# CVE-2026-66349: MZ Automation libiec61850 heap out-of-bounds read in MMS server

Source: https://junglewise.ai/threats/cve-2026-66349-mz-automation-libiec61850-heap-out-of-bounds-read-in-mms-server  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-30. Updated: 2026-07-30  
License: CC BY 4.0 with a link back

CVE-2026-66349 · Severity: medium · CVSS 6.5 · Published 2026-07-30

A vulnerability exists in a widely used communication library for electrical substation automation. An attacker on the same local network can send a specially crafted message to a device using this library, causing the system to crash. This results in a denial-of-service, potentially disrupting critical infrastructure operations and monitoring.

## Quick answers

**Is CVE-2026-66349 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-66349 being exploited in the wild.

**How severe is CVE-2026-66349?** Medium severity, with a CVSS score of 6.5, published 30 July 2026.

**Which products and versions are affected?** MZ Automation GmbH libiec61850 < 1.6.2.

**Is there a fix for CVE-2026-66349?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-66349 attacked?** It is attacked from the adjacent network, in a software library.

**Am I affected by CVE-2026-66349?** Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The MMS server connection handler in libiec61850 (versions prior to 1.6.2) contains a flaw in its BER-encoded request data processing. When an MMS confirmed request PDU containing an extended BER tag is received over an established session, the decoder fails to perform a proper bounds check. This missing check causes the decoder to advance its internal buffer incorrectly, resulting in a one-byte heap out-of-bounds read. An attacker with adjacent network access can exploit this to terminate the MMS service process, causing a denial-of-service (DoS) condition. The issue is addressed in version 1.6.2.

## Affected products

- MZ Automation GmbH libiec61850 < 1.6.2

## Timeline

- 2026-07-30: disclosed
- 2026-07-30: advisory

## References

- [https://github.com/cisagov/CSAF/blob/develop/csaf_files/OT/white/2026/icsa-26-211-10.json](https://github.com/cisagov/CSAF/blob/develop/csaf_files/OT/white/2026/icsa-26-211-10.json)
- [https://www.cisa.gov/news-events/ics-advisories/icsa-26-211-10](https://www.cisa.gov/news-events/ics-advisories/icsa-26-211-10)