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

> Unauthenticated attackers can crash the Zebra node by sending a malformed transaction, causing a denial of service.

- **Severity:** High 8.7 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 12 Oct 2026
- **Updated:** 13 Oct 2026
- **Also known as:** GHSA-47j7-v7c6-f9jg, GHSA-h5rr-8pqv-grp9

## What is CVE-2026-109363?

CVE-2026-109363 is a high-severity denial of service vulnerability in ZcashFoundation zebra, published on 12 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-617 (Reachable Assertion)

## Which versions are affected by CVE-2026-109363?


## How do I fix CVE-2026-109363?

No fix has been published for CVE-2026-109363 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-109363 being exploited?

There is no known exploitation of CVE-2026-109363 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-109363 and fix it if it is affected.

What it is: CVE-2026-109363 is a high-severity denial of service vulnerability in ZcashFoundation zebra, published on 12 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-109363 in the wild and no public exploit code.

Affected product: ZcashFoundation zebra. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-109363/ (Markdown: https://insights.sbomify.com/CVE-2026-109363/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-109363
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-109363
- OSV: https://osv.dev/vulnerability/CVE-2026-109363

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-109363/
Summaries are generated and may contain mistakes; the official description above is the record.