Zebra (zebrad): Denial of service in block sync via coinbase scriptSig rewrite
Summary
Zebra (zebrad), the Zcash node software, is affected in versions before 6.3.0. A malicious peer can answer a block download with a copied block whose coinbase scriptSig claims a far-behind height, and the node drops the block before consensus validation without penalizing the peer. This delays the node's discovery of the newest block, which is an availability impact only. Exploitation requires no authentication, only that the node syncs from the P2P network, which is the default.
Affected
- Zebra (zebrad) before 6.3.0 (the GitHub advisory lists versions up to and including 6.2.3)
Fixed in
- Zebra (zebrad) 6.3.0
Workaround
Unknown.
Exploitation
- CISA SSVC: exploitation none, automatable yes, technical impact partial
- No public proof of concept or in-the-wild exploitation found in the sources consulted
Our recommendation
- Check whether any zebrad node or Zebra crate is deployed in your environment.
- Upgrade affected nodes to Zebra 6.3.0 or later; the latest release is preferred.
- Monitor nodes for chain-tip lag as a sign of this issue.
- No action needed if Zebra is not deployed.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- GitHub Security Advisory GHSA-g95h-hw6g-pvgv github.com
- VulnCheck advisory for Zebra before 6.3.0 www.vulncheck.com
- OSV record CVE-2026-104422 osv.dev
- Vulners CVE-2026-104422 vulners.com
- Zebra releases github.com
- Zebra security advisories github.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 1 Nov 2026, 06:03.
Original description (NVD)
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.
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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