The Omnivore API (packages/api) before the fix in commit abf53d6 contains an authentication bypass in Apple sign-in token verification. The decodeAppleToken function extracted the 'alg' field from the attacker-supplied JWT header and passed it as the sole allowed algorithm to jwt.verify(). Using jsonwebtoken v8 (which does not validate key/algorithm compatibility), an attacker can set alg=HS256 and sign a forged token using Apple's publicly available RSA public key as the HMAC secret, bypassing signature verification and impersonating any Apple-linked account.
Attack Parameters
Attack Vector
Network
Can be exploited remotely
Attack Complexity
Low
Easy to exploit
Attack Requirements
None
No additional conditions
Privileges Required
None
No 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 v4.0
Weakness Type (CWE)
References 4
https://github.com/omnivore-app/omnivore
disclosure@vulncheck.com
https://github.com/omnivore-app/omnivore/commit/abf53d6508755d3d22a994e28e370a9…
disclosure@vulncheck.com
https://github.com/omnivore-app/omnivore/pull/4652
disclosure@vulncheck.com
https://www.vulncheck.com/advisories/omnivore-before-android-0.227.0-authentica…
disclosure@vulncheck.com