Zebra Vulnerable to Consensus Divergence in Transparent Sighash Hash-Type HandlingGHSA-8m29-fpq5-89jj
CRITICALFix: ZcashFoundation/zebra@1f605ecGHSA-8m29-fpq5-89jj is a critical-severity (CVSS 9.1) CWE-573 vulnerability in zebrad. A fix is available for zebrad — see the affected versions and patch details below.
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-8m29-fpq5-89jj.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
zebrad🦀zebra-scriptReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.
Description
CVE-2026-41583: Consensus Divergence in Transparent Sighash Hash-Type Handling
Summary
After a refactoring, Zebra failed to validate a consensus rule that restricted the possible values of sighash hash types for V5 transactions which were enabled in the NU5 network upgrade. Zebra nodes could thus accept and eventually mine a block that would be considered invalid by zcashd nodes, creating a consensus split between Zebra and zcashd nodes.
In a similar vein, for V4 transactions, Zebra mistakenly used the "canonical" hash type when computing the sighash while zcashd (correctly per the spec) uses the raw value, which could also crate a consensus split.
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
All Zebra versions prior to version 4.3.1. (Some older versions are not impacted but are no longer supported by the network.)
Description
Verification of transparent transactions inherits the Bitcoin Script verification code in C++. Since it is consensus-critical, this code was called from Zebra through foreign function interface (FFI). That interface was clunky because it required parsing the whole transaction in C++ code, which would then pull Rust libraries which could get in conflict with Zebra code. A refactoring was done so that only the verification itself was done in C++, and the rest done by Rust code, using a callback. However, in this refactoring, it was not noticed that a particular consensus rule - only accepting known hash types in transparent transaction signatures - was being enforced in C++ code and thus had to be enforced by the Rust caller.
An attacker could exploit this by:
- Submitting a V4 or V5 transaction with an invalid hash type
- The V5 transaction would be accepted by Zebra nodes but not by
zcashdnodes (and vice-versa for V4), creating a consensus split in the network.
Impact
Consensus Failure
- Attack Vector: Network.
- Effect: Network partition/consensus split.
- Scope: Any Zebra affected Zebra node
Fixed Versions
This issue is fixed in Zebra 4.3.1.
The fix adds the consensus check in the caller of the C++ verification code. It also uses the raw hash type for V4 sighash computations.
Mitigation
Users should upgrade to Zebra 4.3.1 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
Thanks Alex “Scalar” Sol for finding and reporting the issue, and to @sangsoo-osec who independently found the same issue and demonstrated that the V4 variant was also exploitable.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | zebrad | all versions | 4.3.1cargo update -p zebrad --precise 4.3.1 |
| 🦀crates.io | zebra-script | all versions | 5.0.2cargo update -p zebra-script --precise 5.0.2 |
Affected Products
zebra-scriptzfndzebradzfndDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for zebrad, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update zebrad to 4.3.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-8m29-fpq5-89jj is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is GHSA-8m29-fpq5-89jj in your dependencies?
Find it across crates.io, including transitive dependencies.