CVE-2026-44497 — zebra-script
CVE-2026-44497 is a CWE-347 vulnerability in zebra-script. A fix is available for zebra-script — see the affected versions and patch details below.
ZEBRA: Consensus Divergence in Transparent Sighash Hash-Type Handling due to Stale Buffer
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.
- 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 CVE-2026-44497.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
zebra-script🦀zebradReal-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-2026-44497: Consensus Divergence in Transparent Sighash Hash-Type Handling due to Stale Buffer
Summary
The fix for https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-8m29-fpq5-89jj introduced a separate issue due to insuficient error handling of the case where the sighash type is invalid, during sighash computation. Instead of returning an error, the normal flow would resume, and the input sighash buffer would be left untouched. In scenarios where a previous signature validation could leave a valid sighash in the buffer, an invalid hash-type could be incorrectly accepted, which would create a consensus split between Zebra and zcashd nodes.
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 4.3.1.
Description
Verification of transparent transactions inherits the Bitcoin Script verification code in C++, called from Zebra through a foreign function interface (FFI) with a Rust callback that computes the sighash. The fix for https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-8m29-fpq5-89jj added the missing V5 hash-type consensus check on the Rust side, returning None for undefined hash types. However, the FFI bridge only writes to the C++ sighash buffer when the callback returns Some, and the C++ checker reads that buffer unconditionally, so the failure signal is lost.
An attacker could exploit this by:
- Constructing a transparent output spent by a script that runs a valid
OP_CHECKSIGVERIFYimmediately before anOP_CHECKSIGwith an undefined hash type. - The first opcode primes the C++ sighash buffer with a valid digest; the second causes Zebra's callback to return
Nonewhile the C++ checker verifies the invalid signature against the stale digest. - Zebra accepts the spend, zcashd rejects it, creating a consensus split in the network.
Impact
Consensus Failure
- Attack Vector: Network.
- Effect: Network partition/consensus split.
- Scope: Any affected Zebra node, and any miner or template pipeline that relies on Zebra's validation result.
Fixed Versions
This issue is fixed in 4.4.0.
The fixes uses a workaround where the input buffer is filled with random bytes on validation failure, which makes signature validation fail (as expected) with overwhelming probability. This avoids a breaking release of the zcash_script crate. A future release will propagate the error correctly for a direct fix.
Mitigation
Users should upgrade to 4.4.0 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 for finding and reporting the issue.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | zebra-script | all versions | 6.0.0cargo update -p zebra-script --precise 6.0.0 |
| 🦀crates.io | zebrad | all versions | 4.4.0cargo update -p zebrad --precise 4.4.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for zebra-script, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update zebra-script to 6.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-44497 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.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-44497 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-44497. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-44497 in your dependencies?
O3 Security finds CVE-2026-44497 across crates.io dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.