CVE-2026-44497: Zfnd Zebra-script Consensus Vulnerability

CVE-2026-44497 Overview

CVE-2026-44497 affects Zebra, a Zcash node implementation written in Rust maintained by the Zcash Foundation. The vulnerability stems from insufficient error handling during sighash computation when the sighash type is invalid. Instead of returning an error, execution continues and leaves the input sighash buffer untouched. A prior valid signature validation can leave a valid sighash in the buffer, allowing an invalid hash-type to be incorrectly accepted. The flaw can cause a consensus split between Zebra and zcashd nodes. The issue was introduced by the fix for CVE-2026-41583 and has been patched in zebrad 4.4.0 and zebra-script 6.0.0.

Critical Impact
An attacker can trigger acceptance of transactions with invalid sighash types on Zebra nodes, producing a network consensus split with zcashd nodes and threatening blockchain integrity.

Affected Products

zfnd zebrad prior to version 4.4.0
zfnd zebra-script prior to version 6.0.0
Zcash network participants running vulnerable Zebra builds

Discovery Timeline

2026-05-08 - CVE-2026-44497 published to NVD
2026-05-08 - Last updated in NVD database

Technical Details for CVE-2026-44497

Vulnerability Analysis

The vulnerability is an improper signature validation issue classified as [CWE-347]. Zebra's sighash computation routine fails to propagate an error when the sighash type provided in a transaction input is invalid. Normal execution continues without overwriting or clearing the sighash buffer used for verification.

When a prior input in the same transaction successfully computes a valid sighash, that sighash remains in the buffer. The subsequent input with an invalid hash-type then reuses the leftover buffer contents during signature verification. The verification can succeed against the stale sighash, causing Zebra to accept a transaction that zcashd rejects.

This divergence in validation behavior produces a consensus split. Nodes running Zebra build a chain state that differs from nodes running zcashd, undermining the single-chain guarantee that proof-of-work consensus depends on.

Root Cause

The root cause is insufficient error handling in the sighash computation path introduced by the earlier patch for CVE-2026-41583. The invalid-sighash-type code path returns to normal flow rather than producing an error, leaving caller state inconsistent with caller expectations.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker crafts a Zcash transaction with multiple inputs where one or more inputs specify an invalid sighash type. The attacker broadcasts the transaction or includes it in a mined block to expose Zebra nodes to the divergent validation outcome.

The vulnerability mechanism is described in the Zcash Foundation GitHub Security Advisory. No public proof-of-concept exploit is available at the time of publication.

Detection Methods for CVE-2026-44497

Indicators of Compromise

Zebra nodes reporting a chain tip or best block hash that differs from peers running zcashd at the same height
Unexpected chain reorganizations or persistent forks observed on Zebra nodes
Acceptance of transactions or blocks by Zebra that are rejected by reference zcashd peers

Detection Strategies

Compare getbestblockhash and getblockhash RPC responses between local Zebra nodes and trusted zcashd nodes at matching heights
Inspect the version banner reported by Zebra nodes and flag any instance running zebrad below 4.4.0 or linked against zebra-script below 6.0.0
Audit mempool and accepted block contents for transaction inputs that carry non-standard or undefined sighash type bytes

Monitoring Recommendations

Add alerts for divergence between Zebra and zcashd node states, including block hash, transaction acceptance, and chain height
Monitor consensus-layer logs for signature validation anomalies and sighash type parsing events
Track upstream advisories from the Zcash Foundation repository for follow-on issues affecting the script verification stack

How to Mitigate CVE-2026-44497

Immediate Actions Required

Upgrade all Zebra deployments to zebrad 4.4.0 or later and zebra-script 6.0.0 or later
Inventory all running Zebra instances, including validator, indexing, and wallet backends, and confirm patched versions are loaded
Re-synchronize any Zebra node that may have followed a divergent chain prior to patching

Patch Information

The Zcash Foundation released fixed versions zebrad 4.4.0 and zebra-script 6.0.0. The patch ensures that an invalid sighash type returns an explicit error rather than allowing execution to fall through with a stale buffer. Patch details and release artifacts are available in the Zcash Foundation Security Advisory GHSA-gq4h-3grw-2rhv.

Workarounds

No vendor-supplied workaround exists; upgrading to the fixed versions is the only supported remediation
Operators who cannot upgrade immediately should cross-validate critical transactions against a zcashd reference node before acting on Zebra-only confirmations
Restrict downstream services from relying solely on a single Zebra node for finality decisions until the patch is applied

bash

# Verify installed versions and upgrade via cargo
zebrad --version
cargo install --locked --version 4.4.0 zebrad
cargo update -p zebra-script --precise 6.0.0