Improper Verification of Cryptographic Signature Affecting pyjwt package, versions [2.13.0,2.14.0)
Threat Intelligence
Snyk has a proof-of-concept or detailed explanation of how to exploit this vulnerability.
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-PYTHON-PYJWT-20250948
- published29 Sept 2026
- disclosed28 Sept 2026
- creditYuSung Han
Introduced: 28 Sep 2026
NewCVE-2026-102266 (opens in a new tab)How to fix?
Upgrade PyJWT to version 2.14.0 or higher.
Overview
PyJWT is a Python implementation of RFC 7519.
Affected versions of this package are vulnerable to Improper Verification of Cryptographic Signature via the _verify_signature method in jwt/api_jws.py when a PyJWK object is used to verify an HMAC-signed token. In the vulnerable code path, key.key is used directly without passing it through alg_obj.prepare_key(), which means the minimum HMAC key-length check is bypassed. An attacker can supply a weak or undersized HMAC key that would normally be rejected, potentially forging or accepting invalid signatures and compromising both confidentiality and integrity.
Note: This is only exploitable when a PyJWK object is passed directly to the verification call, as the minimum HMAC key-length check does not reject the key under the default configuration in that code path.