Executive brief
Zebra, a software implementation of the Zcash cryptocurrency node, contains a flaw in how it validates transaction signatures. This vulnerability allows a malicious actor to submit specially crafted transactions that Zebra nodes accept but other Zcash nodes (like zcashd) reject. This can lead to a 'consensus split,' effectively splitting the network into two different versions of history, which could disrupt services and potentially allow for double-spend attacks.
Technical details
A refactoring of the Zebra transaction verification logic moved consensus-critical checks from C++ to Rust but failed to re-implement a rule restricting sighash hash types for V5 transactions. Additionally, Zebra incorrectly used canonical hash types for V4 transactions instead of raw values as required by the Zcash specification. An attacker can exploit these discrepancies by submitting transactions with invalid hash types, causing Zebra nodes to accept blocks that the rest of the network (running zcashd) considers invalid. This results in a consensus split and network partitioning. The issue is fixed in zebrad 4.3.1 and zebra-script 5.0.2.
Affected products
- Zcash Foundation zebrad < 4.3.1
- Zcash Foundation zebra-script < 5.0.2
Timeline
- 2026-04-18: advisory: GitHub Advisory published
- 2026-04-18: patched: Fix released in version 4.3.1