CVE-2026-44497 (GCVE-0-2026-44497)

Vulnerability from cvelistv5 – Published: 2026-05-08 15:08 – Updated: 2026-05-08 15:48

Title

ZEBRA: Consensus Divergence in Transparent Sighash Hash-Type Handling due to Stale Buffer

Summary

ZEBRA is a Zcash node written entirely in Rust. Prior to zebrad version 4.4.0 and prior to zebra-script version 6.0.0, the fix for CVE-2026-41583 introduced a separate issue due to insufficient 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. This issue has been patched in zebrad version 4.4.0 and zebra-script version 6.0.0.

Severity ?

9.3 (Critical)


                        
                          CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:H/SA:H

CWE

CWE-347 - Improper Verification of Cryptographic Signature

Assigner

GitHub_M

References

URL

Tags

https://github.com/ZcashFoundation/zebra/security…

x_refsource_CONFIRM

Impacted products

	Vendor	Product	Version
	ZcashFoundation	zebra	Affected: zebra-script < 6.0.0 Affected: zebrad < 4.4.0

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-44497

Vulnerability from fkie_nvd - Published: 2026-05-08 15:17 - Updated: 2026-05-08 18:42

Severity ?

9.1 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-gq4h-3grw-2rhv	Vendor Advisory

Impacted products

	Vendor	Product	Version
	zfnd	zebra-script	*
	zfnd	zebrad	*

JSON

To clipboard

{
  "configurations": [
    {
      "nodes": [
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          "cpeMatch": [
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    }
  ],
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  "lastModified": "2026-05-08T18:42:24.100",
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GHSA-GQ4H-3GRW-2RHV

Vulnerability from github – Published: 2026-05-07 20:56 – Updated: 2026-05-07 20:56

Summary

Zebra has Consensus Divergence in Transparent Sighash Hash-Type Handling due to Stale Buffer

Details

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_CHECKSIGVERIFY immediately before an OP_CHECKSIG with an undefined hash type.
The first opcode primes the C++ sighash buffer with a valid digest; the second causes Zebra's callback to return None while 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.

Severity ?

9.3 (Critical)


                  
                    CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:H/SA:H

Show details on source website

JSON

To clipboard

{
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    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 5.0.1"
      },
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        "ecosystem": "crates.io",
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        }
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    }
  ],
  "aliases": [
    "CVE-2026-44497"
  ],
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    "cwe_ids": [
      "CWE-347"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-07T20:56:21Z",
    "nvd_published_at": null,
    "severity": "CRITICAL"
  },
  "details": "# CVE-2026-44497: Consensus Divergence in Transparent Sighash Hash-Type Handling due to Stale Buffer\n\n## Summary\n\nThe 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.\n\n## Severity\n\n**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.\n\nNote that the impact is currently alleviated by the fact that currently most miners run `zcashd`.\n\n## Affected Versions\n\nZebra 4.3.1.\n\n## Description\n\nVerification 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.\n\nAn attacker could exploit this by:\n\n- Constructing a transparent output spent by a script that runs a valid `OP_CHECKSIGVERIFY` immediately before an `OP_CHECKSIG` with an undefined hash type.\n- The first opcode primes the C++ sighash buffer with a valid digest; the second causes Zebra\u0027s callback to return `None` while the C++ checker verifies the invalid signature against the stale digest.\n- Zebra accepts the spend, zcashd rejects it, creating a consensus split in the network.\n\n## Impact\n\n**Consensus Failure**\n\n- **Attack Vector:** Network.\n- **Effect:** Network partition/consensus split.\n- **Scope:** Any affected Zebra node, and any miner or template pipeline that relies on Zebra\u0027s validation result.\n\n## Fixed Versions\n\nThis issue is fixed in 4.4.0.\n\nThe 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.\n\n## Mitigation\n\nUsers should upgrade to 4.4.0 or later immediately.\n\nThere 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.\n\n## Credits\n\nZebra thanks @sangsoo-osec for finding and reporting the issue.",
  "id": "GHSA-gq4h-3grw-2rhv",
  "modified": "2026-05-07T20:56:21Z",
  "published": "2026-05-07T20:56:21Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-gq4h-3grw-2rhv"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/ZcashFoundation/zebra"
    },
    {
      "type": "WEB",
      "url": "https://github.com/ZcashFoundation/zebra/releases/tag/v4.4.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:H/SA:H",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Zebra has Consensus Divergence in Transparent Sighash Hash-Type Handling due to Stale Buffer"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

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CVE-2026-44497 (GCVE-0-2026-44497)

FKIE_CVE-2026-44497

GHSA-GQ4H-3GRW-2RHV

CVE-2026-44497: Consensus Divergence in Transparent Sighash Hash-Type Handling due to Stale Buffer

Summary

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Affected Versions

Description

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Fixed Versions

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