---
title: "CVE-2026-54496: Zebra: Missing copy constraint in halo2_gadgets variable-base scalar multiplication allows under-constrained base, breaking Orchard Action circuit soundness"
url: https://erroneo.us/security/cve/CVE-2026-54496/
description: "CVE-2026-54496 (zebrad (crates.io (Rust))): ZEBRA is a Zcash node written entirely in Rust. Prior to zebrad 5.0.0, halo2gadgets 0.5.0, orchard 0.14.0…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-07-17
date_modified: 2026-07-17
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-54496"
kev: false
cvss: 9.3
epss: 0.00315
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-54496: Zebra: Missing copy constraint in halo2_gadgets variable-base scalar multiplication allows under-constrained base, breaking Orchard Action circuit soundness

**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 0.3% , percentile 23: FIRST’s model estimates a 0.3% chance of exploitation activity in the next 30 days, higher than 23% 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 zebrad (crates.io (Rust)) <= 4.5.1, fixed in 5.0.0 ; halo2_gadgets (crates.io (Rust)) < 0.5.0, fixed in 0.5.0 ; orchard (crates.io (Rust)) < 0.14.0, fixed in 0.14.0 ; zcash_primitives (crates.io (Rust)) < 0.28.0, fixed in 0.28.0 . Check your lockfile, including transitive dependencies.

## What it is

ZEBRA is a Zcash node written entirely in Rust. Prior to zebrad 5.0.0, halo2gadgets 0.5.0, orchard 0.14.0, zcashprimitives 0.28.0, and zcashd 6.20.0, the variable-base scalar multiplication gadget in halo2gadgets/src/ecc/chip/mul/incomplete.rs used assignadvice() for the base point without a copy constraint tying it to the actual base, allowing a malicious prover to produce a valid proof for an Orchard Action with an under-constrained base point and bypass the diversified-address-integrity check that binds pkd, gd, ivk, the nullifier (nf), and the spend validating key (ak) to the note being spent. This issue is fixed in zebrad 5.0.0, halo2gadgets 0.5.0, orchard 0.14.0, zcashprimitives 0.28.0, and zcashd 6.20.0.

## Affected packages

- crates.io (Rust) `zebrad` <= 4.5.1 → fixed: 5.0.0
- crates.io (Rust) `halo2_gadgets` < 0.5.0 → fixed: 0.5.0
- crates.io (Rust) `orchard` < 0.14.0 → fixed: 0.14.0
- crates.io (Rust) `zcash_primitives` < 0.28.0 → fixed: 0.28.0

## Affected products (CVE record)

- ZcashFoundation zebra: < 5.0.0
- zcash halo2_gadgets: < 0.5.0
- zcash orchard: < 0.14.0
- zcash librustzcash: < 0.28.0
- zcash zcash: < 6.20.0

## Severity

- GitHub_M CVSS 3.1: 9.3 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:L`
- GitHub CVSS 3.1: 9.3 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:L`

## 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): 0.32% probability of exploitation activity in the next 30 days; percentile 23.

## Sources

- [GitHub Advisory GHSA-ww9q-8r59-xv46](https://github.com/advisories/GHSA-ww9q-8r59-xv46)
- [CVE.org record CVE-2026-54496](https://www.cve.org/CVERecord?id=CVE-2026-54496)
- [NVD entry CVE-2026-54496](https://nvd.nist.gov/vuln/detail/CVE-2026-54496)
- [github.com](https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-ww9q-8r59-xv46)
- [github.com](https://github.com/ZcashFoundation/zebra/releases/tag/v5.0.0)
- [github.com](https://github.com/zcash/halo2/releases/tag/halo2_gadgets-0.5.0)
- [github.com](https://github.com/zcash/librustzcash/releases/tag/zcash_primitives-0.28.0)
- [github.com](https://github.com/zcash/orchard/releases/tag/0.14.0)
- [github.com](https://github.com/zcash/zcash/releases/tag/v6.20.0)
- [zfnd.org](https://zfnd.org/zebra-4-5-3-and-5-0-0-emergency-soft-fork-and-nu6-2-activation)

---
Source page: https://erroneo.us/security/cve/CVE-2026-54496/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt