CVE-2026-48523

PyJWT: Algorithm allow-list bypass when decoding with `PyJWK` / `PyJWKClient` keys

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.

Scores

Weaknesses (CWE)

• CWE-347

Advisories

• GHSA-jq35-7prp-9v3f — PyJWT: Algorithm allow-list bypass when decoding with `PyJWK` / `PyJWKClient` keys
• PYSEC-2026-176 — 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_c

European references

• ENISA EUVD · EUVD-2026-32918
• GCVE · GCVE-0-2026-48523

CERT-FR advisories

• CERTFR-2026-AVI-1385 — Multiples vulnérabilités dans les produits VMware · cert.ssi.gouv.fr
• CERTFR-2026-AVI-1366 — Multiples vulnérabilités dans les produits Splunk · cert.ssi.gouv.fr
• CERTFR-2026-AVI-0933 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr

Affected configurations (NVD CPE)

• cpe:2.3:a:pyjwt_project:pyjwt:*:*:*:*:*:*:*:* ≥ 2.9.0 < 2.13.0

Affected products

References

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

Sources