CVE-2026-9307: CompactLogix Information Disclosure Flaw

CVE-2026-9307 Overview

CVE-2026-9307 is an information disclosure vulnerability affecting Rockwell Automation CompactLogix controllers. The controller's embedded web server exposes Common Industrial Protocol (CIP) Connection IDs on the diagnostics webpage. Any unauthenticated user with network access can retrieve this data. Attackers can leverage the exposed Connection IDs to craft malicious CIP packets that disrupt established sessions, producing a Denial-of-Service condition on the controller. The issue is classified under [CWE-497] (Exposure of Sensitive System Information to an Unauthorized Control Sphere). Because CompactLogix controllers are deployed in operational technology (OT) environments, exploitation can interrupt industrial processes.

Critical Impact
Unauthenticated network attackers can harvest CIP Connection IDs from the diagnostics page and use them to construct packets that trigger a Denial-of-Service against industrial control processes.

Affected Products

Rockwell Automation CompactLogix controllers (per vendor advisory SD1776)
CompactLogix controller embedded web server diagnostics interface
CIP-based communication sessions managed by affected firmware

Discovery Timeline

2026-06-16 - CVE-2026-9307 published to the National Vulnerability Database
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2026-9307

Vulnerability Analysis

The affected CompactLogix controllers run an embedded HTTP server that provides diagnostic information for operators. The diagnostics webpage includes CIP Connection IDs for active sessions, and the page is reachable without authentication. CIP Connection IDs are session identifiers used by the Common Industrial Protocol to route messages between endpoints over EtherNet/IP. When these identifiers are visible to outside parties, they break an implicit trust boundary that the protocol relies on for in-session message validation.

An attacker who reads the diagnostics page can enumerate active connections and then forge CIP traffic referencing those identifiers. Crafted packets can desynchronize or terminate sessions between the controller and engineering or HMI clients, halting process control communication. The result is a loss of availability on the controller, which in OT environments translates into downtime for the underlying physical process.

Root Cause

The root cause is improper exposure of internal session metadata through an unauthenticated diagnostic interface [CWE-497]. The web server treats Connection IDs as non-sensitive diagnostic data and renders them on a page accessible to any network peer. There is no access control wrapping the diagnostics endpoint and no obfuscation of session-bound identifiers.

Attack Vector

Exploitation requires network reachability to the controller's web server, typically TCP port 80 or 443 on the EtherNet/IP interface. The attacker issues an HTTP GET request to the diagnostics page and parses the returned CIP Connection IDs. The attacker then sends forged CIP packets over EtherNet/IP that reference the harvested identifiers, causing the controller to drop or mishandle legitimate sessions. No credentials, user interaction, or local access are required, though some attack complexity exists in correctly crafting the follow-on CIP traffic. See the Rockwell Automation Security Advisory SD1776 for vendor-specific technical detail.

Detection Methods for CVE-2026-9307

Indicators of Compromise

Unexpected HTTP GET requests to the CompactLogix controller diagnostics page from non-engineering hosts.
CIP session resets or connection timeouts observed by HMI or engineering workstations without corresponding operational changes.
Repeated EtherNet/IP traffic from a single source referencing multiple Connection IDs in short succession.
Web server access logs showing unauthenticated diagnostic page reads from outside the OT management VLAN.

Detection Strategies

Monitor north-south and east-west traffic to controller IP addresses for HTTP requests targeting diagnostic URIs.
Deploy OT-aware intrusion detection rules that flag CIP traffic from unauthorized source addresses.
Correlate controller availability events with prior HTTP reconnaissance against the same device.
Baseline normal CIP Connection ID lifetimes and alert on premature terminations.

Monitoring Recommendations

Capture EtherNet/IP traffic at switches connected to CompactLogix controllers and retain for forensic review.
Forward controller web server access logs, where available, to a centralized SIEM for anomaly analysis.
Track controller process scan times and communication health metrics for sudden degradation.

How to Mitigate CVE-2026-9307

Immediate Actions Required

Restrict network access to CompactLogix controllers using firewall rules that allow only authorized engineering hosts.
Disable the controller's embedded web server if it is not operationally required.
Segment the OT network from corporate IT and remote-access pathways per ISA/IEC 62443 zones and conduits.
Audit existing access logs and CIP session telemetry for prior reconnaissance against the diagnostics page.

Patch Information

Rockwell Automation has published guidance in advisory SD1776. Apply the firmware updates listed in the Rockwell Automation Security Advisory for the specific CompactLogix catalog numbers and firmware revisions deployed in your environment. Validate updates in a non-production environment before promoting to production controllers.

Workarounds

Place affected controllers behind an industrial firewall and restrict TCP/80 and TCP/443 to a defined allow list.
Disable HTTP diagnostics where the feature is not actively used by maintenance teams.
Apply CIP traffic filtering on industrial DMZ devices to drop unsolicited EtherNet/IP packets from untrusted sources.
Enforce strict VLAN separation between control networks and any user-accessible network segments.

bash

# Example: restrict HTTP access to CompactLogix controllers using iptables on an upstream gateway
iptables -A FORWARD -p tcp -d 10.10.20.0/24 --dport 80  -s 10.10.30.50 -j ACCEPT
iptables -A FORWARD -p tcp -d 10.10.20.0/24 --dport 443 -s 10.10.30.50 -j ACCEPT
iptables -A FORWARD -p tcp -d 10.10.20.0/24 --dport 80  -j DROP
iptables -A FORWARD -p tcp -d 10.10.20.0/24 --dport 443 -j DROP