Incorrect Behavior Order: Validate Before Canonicalize in pyjwt - #VU150520
Published: September 17, 2026
Vulnerability identifier: #VU150520
CSH Severity: Medium
CVSS v4: 6.3 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N]
CVE-ID: N/A
CWE-ID: CWE-180
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to bypass token revocation controls.
The vulnerability exists due to incorrect behavior order: validate before canonicalize in compact JWS signature-segment decoding when processing a compact JWS with a non-canonical signature segment. A remote attacker can append non-Base64URL characters to a valid token\'s signature segment to bypass token revocation controls.
Exploitation requires an application to use the raw serialized token as the identity for revocation, replay, rate-limit, or cache state.
Affected software
pyjwt
Remediation
Install security update from vendor's website.
pyjwt - update to 2.14.0