CVE-2026-52735
CriticalCVSS 9.3Summary
ZEBRA, a Zcash node written in Rust, before version 4.5.0 can accept a block that zcashd rejects due to undercounting the P2SH signature-operation counter for scripts containing a disabled opcode. An attacker can exploit this to cause a chain split, affecting network integrity and availability.
Risk Assessment
A chain split can lead to double spending, loss of network trust, and operational disruptions, potentially causing significant financial consequences for users.
Recommendation
Update ZEBRA to version 4.5.0 or later, which includes the fix. Monitor the network for unusual blocks.
Original NVD description (English source)
ZEBRA is a Zcash node written entirely in Rust. Prior to 4.5.0, Zebra can accept a block that zcashd rejects because the P2SH signature-operation counter undercounts redeem scripts containing a disabled opcode followed by signature opcodes. In zebra-script/src/lib.rs, p2sh_input_sigop_count used the pure-Rust script::Code::sig_op_count path, whose try_fold parser stops at disabled opcodes such as OP_CODESEPARATOR and returns only the partial count accumulated before the error. The zcashd reference implementation continues static signature-operation counting through disabled opcodes, so an attacker can broadcast P2SH spends that Zebra counts below MAX_BLOCK_SIGOPS while zcashd counts above the 20,000-operation limit. If a Zebra miner includes those transactions, Zebra validators accept the block while zcashd validators reject it, creating a consensus chain split that affects network integrity and availability without requiring the attacker to produce a block. This issue is fixed in version 4.5.0.