XSS Flaw Found in OpenPLC Runtime v3

A CISA advisory details an XSS vulnerability in OpenPLC Runtime v3 that lets attackers hijack operator sessions to control PLCs; no vendor patch as v3 is end-of-life.

CISA published an ICS advisory for OpenPLC Runtime v3, developed by Autonomy Logic, disclosing CVE-2026-88020, a reflected cross-site scripting (XSS) vulnerability (CWE-79) in the product's web interface. The flaw stems from improper neutralization of a query string parameter used for routing within the web page generation logic, allowing an attacker to inject malicious content. Successful exploitation could allow an attacker to hijack an operator's session cookies and issue state-changing requests, effectively granting control over the programmable logic controller (PLC) and the physical processes it manages.

OpenPLC is deployed worldwide across critical infrastructure sectors including Critical Manufacturing, Energy, Transportation Systems, and Water and Wastewater Systems. Because OpenPLC v3 has reached end-of-life, Autonomy Logic will not issue a patch and instead recommends users upgrade to OpenPLC v4. CISA reports no known public exploitation of this vulnerability at this time and recommends standard ICS defensive measures: minimizing internet exposure of control system devices, isolating ICS networks behind firewalls, and using secure remote access methods such as VPNs.

The vulnerability was responsibly reported to CISA by researchers Rajivarnan R. and Shirshak of Secnora. Given the lack of an available patch, defenders running OpenPLC v3 should prioritize network segmentation and migration planning to v4, and monitor web interface access logs for anomalous query string parameters indicative of XSS attempts.

Source reporting: https://www.cisa.gov/news-events/ics-advisories/icsa-26-265-09