CVE-2026-104422
Received Received - Intake

Block Sync Height Validation Bypass in Zebra

Publication date: 2026-10-02

Last updated on: 2026-10-02

Assigner: VulnCheck

Description
The block sync download path in Zebra (zebrad) before 6.3.0 reads a block's height from its unvalidated coinbase scriptSig and drops blocks that appear too far behind the tip before consensus validation, without penalizing the supplying peer. Because V5 transaction IDs exclude the scriptSig, a malicious peer can repeatedly serve a canonical block whose coinbase claims height 1 while keeping the requested hash, delaying the node's discovery of the newest block.

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Meta Information

Published
2026-10-02
Last Modified
2026-10-02
Generated
2026-10-02
AI Q&A
2026-10-02
EPSS Evaluated
N/A
NVD
CVE-2026-104422
EUVD
EUVD-2026-91433

Affected Vendors & Products

Showing 3 associated CPEs
Vendor Product Version / Range
zebracore zebra 6.3.0
zebracore zebra to 6.3.0 (exc)
zebra zebrad to 6.3.0 (exc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-345 The product does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data.

Attack-Flow Graph

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Executive Summary

This is a Denial of Service (DoS) vulnerability in Zebra before version 6.3.0. It involves a malicious peer exploiting the block sync process by serving a canonical block with a forged coinbase scriptSig claiming an incorrect height (e.g., height 1). The node reads this unvalidated height, drops the block as outdated, and delays discovering the newest block. The attack works because transaction IDs exclude the scriptSig, allowing the block hash to remain unchanged.

Detection Guidance

Monitor Zebra logs for repeated block drops with incorrect heights or delays in block synchronization. Check for peers sending blocks with coinbase scriptSig claiming height 1 while maintaining valid hashes. Use network monitoring tools to detect unusual delays in block propagation from specific peers.

Impact Analysis

For mining operators, this can lead to wasted hash power on obsolete work due to delayed tip discovery. Nodes may experience prolonged synchronization delays, reducing network efficiency. The attack does not require privileges or user interaction and can be executed remotely by a malicious peer.

Compliance Impact

This vulnerability primarily impacts system availability by enabling a denial-of-service attack that delays block synchronization, which could disrupt operations but does not directly involve unauthorized data access or processing. Compliance with standards like GDPR or HIPAA typically focuses on data protection, access controls, and auditability, which are not directly affected by this issue.

Mitigation Strategies

Upgrade Zebra to version 6.3.0 or later immediately. Avoid peering with untrusted nodes until patched. For mining operators, monitor parent block ages closely to detect delays. Consider temporary use of trusted peers as a workaround until full patching.

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