ZcashFoundation Zebra up to 4.4.x P2SH Signature Operation Counter zebra-script/src/lib.rs p2sh_input_sigop_count input validation

Summaryinfo

A vulnerability was found in ZcashFoundation Zebra up to 4.4.x. It has been classified as critical. Impacted is the function p2sh_input_sigop_count of the file zebra-script/src/lib.rs of the component P2SH Signature Operation Counter. Performing a manipulation results in input validation. This vulnerability is known as CVE-2026-52735. Remote exploitation of the attack is possible. No exploit is available.

Detailsinfo

A vulnerability, which was classified as critical, was found in ZcashFoundation Zebra up to 4.4.x. This affects the function p2sh_input_sigop_count of the file zebra-script/src/lib.rs of the component P2SH Signature Operation Counter. The manipulation with an unknown input leads to a input validation vulnerability. CWE is classifying the issue as CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. This is going to have an impact on integrity, and availability. The summary by CVE is:

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.

It is possible to read the advisory at github.com. This vulnerability is uniquely identified as CVE-2026-52735 since 06/08/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 4.5.0 eliminates this vulnerability.

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Productinfo

Vendor

• ZcashFoundation

Name

• Zebra

Version

• 4.0
• 4.1
• 4.2
• 4.3
• 4.4

Website

• Product: https://github.com/ZcashFoundation/zebra/

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