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Vulnerability record · CVE-2026-48523 · published 28 May 2026

CVE-2026-48523: Pyjwt project pyjwt improper verification of cryptographic signature vulnerability

Pyjwt Project · Pyjwt

PyJWT is a JSON Web Token implementation in Python. From 2.9.0 to 2.12.1, there is a verifier-side algorithm allow-list bypass when jwt.decode() or jwt.decode_complete() are called with a PyJWK key. The token header alg is checked against the caller-supplied algorithms allow-list, but signature verification is performed with the algorithm bound to the PyJWK object instead of the header algorithm. An attacker who controls a registered JWK/JWKS private key can sign with a disallowed algorithm, advertise an allowed algorithm in the JWT header, and still be accepted. The issue affects the documented PyJWKClient.get_signing_key_from_jwt(...) flow. This vulnerability is fixed in 2.13.0.

5.4 CVSS 3.1 Medium EPSS 0.17% · top 94.3% CWE-347 · Improper verification of cryptographic signature
5.4CVSS 3.1 base score
0.17%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
2References, 2 tagged exploit
16 Sep 2026Last modified by NVD

Description

PyJWT is a JSON Web Token implementation in Python. From 2.9.0 to 2.12.1, there is a verifier-side algorithm allow-list bypass when jwt.decode() or jwt.decode_complete() are called with a PyJWK key. The token header alg is checked against the caller-supplied algorithms allow-list, but signature verification is performed with the algorithm bound to the PyJWK object instead of the header algorithm. An attacker who controls a registered JWK/JWKS private key can sign with a disallowed algorithm, advertise an allowed algorithm in the JWT header, and still be accepted. The issue affects the documented PyJWKClient.get_signing_key_from_jwt(...) flow. This vulnerability is fixed in 2.13.0.

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

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/jpadilla/pyjwt/security/advisories/GHSA-jq35-7prp-9v3f ExploitVendor Advisory
https://github.com/jpadilla/pyjwt/security/advisories/GHSA-jq35-7prp-9v3f ExploitVendor Advisory

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Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-48523), CISA KEV, FIRST EPSS (scores of 2026-09-28). This page is refreshed as NVD updates the record.