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.

Affected: crates.io: biscuit-auth

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:

- the public key of the previous block (used in the signature) - 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.

Consider the following example (nominal case)

- Authority `A` emits the following token: `check if thirdparty("b") trusting ${pubkeyB}` - The well-behaving holder then generates a third-party block request based on the token and sends it to third-party authority `B` - Third-party `B` generates the following third-party block `thirdparty("b"); check if thirdparty("c") trusting ${pubkeyC}` - The token holder now must obtain a third-party block from third party `C` to be able to use the token

Now, with a malicious user: - Authority `A` emits the following token: `check if thirdparty("b") trusting ${pubkeyB}` - The holder then attenuates the token with the following third party block `thirdparty("c")`, signed with a keypair `pubkeyD, privkeyD)` they generate - The holder then generates a third-party block request based on this token, but alter the `ThirdPartyBlockRequest` `publicKeys` field and replace `pubkeyD` with `pubkeyC` - Third-party `B`…

Affected: Hackage: biscuit-haskell

# Public key confusion in third-party blocks

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:

- the public key of the previous block (used in the signature); - the public keys part of the token symbol table (for public key interning in datalog expressions).

A third-party block request forged by a malicious user can trick the third-party authority into generating datalog trusting the wrong keypair.