# CVE-2026-102265: PyJWT denial of service via deeply nested token headers

Source: https://junglewise.ai/threats/cve-2026-102265-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-2026-102265 · Severity: medium · CVSS 5.3 · Published 2026-09-28

PyJWT is a Python library that processes JSON Web Tokens, which are widely used for authentication in web applications. A flaw in versions 2.13.0 through 2.13.x allows an attacker to send a malformed token with deeply nested header fields, causing the server to crash with an unhandled error and return an HTTP 500 response. This creates a denial-of-service condition affecting any application using the vulnerable library versions.

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

## Quick answers

**Is CVE-2026-102265 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-102265 being exploited in the wild.

**How severe is CVE-2026-102265?** Medium severity, with a CVSS score of 5.3, published 28 September 2026.

**Which products and versions are affected?** PyJWT 2.13.0 to 2.13.x; pyjwt (PyPI) >= 2.13.0, < 2.14.0, ECOSYSTEM:introduced=2.13.0,fixed=2.14.0.

**Is there a fix for CVE-2026-102265?** 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-2026-102265 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-102265?** Check whether you run 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 PyJWS._load (jwt/api_jws.py) where the JSON parser can raise a RecursionError on deeply nested structures, but the error handler only catches ValueError. An unauthenticated attacker can supply a malformed token with recursive header nesting to trigger the unhandled RecursionError, escaping PyJWT's documented error hierarchy. The fix, released in version 2.14.0, adds proper handling for RecursionError during token parsing.

## Affected products

- PyJWT PyJWT 2.13.0 to 2.13.x

## Identifiers

- CVE-2026-102265
- GHSA-8wjv-2p76-3863
- PYSEC-2026-4142

## Timeline

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

## References

- [https://github.com/jpadilla/pyjwt/commit/06573692ebcdec8831c3927513b3e87c31fbbb62](https://github.com/jpadilla/pyjwt/commit/06573692ebcdec8831c3927513b3e87c31fbbb62)
- [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)