# CVE-2026-52735: ZEBRA: Consensus divergence via P2SH sigop undercount in pure-Rust disabled-opcode parser

> An attacker can cause a consensus chain split in Zebra nodes by exploiting a signature operation counting error, leading to network availability issues.

- **Severity:** Critical 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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 Aug 2026
- **Updated:** 18 Aug 2026
- **Also known as:** GHSA-gf9r-m956-97qx

## What is CVE-2026-52735?

CVE-2026-52735 is a critical denial of service vulnerability in ZcashFoundation zebra, published on 18 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-684 (Incorrect Provision of Specified Functionality)

## Which versions are affected by CVE-2026-52735?

4 open source packages ship an affected version, including zebra-script and zebrad.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `zebra-script` | crates.io | All versions | 7.0.0 |
| `zebra-script` | crates.io | All versions | 7.0.0 |
| `zebrad` | crates.io | All versions | 4.5.0 |
| `zebrad` | crates.io | All versions | 4.5.0 |

## How do I fix CVE-2026-52735?

Upgrade zebra-script to 7.0.0 or later.

## Is CVE-2026-52735 being exploited?

There is no known exploitation of CVE-2026-52735 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-52735 and fix it if it is affected.

What it is: CVE-2026-52735 is a critical denial of service vulnerability in ZcashFoundation zebra, published on 18 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-52735 in the wild and no public exploit code.

Affected packages and fixed versions:
- zebra-script (crates.io): affected all versions; fixed in 7.0.0
- zebra-script (crates.io): affected all versions; fixed in 7.0.0
- zebrad (crates.io): affected all versions; fixed in 4.5.0
- zebrad (crates.io): affected all versions; fixed in 4.5.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-52735/ (Markdown: https://insights.sbomify.com/CVE-2026-52735/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-52735
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-52735
- OSV: https://osv.dev/vulnerability/CVE-2026-52735

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-52735/
Summaries are generated and may contain mistakes; the official description above is the record.