A critical stack-based buffer overflow vulnerability (CVE-2026-78012) has been identified in Pyramid Solutions NetStaX EtherNet/IP Stack versions prior to v5.6.1. The flaw allows a large Class 3 explicit-message request to exceed the application-side receive buffer without generating an error or warning. Successful exploitation could result in memory corruption, device crash, or a potential remote attack vector. All eight product variants of the NetStaX stack are affected, including adapter and scanner kits with and without CIP Security. The vulnerability carries a CVSS v3.1 score of 9.8 (CRITICAL) and a CVSS v4.0 score of 9.3 (CRITICAL). It impacts critical infrastructure sectors including Critical Manufacturing, Energy, Water and Wastewater, and Chemical industries worldwide. The fix is available in NetStaX v5.6.1, which implements compile-time assertions, runtime payload-size checks, and improved documentation. No known public exploitation has been reported to CISA at this time.
