ZEBRA Consensus Vulnerability Allowing Malicious Miners to Induce Network Splits

A logic error in ZEBRA's transaction verification cache prior to version 4.3.1 in the ZEBRA node and prior to version 5.0.2 in the zebra-consensus package could enable a malicious miner to create a consensus split. This was achieved by submitting a transaction valid for height H+1 but invalid for H+2, and then mining it into a block at H+2. Vulnerable ZEBRA nodes would accept the invalid block, causing a split from the Zcash network.

Impact

Exploitation of this vulnerability could lead to a consensus failure, causing a network partition where the affected ZEBRA node is isolated from the rest of the network.

Reproduction

To reproduce this vulnerability, a transaction must be submitted with an expiry height of H+1. After mining a block at H+1, the same transaction can be included in a block mined at H+2, which is then submitted before the H+1 block. Vulnerable ZEBRA nodes will accept the H+2 block, leading to a consensus split.

Remediation

Users should upgrade to ZEBRA version 4.3.1 or later. There are no known workarounds for this issue.