Snapshot signature not including HeadID will allow replay attacks

Vulnerability Description

Hydra is the layer-two scalability solution for Cardano. Prior to version 0.13.0, not signing and verifying `$\mathsf{cid}$` allows an attacker (which must be a participant of this head) to use a snapshot from an old head instance with the same participants to close the head or contest the state with it. This can lead to an incorrect distribution of value (= value extraction attack; hard, but possible) or prevent the head to finalize because the value available is not consistent with the closed utxo state (= denial of service; easy). A patch is planned for version 0.13.0. As a workaround, rotate keys between heads so not to re-use keys and not result in the same multi-signature participants.

References

• https://github.com/input-output-hk/hydra/security/advisories/GHSA-gr36-mc6v-72qq
• https://github.com/input-output-hk/hydra/blob/ec6c7a2ab651462228475d0b34264e9a182c22bb/hydra-node/src/Hydra/HeadLogic.hs#L357
• https://github.com/input-output-hk/hydra/blob/ec6c7a2ab651462228475d0b34264e9a182c22bb/hydra-node/src/Hydra/Snapshot.hs#L50-L54
• https://github.com/input-output-hk/hydra/blob/ec6c7a2ab651462228475d0b34264e9a182c22bb/hydra-plutus/src/Hydra/Contract/Head.hs#L583-L599