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EUVD-2026-232696

fkie_cve-2022-31053

Biscuit is an authentication and authorization token for microservices architectures. The Biscuit specification version 1 contains a vulnerable algorithm that allows malicious actors to forge valid Γ-signatures. Such an attack would allow an attacker to create a token with any access level. The version 2 of the specification mandates a different algorithm than gamma signatures and as such is not affected by this vulnerability. The Biscuit implementations in Rust, Haskell, Go, Java and Javascript all have published versions following the v2 specification. There are no known workarounds for this issue.

GHSA-75rw-34q6-72cr — Signature forgery in Biscuit

Affected: crates.io: biscuit-auth, Go: github.com/biscuit-auth/biscuit-go, Maven: com.clever-cloud:biscuit-java

### Impact

The paper [Cryptanalysis of Aggregate Γ-Signature and Practical Countermeasures in Application to Bitcoin](https://eprint.iacr.org/2020/1484) defines a way to forge valid Γ-signatures, an algorithm that is used in the Biscuit specification version 1. It would allow an attacker to create a token with any access level.

As Biscuit v1 was still an early version and not broadly deployed, we were able to contact all known users of Biscuit v1 and help them migrate to Biscuit v2. We are not aware of any active exploitation of this vulnerability.

### Patches

The version 2 of the specification mandates a different algorithm than gamma signatures and as such is not affected by this vulnerability. The Biscuit implementations in Rust, Haskell, Go, Java and Javascript all have published versions following the v2 specification.

### Workarounds

There is no known workaround, any use of Biscuit v1 should be migrated to v2.

### References [Cryptanalysis of Aggregate Γ-Signature and Practical Countermeasures in Application to Bitcoin](https://eprint.iacr.org/2020/1484)

### For more information If you have any questions or comments about this advisory: * Open an issue in [biscuit-auth/biscuit](https://github.com/biscuit-auth/biscuit) * Ask questions on [Matrix](https://matrix.to/#/#biscuit-auth:matrix.org)

gsd-2022-31053

HSEC-2023-0002 — Improper Verification of Cryptographic Signature

Affected: Hackage: biscuit-haskell

# Improper Verification of Cryptographic Signature

The Biscuit specification version 1 contains a vulnerable algorithm that allows malicious actors to forge valid Γ-signatures. Such an attack would allow an attacker to create a token with any access level. The version 2 of the specification mandates a different algorithm than gamma signatures and as such is not affected by this vulnerability.