Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to 1.9.0, the default RFC 7523 JWTBearerGrant.get_audiences() returns an empty list, causing JWTBearerGrant.verify_claims() to require only that an aud claim exists without matching the current authorization server. An attacker holding a legitimate assertion for another service can present it to a server that shares the signing key and uses the default grant, obtaining an access token across a trust boundary.
Implementations that override get_audiences() with the server's valid audience identifiers are not affected. This issue is fixed in version 1.9.0.
Attack Parameters
Attack Vector
Network
Can be exploited remotely
Attack Complexity
High
Difficult to exploit
Privileges Required
Low
Basic privileges needed
User Interaction
None
No user interaction needed
Impact Assessment
Confidentiality
High
Complete data leak
Integrity
High
Complete data modification
Availability
None
No disruption
CVSS Vector v3.1
Weakness Type (CWE)
References 4
https://github.com/authlib/authlib/commit/e3bd41cb29dcfee434453b135ffb487884bae…
security-advisories@github.com
https://github.com/authlib/authlib/pull/945
security-advisories@github.com
https://github.com/authlib/authlib/releases/tag/v1.9.0
security-advisories@github.com
https://github.com/authlib/authlib/security/advisories/GHSA-fch4-3c6x-j4gc
security-advisories@github.com