# CVE-2026-65421: MZ Automation libiec61850 heap out-of-bounds read in MMS BER decoder

Source: https://junglewise.ai/threats/cve-2026-65421-mz-automation-libiec61850-heap-out-of-bounds-read-in-mms-ber  
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-2026-65421 · Severity: medium · CVSS 6.5 · Published 2026-07-30

MZ Automation libiec61850 is a software library used in the energy sector to implement communication protocols for electrical substation automation. A vulnerability in how the library handles specific data messages allows an attacker on the same local network to crash the service. This results in a denial-of-service condition, potentially disrupting the monitoring and control of critical power infrastructure.

## Quick answers

**Is CVE-2026-65421 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-65421 being exploited in the wild.

**How severe is CVE-2026-65421?** 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-2026-65421?** A patch was published on 2026-07-30. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-65421 attacked?** It is attacked from the adjacent network, in a software library.

**Am I affected by CVE-2026-65421?** 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

An out-of-bounds read vulnerability exists in the MMS BER decoder component of libiec61850. The flaw is located in the decoding logic for fixed-width Basic Encoding Rules (BER) fields, specifically booleans and integers. The decoder fails to validate attacker-supplied length values, leading to a read past the end of a heap buffer. An unauthenticated attacker on the adjacent network can exploit this by sending a specially crafted message, causing the MMS service process to terminate and resulting in a denial-of-service (DoS). The vulnerability is addressed in version 1.6.2.

## Affected products

- MZ Automation GmbH libiec61850 < 1.6.2

## Timeline

- 2026-07-30: advisory
- 2026-07-30: patched

## 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)