---
title: "CVE-2026-52735: zebrad has consensus divergence via P2SH sigop undercount in pure-Rust disabled-opcode parser"
url: https://erroneo.us/security/cve/CVE-2026-52735/
description: "CVE-2026-52735 (zebra-script (crates.io (Rust))): ZEBRA is a Zcash node written entirely in Rust. Prior to 4.5.0, Zebra can accept a block that zcashd…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-08-18
date_modified: 2026-09-30
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-52735"
kev: false
cvss: 9.3
epss: 0.00507
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-52735: zebrad has consensus divergence via P2SH sigop undercount in pure-Rust disabled-opcode parser

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.5% , percentile 42: FIRST’s model estimates a 0.5% chance of exploitation activity in the next 30 days, higher than 42% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes zebra-script (crates.io (Rust)) <= 6.0.1, fixed in 7.0.0 ; zebrad (crates.io (Rust)) <= 4.4.1, fixed in 4.5.0 . Check your lockfile, including transitive dependencies.

## What it 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, p2shinputsigopcount used the pure-Rust script::Code::sigopcount path, whose tryfold parser stops at disabled opcodes such as OPCODESEPARATOR 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 MAXBLOCKSIGOPS 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.

## Affected packages

- crates.io (Rust) `zebra-script` <= 6.0.1 → fixed: 7.0.0
- crates.io (Rust) `zebrad` <= 4.4.1 → fixed: 4.5.0

## Affected products (CVE record)

- ZcashFoundation zebra: < 4.5.0

## Severity

- GitHub_M CVSS 4.0: 9.3 `CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:H`
- GitHub CVSS 4.0: 9.3 `CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:H`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable yes , technical impact partial .
- FIRST EPSS (model of 2026-10-21): 0.51% probability of exploitation activity in the next 30 days; percentile 42.

## Sources

- [GitHub Advisory GHSA-gf9r-m956-97qx](https://github.com/advisories/GHSA-gf9r-m956-97qx)
- [CVE.org record CVE-2026-52735](https://www.cve.org/CVERecord?id=CVE-2026-52735)
- [NVD entry CVE-2026-52735](https://nvd.nist.gov/vuln/detail/CVE-2026-52735)
- [github.com](https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-gf9r-m956-97qx)
- [github.com](https://github.com/ZcashFoundation/zebra/commit/1440b43ca7df59aca948090d45117557b217a6cd)
- [github.com](https://github.com/ZcashFoundation/zebra/releases/tag/v4.5.0)
- [github.com](https://github.com/AlfredoG87/zcash_script/blob/v0.4.4/src/script/iter.rs#L104-L115)
- [github.com](https://github.com/ZcashFoundation/zebra/blob/d4cd662c716382f6397d2a730148025a1ca79fec/zebra-consensus/src/block.rs#L140)
- [github.com](https://github.com/ZcashFoundation/zebra/blob/d4cd662c716382f6397d2a730148025a1ca79fec/zebra-script/src/lib.rs#L383-L400)

---
Source page: https://erroneo.us/security/cve/CVE-2026-52735/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt