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CVSS estimates technical severity, but it does not automatically equal business risk. Prioritize using context like internet exposure, asset criticality, known exploitation, and whether compensating controls exist. A Medium CVSS on an exposed production system can be more urgent than a Critical on an isolated non-production host.

Vulnerability Database

Q: What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

Q: What's the difference between a vulnerability, an exploit, and a zero-day?

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. Risk increases sharply when exploitation becomes reliable or widespread.

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Recurring findings usually come from incomplete asset discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host.

Q: How do we prioritize remediation without burning out the team?

Use a repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress so remediation is steady, not reactive.

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352,427

Total vulnerabilities in the database

Zebra v4.4.0 still accepts V5 SIGHASH_SINGLE without a corresponding output — zebrad

Improper Validation of Integrity Check Value

Consensus Divergence in V5 Transparent SIGHASH_SINGLE With No Corresponding Output

Summary

Zebra failed to enforce a ZIP-244 consensus rule for V5 transparent transactions: when an input is signed with SIGHASH_SINGLE and there is no transparent output at the same index as that input, validation must fail. Zebra instead asked the underlying sighash library to compute a digest, and that library produced a digest over an empty output set rather than failing. An attacker could craft a V5 transaction with more transparent inputs than outputs that Zebra accepts but zcashd rejects, creating a consensus split between Zebra and zcashd nodes.

A previous fix (GHSA-cwfq-rfcr-8hmp) addressed a closely related case in the same area of the code, but did not cover this specific one.

Severity

Critical - This is a Consensus Vulnerability that could allow a malicious party to induce network partitioning, service disruption, and potential double-spend attacks against affected nodes.

Note that the impact is currently alleviated by the fact that currently most miners run zcashd.

Affected Versions

Zebra 4.4.0.

Description

Verification of transparent transactions inherits the Bitcoin Script verification code in C++. Since it is consensus-critical, this code is called from Zebra through a foreign function interface (FFI), with a Rust callback that computes the sighash for each input being verified.

ZIP-244 §S.2a marks two situations as consensus failure for V5 transparent signatures:

The signed hash type is not one of the six canonical values; and
The hash type is SIGHASH_SINGLE (alone or combined with ANYONECANPAY) and the input has no transparent output at the same index.

zcashd enforces both rules: its SignatureHash raises an exception, and CheckSig catches it and fails the script. A previous fix (GHSA-cwfq-rfcr-8hmp) added the first rule to Zebra's V5 sighash callback. The second rule, however, was not added — Zebra's callback forwarded the request to librustzcash's ZIP-244 implementation, which handles an out-of-range SIGHASH_SINGLE output index by hashing an empty output set rather than refusing to produce a digest. As a result, Zebra would compute a well-defined sighash for the missing-output case and accept any signature that verified against it.

An attacker could exploit this by:

Constructing a V5 transaction with two or more transparent inputs and fewer transparent outputs;
Signing an input whose index has no matching vout entry with SIGHASH_SINGLE (0x03) or SIGHASH_SINGLE|ANYONECANPAY (0x83), using the digest Zebra computes;
Broadcasting the transaction, or a block containing it, to the network.

Zebra would verify the transaction's transparent script and accept the transaction (and any block containing it), while zcashd would reject both, splitting Zebra nodes from the rest of the network.

Impact

Consensus Failure

Attack Vector: Network.
Effect: Network partition/consensus split.
Scope: Any affected Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.4.1.

Mitigation

Users should upgrade to Zebra 4.4.1 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to ensure the node remains on the correct consensus path and is protected against malicious chain forks.

Credits

Zebra thanks @sangsoo-osec, @zmanian, and @fivelittleducks for finding and reporting the issue.

Published: May 8, 2026
Updated: Jun 5, 2026
GHSA: GHSA-pvmv-cwg8-v6c8
Severity: Critical
Exploit:
CISA KEV:

No technical information available.

CWEs:

Affected Software
References

Software	From	Fixed in
zebrad	-	4.4.1
zebra-script	-	6.0.1

https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-pvmv-cwg8-v6c8

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Frequently Asked Questions

What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.