CVE-2024-42350 in biscuit
Summary
by MITRE • 08/05/2024
Biscuit is an authorization token with decentralized verification, offline attenuation and strong security policy enforcement based on a logic language. Third-party blocks can be generated without transferring the whole token to the third-party authority. Instead, a `ThirdPartyBlock` request can be sent, providing only the necessary info to generate a third-party block and to sign it: 1. the public key of the previous block (used in the signature), 2. the public keys part of the token symbol table (for public key interning in datalog expressions). A third-part block request forged by a malicious user can trick the third-party authority into generating datalog trusting the wrong keypair. Tokens with third-party blocks containing `trusted` annotations generated through a third party block request. This has been addressed in version 4 of the specification. Users are advised to update their implementations to conform. There are no known workarounds for this vulnerability.
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Analysis
by VulDB Data Team • 08/05/2024
The vulnerability described in CVE-2024-42350 affects Biscuit authorization tokens, which are designed for decentralized verification and strong security policy enforcement through logic-based languages. This authorization system enables third-party blocks to be generated without requiring the complete token to be transferred to external authorities, relying instead on targeted information exchange. The security mechanism operates through a `ThirdPartyBlock` request that contains specific cryptographic data including the public key from the previous block for signature verification and public keys from the token's symbol table for datalog expression internment. The flaw emerges from insufficient validation of the cryptographic inputs provided during third-party block generation, allowing malicious actors to manipulate the request parameters. When a forged third-party block request is submitted, it can deceive the third-party authority into generating datalog expressions that trust incorrect keypairs, potentially compromising the entire authorization framework.
This vulnerability represents a significant security weakness that directly impacts the integrity and trust model of the Biscuit token system, classified under CWE-224 as "Improper Restriction of Operations within a Single-System" and potentially related to CWE-347 for "Improper Verification of Cryptographic Signature." The attack vector specifically targets the token generation process where third-party authorities are tricked into accepting maliciously crafted cryptographic inputs. The operational impact extends beyond simple authorization bypasses, as compromised third-party blocks with `trusted` annotations can undermine the entire security policy enforcement mechanism. The vulnerability affects the fundamental assumption that third-party authorities operate with correct cryptographic inputs, potentially allowing attackers to inject malicious trust relationships that persist throughout the token's lifecycle.
The security implications of this vulnerability are particularly severe because Biscuit tokens are designed for decentralized verification and offline attenuation, meaning that once compromised, malicious third-party blocks can undermine trust relationships across distributed systems without requiring network connectivity. The vulnerability affects the core cryptographic integrity checks that should prevent unauthorized parties from influencing token behavior through forged block generation requests. This weakness creates a potential pathway for attackers to manipulate authorization policies and bypass security constraints that should remain immutable. The affected system architecture relies on the assumption that third-party authorities will correctly validate all inputs, but the vulnerability demonstrates that this assumption can be violated through careful manipulation of the cryptographic parameters submitted in third-party block requests.
Mitigation efforts must focus on updating implementations to version 4 of the Biscuit specification, which addresses the cryptographic validation gaps in third-party block generation. Organizations should immediately assess their current Biscuit implementations to identify any systems still operating under vulnerable versions. The vulnerability's nature precludes standard workarounds since it fundamentally relates to the cryptographic validation process during block generation rather than operational configuration. Security teams should implement monitoring for unauthorized third-party block requests and consider revoking tokens that may have been compromised through this vulnerability. The remediation process requires comprehensive testing of all third-party authority implementations to ensure that cryptographic input validation properly prevents malicious manipulation of public key references in datalog expressions. Additionally, organizations should review their token lifecycle management processes to ensure that tokens with potentially compromised third-party blocks are properly identified and handled according to established security protocols.