ZEBRA is a Zcash node written entirely in Rust. Prior to zebrad version 4.3.1 and prior to zebra-script version 5.0.2, after a refactoring, Zebra failed to validate a consensus rule that restricted the possible values of sighash hash types for V5 transactions which were enabled in the NU5 network upgrade. Zebra nodes could thus accept and eventually mine a block that would be considered invalid by zcashd nodes, creating a consensus split between Zebra and zcashd nodes. In a similar vein, for V4 transactions, Zebra mistakenly used the "canonical" hash type when computing the sighash while zcashd (correctly per the spec) uses the raw value, which could also crate a consensus split. This issue has been patched in zebrad version 4.3.1 and zebra-script version 5.0.2.
Following the refactoring, Zebra nodes stopped verifying the consensus rule limiting acceptable sighash type values for V5 transactions (introduced as part of the NU5 network upgrade). As a result, Zebra nodes could accept and eventually mine blocks considered invalid by zcashd nodes. Additionally, for V4 transactions, Zebra incorrectly applied the 'canonical' form of hash type when calculating sighash, while zcashd — according to the specification — uses the raw value. Both errors can lead to consensus split between implementations.
An attacker or malicious node can cause permanent consensus breakage in the Zcash network between Zebra nodes and zcashd, threatening the integrity and availability of the blockchain network and enabling acceptance or mining of blocks considered invalid by part of the network.
Update zebrad to version 4.3.1 or newer and zebra-script to version 5.0.2 or newer. Patches are available in the ZcashFoundation/zebra repository.
Zfnd zebrad in versions earlier than 4.3.1 and Zfnd zebra-script in versions earlier than 5.0.2
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:XZfnd Zebrad
APPZfnd< 4.3.1Zfnd Zebra Script
APPZfnd< 5.0.2
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