Incorrect Behavior Order: Validate Before Canonicalize Affecting pyjwt package, versions [,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-20247706
- published29 Sept 2026
- disclosed28 Sept 2026
- creditze3tar
Introduced: 28 Sep 2026
NewCVE-2026-102269 (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 Incorrect Behavior Order: Validate Before Canonicalize via the _load method in jwt/api_jws.py, which accepts non-canonical base64url-encoded JWS segments. Because the library does not verify that a decoded-then-re-encoded segment round-trips to the original input, an attacker can supply a JWT whose header, payload, or signature segment is a non-canonical base64url encoding that decodes to the same bytes as a legitimate token. This allows the attacker to forge or manipulate tokens in ways that bypass integrity checks, leading to limited confidentiality and integrity impact.