CVE-2024-41949 in biscuit-rust
Summary
by MITRE • 08/02/2024
biscuit-rust is the Rust implementation of Biscuit, an authentication and authorization token for microservices architectures. 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, which includes the public key of the previous block (used in the signature) and 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.
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Analysis
by VulDB Data Team • 08/09/2024
The vulnerability in biscuit-rust identified as CVE-2024-41949 represents a critical flaw in the authentication and authorization token system designed for microservices architectures. This implementation of Biscuit allows for the generation of third-party blocks without requiring the complete token to be transmitted to external authorities, which is intended to enhance performance and reduce bandwidth usage in distributed systems. The system operates by enabling third-party authorities to create new blocks using only the essential information needed for signature generation, specifically including the public key from the previous block and the public keys stored in the token's symbol table for datalog expression internment. This design approach aims to maintain security while optimizing token processing in microservice environments where traditional full-token transmission would be inefficient.
The technical flaw manifests when malicious actors craft forged third-party block requests that manipulate the public key information provided to the third-party authority. This vulnerability stems from insufficient validation of the key material supplied in the ThirdPartyBlock request, allowing attackers to substitute their own public keys for those belonging to legitimate parties within the token's symbol table. The forged requests can trick the third-party authority into generating signatures that incorrectly trust the malicious keypair rather than the legitimate one, effectively compromising the token's integrity and authorization guarantees. This flaw directly impacts the cryptographic security model of the system by enabling attackers to manipulate the trust relationships established within the datalog expressions that govern access control decisions.
The operational impact of this vulnerability extends beyond simple authentication bypasses, as it fundamentally undermines the trust model that Biscuit relies upon for secure microservice communication. When a third-party authority generates a block using compromised key information, the resulting token becomes vulnerable to unauthorized access and privilege escalation attacks. The consequences include potential data breaches, unauthorized service access, and the complete subversion of authorization policies that should protect microservice boundaries. Attackers could leverage this vulnerability to impersonate legitimate services, gain access to restricted resources, or manipulate access control decisions within the distributed system architecture. This represents a significant risk in environments where Biscuit tokens are used to secure inter-service communications and enforce access control policies across multiple microservices.
Mitigation strategies for CVE-2024-41949 should focus on implementing robust input validation and key material verification mechanisms within the third-party block generation process. The system must validate that the public keys provided in ThirdPartyBlock requests match expected values from the token's symbol table and implement cryptographic checks to prevent key substitution attacks. Organizations should consider updating to patched versions of biscuit-rust that address the validation gap in third-party block processing, while also implementing monitoring systems to detect anomalous third-party block generation patterns. The fix should incorporate proper key fingerprint verification and ensure that third-party authorities only generate blocks using verified key material from the original token. This vulnerability aligns with CWE-295 which addresses improper certificate validation and relates to ATT&CK technique T1550.003 for use of valid credentials, as it enables attackers to manipulate the credential trust relationships within the authorization token system.