# CVE-2026-101917: PyJWT JWKS client denial-of-service via cache bypass

Source: https://junglewise.ai/threats/cve-2026-101917-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-2026-101917 · Severity: medium · CVSS 5.3 · Published 2026-09-28

PyJWT is a Python library that validates JSON Web Tokens used for API authentication and secure communications. An attacker can exploit a caching flaw to force repeated requests to an external JWKS endpoint by repeatedly sending tokens with unknown or varying key identifiers, amplifying outbound traffic and potentially causing denial-of-service against the JWKS server or the application itself.

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-2026-101917 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-101917 being exploited in the wild.

**How severe is CVE-2026-101917?** Medium severity, with a CVSS score of 5.3, published 28 September 2026.

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

**Is there a fix for CVE-2026-101917?** 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-2026-101917 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-101917?** 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 PyJWKClient get_signing_key_from_jwt function failed to throttle cache misses for unknown key identifiers (kid), allowing attackers to craft repeated authentication requests that bypass the JWKS cache and trigger excessive refresh operations. This occurs because the client lacked a negative cache or minimum refresh interval for unknown keys, enabling traffic amplification attacks against the remote JWKS endpoint.

## Affected products

- jpadilla PyJWT prior to 2.14.0

## Identifiers

- CVE-2026-101917
- GHSA-2gx3-rcp4-g85q
- PYSEC-2026-4140

## Timeline

- 2026-09-28: disclosed: CVE-2026-101917 published
- 2026-09-11: patched: Fix released in version 2.14.0

## References

- [https://github.com/jpadilla/pyjwt/commit/ba4853a75fb9676362da17f67d0f64bd18afd4e1](https://github.com/jpadilla/pyjwt/commit/ba4853a75fb9676362da17f67d0f64bd18afd4e1)
- [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)