-pyjwt-is-a-python-implementation-of-json-web-token-standards  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-28. Updated: 2026-09-28  
License: CC BY 4.0 with a link back

CVE-2026-102269 · Severity: medium · CVSS 4.8 · Published 2026-09-28

PyJWT is a Python library for handling JSON Web Tokens, which are used to authenticate and verify secure communications in applications. A vulnerability in versions before 2.14.0 allows attackers to bypass token revocation checks by appending non-standard Base64URL characters to a valid token signature. This enables an attacker to reuse revoked tokens or forge tokens that should have been rejected, potentially leading to unauthorized access.

Technologies: [Jpadilla PyJWT](https://junglewise.ai/threats/technologies/pyjwt), [pyjwt (PyPI)](https://junglewise.ai/threats/technologies/pypi-pyjwt). Vendors: [Jpadilla](https://junglewise.ai/threats/vendors/jpadilla), [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-102269 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-102269 being exploited in the wild.

**How severe is CVE-2026-102269?** Medium severity, with a CVSS score of 4.8, published 28 September 2026.

**Which products and versions are affected?** Jpadilla PyJWT before 2.14.0; pyjwt (PyPI) <= 2.13.0, ECOSYSTEM:introduced=0,fixed=2.14.0.

**Is there a fix for CVE-2026-102269?** Yes. pyjwt (PyPI): upgrade to 2.14.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-102269 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-102269?** Check whether you run Jpadilla PyJWT or pyjwt (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- pyjwt (PyPI): upgrade to 2.14.0 or later

  ```sh
  pip install "pyjwt>=2.14.0"
  ```


## Technical details

The vulnerability exists in the base64url_decode function, which accepts non-canonical Base64URL characters in the signature segment of compact JWS tokens. By appending extra characters to a valid signature, an attacker can create multiple serialized representations that decode to the same bytes, bypassing raw-token revocation checks that compare serialized forms. The fix in 2.14.0 enforces strict canonical Base64URL validation.

## Affected products

- jpadilla PyJWT before 2.14.0

## Identifiers

- CVE-2026-102269
- GHSA-hxm8-2xgr-2p9m
- PYSEC-2026-4147

## Timeline

- 2026-09-28: disclosed
- 2026-09-11: patched: Fixed in version 2.14.0

## References

- [https://github.com/jpadilla/pyjwt/commit/e6f48401001609a8f99e71fcaf355fb895d508a8](https://github.com/jpadilla/pyjwt/commit/e6f48401001609a8f99e71fcaf355fb895d508a8)
- [https://github.com/jpadilla/pyjwt/releases/tag/2.14.0](https://github.com/jpadilla/pyjwt/releases/tag/2.14.0)

## Related threats

- [PyJWT HS256/384/512 token forgery via empty HMAC key in oct JWK](https://junglewise.ai/threats/pyjwt-hs256-384-512-verify-accepts-empty-hmac-key-via-oct-jwk-pyjwk-a3ba63d2)
- [PyJWT decode() options-dict mutation enabling claim-verification bypass](https://junglewise.ai/threats/cve-2026-103001-pyjwt-decode-reintroduces-options-dict-mutation-enabling-silent)
- [PyJWT OKP algorithm key validation bypass](https://junglewise.ai/threats/cve-2026-102275-pyjwt-is-a-python-implementation-of-json-web-token-standards)
- [PyJWT unhandled ValueError in JWK Set parsing](https://junglewise.ai/threats/cve-2026-102274-pyjwt-is-a-python-implementation-of-json-web-token-standards)
- [PyJWT HMAC key validation bypass in HMACAlgorithm.prepare_key](https://junglewise.ai/threats/cve-2026-102273-pyjwt-is-a-python-implementation-of-json-web-token-standards)