# CVE-2026-66364: MZ Automation libiec61850 Out-of-bounds Read

> An attacker can cause a denial of service in libiec61850 subscribers by sending a crafted multicast frame that triggers an out-of-bounds read.

- **Severity:** High 7.1 (`CVSS:4.0/AV:A/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:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 30 Jul 2026
- **Updated:** 31 Jul 2026
- **Also known as:** GHSA-hw99-2wcp-34xq

## What is CVE-2026-66364?

CVE-2026-66364 is a high-severity denial of service vulnerability in MZ Automation GmbH libiec61850, published on 30 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

The GOOSE payload parser contains a boundary handling flaw that can be 
triggered by a single unauthenticated Layer 2 multicast frame on the 
process bus. When processing specific payload fields, an attacker 
controlled inner element length may exceed its enclosing length, causing
 the parser to over read by one byte. This out-of-bounds read reliably 
terminates the subscriber process, resulting in a denial-of-service 
condition.

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-66364?


## How do I fix CVE-2026-66364?

No fix has been published for CVE-2026-66364 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-66364 being exploited?

There is no known exploitation of CVE-2026-66364 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-66364 and fix it if it is affected.

What it is: CVE-2026-66364 is a high-severity denial of service vulnerability in MZ Automation GmbH libiec61850, published on 30 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-66364 in the wild and no public exploit code.

Affected product: MZ Automation GmbH libiec61850. 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-2026-66364/ (Markdown: https://insights.sbomify.com/CVE-2026-66364/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-66364
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-66364
- OSV: https://osv.dev/vulnerability/CVE-2026-66364

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-66364/
Summaries are generated and may contain mistakes; the official description above is the record.