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

> Attackers can force Zebra nodes to drop valid blocks by forging coinbase heights, delaying tip discovery and causing denial of service for mining backends.

- **Severity:** Medium 6.3 (`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`)
- **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:** 26 Oct 2026
- **Also known as:** GHSA-4f6v-mj46-gxg3, GHSA-mprq-2cjh-7qc2

## What is CVE-2026-109366?

CVE-2026-109366 is a medium-severity 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

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.

Weakness: CWE-354 (Improper Validation of Integrity Check Value)

## Which versions are affected by CVE-2026-109366?


## How do I fix CVE-2026-109366?

No fix has been published for CVE-2026-109366 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-109366 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-109366 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-109366 and fix it if it is affected.

What it is: CVE-2026-109366 is a medium-severity 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: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-109366 exists.

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-2026-109366/ (Markdown: https://insights.sbomify.com/CVE-2026-109366/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-109366
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-109366
- OSV: https://osv.dev/vulnerability/CVE-2026-109366

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-109366/
Summaries are generated and may contain mistakes; the official description above is the record.