---
title: "CVE-2026-102266: PyJWT - Authentication Bypass"
description: "PyJWT 2.13.0 to < 2.14.0 contains a broken authentication caused by missing prepare_key validation in HMACAlgorithm.from_jwk, letting attackers forge HMAC tokens with zero-length keys, exploit requires crafted JWK Set with empty key."
url: https://panop.io/threat-heartbeat/CVE-2026-102266/
---

# CVE-2026-102266 PyJWT - Authentication Bypass

PyJWT 2.13.0 to < 2.14.0 contains a broken authentication caused by missing prepare\_key validation in HMACAlgorithm.from\_jwk, letting attackers forge HMAC tokens with zero-length keys, exploit requires crafted JWK Set with empty key.

CVSS base score 7.4 /10

High

CISA KEV

Not listed

Public exploit

Proof of concept available

EPSS

0.18% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-102266)

## Details

Type

Authentication Bypass

Impact

Broken Authentication

CVSS vector

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

Published

28 September 2026

Updated

15 October 2026

Weakness

[CWE-347](https://cwe.mitre.org/data/definitions/347.html)

## Vendor fix

Upgrade to version 2.14.0 or later.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-102266](https://nvd.nist.gov/vuln/detail/CVE-2026-102266)
- [https://github.com/jpadilla/pyjwt/releases/tag/2.14.0](https://github.com/jpadilla/pyjwt/releases/tag/2.14.0)
- [https://github.com/jpadilla/pyjwt/security/advisories/GHSA-9j54-fg26-wv3r](https://github.com/jpadilla/pyjwt/security/advisories/GHSA-9j54-fg26-wv3r)
- [https://github.com/jpadilla/pyjwt/commit/f91ed44dd65baaf457f4b3353ed35e98a753934c](https://github.com/jpadilla/pyjwt/commit/f91ed44dd65baaf457f4b3353ed35e98a753934c)

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## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

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