Impact
The staking contract accepts UpdateValidator transactions that set new_voting_key=Some(...) while omitting new_proof_of_knowledge. this skips the proof-of-knowledge requirement that is needed to prevent BLS rogue-key attacks when public keys are aggregated.
Because tendermint macro block justification verification aggregates validator voting keys and verifies a single aggregated BLS signature against that aggregate public key, a rogue-key voting key in the validator set can allow an attacker to forge a quorum-looking justification while only producing a single signature.
While the impact is critical, the exploitability is low: The voting keys are fixed for the epoch, so the attacker would need to know the next epoch validator set (chosen through VRF), which is unlikely.
Patches
The patch for this vulnerability is formally released as part of v1.3.0.
Workarounds
No known workarounds.
References
See PR.
Impact
The staking contract accepts
UpdateValidatortransactions that setnew_voting_key=Some(...)while omittingnew_proof_of_knowledge. this skips the proof-of-knowledge requirement that is needed to prevent BLS rogue-key attacks when public keys are aggregated.Because tendermint macro block justification verification aggregates validator voting keys and verifies a single aggregated BLS signature against that aggregate public key, a rogue-key voting key in the validator set can allow an attacker to forge a quorum-looking justification while only producing a single signature.
While the impact is critical, the exploitability is low: The voting keys are fixed for the epoch, so the attacker would need to know the next epoch validator set (chosen through VRF), which is unlikely.
Patches
The patch for this vulnerability is formally released as part of v1.3.0.
Workarounds
No known workarounds.
References
See PR.