CVE-2026-102266: CWE-347: Improper Verification of Cryptographic Signature in jpadilla pyjwt
PyJWT is a Python implementation of JSON Web Token standards. From 2.13.0 until 2.14.0, HMACAlgorithm.from_jwk is affected because PyJWK verification path used the decoded key without applying prepare_key validation. This occurs when a trusted JWK Set contains an oct entry with an empty k value. As a result, an attacker signs an HMAC token with the same zero-length key accepted by PyJWT. Consequently, forged token can carry arbitrary authenticated claims. This issue is fixed in version 2.14.0.
AI Analysis
Technical Summary
PyJWT, a Python library implementing JSON Web Token standards, has a cryptographic signature verification flaw in versions >=2.13.0 and <2.14.0. Specifically, the HMACAlgorithm.from_jwk method does not apply prepare_key validation on the decoded key from a trusted JWK Set. If the JWK Set contains an oct entry with an empty 'k' value, an attacker can sign an HMAC token with a zero-length key that PyJWT accepts as valid. This allows forging tokens with arbitrary authenticated claims. The issue is addressed in version 2.14.0.
Potential Impact
An attacker can forge HMAC tokens with arbitrary authenticated claims by exploiting the acceptance of zero-length keys in the vulnerable versions. This compromises the integrity and authenticity of tokens, potentially allowing unauthorized access or privilege escalation in systems relying on PyJWT for token verification.
Mitigation Recommendations
Upgrade PyJWT to version 2.14.0 or later, where this vulnerability is fixed. No other mitigations are specified. Patch status is confirmed as fixed in 2.14.0.
CVE-2026-102266: CWE-347: Improper Verification of Cryptographic Signature in jpadilla pyjwt
Description
PyJWT is a Python implementation of JSON Web Token standards. From 2.13.0 until 2.14.0, HMACAlgorithm.from_jwk is affected because PyJWK verification path used the decoded key without applying prepare_key validation. This occurs when a trusted JWK Set contains an oct entry with an empty k value. As a result, an attacker signs an HMAC token with the same zero-length key accepted by PyJWT. Consequently, forged token can carry arbitrary authenticated claims. This issue is fixed in version 2.14.0.
CVSS v3.1
Score 7.4high
Affected software
jpadilla
pyjwt
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
PyJWT, a Python library implementing JSON Web Token standards, has a cryptographic signature verification flaw in versions >=2.13.0 and <2.14.0. Specifically, the HMACAlgorithm.from_jwk method does not apply prepare_key validation on the decoded key from a trusted JWK Set. If the JWK Set contains an oct entry with an empty 'k' value, an attacker can sign an HMAC token with a zero-length key that PyJWT accepts as valid. This allows forging tokens with arbitrary authenticated claims. The issue is addressed in version 2.14.0.
Potential Impact
An attacker can forge HMAC tokens with arbitrary authenticated claims by exploiting the acceptance of zero-length keys in the vulnerable versions. This compromises the integrity and authenticity of tokens, potentially allowing unauthorized access or privilege escalation in systems relying on PyJWT for token verification.
Mitigation Recommendations
Upgrade PyJWT to version 2.14.0 or later, where this vulnerability is fixed. No other mitigations are specified. Patch status is confirmed as fixed in 2.14.0.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-09-28T20:11:16.658Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 6abacf14f7a7c541062b9a52
Added to database: 09/28/2026, 20:33:24 UTC
Last enriched: 09/28/2026, 20:47:51 UTC
Last updated: 09/29/2026, 03:33:49 UTC
Views: 9
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