CVE-2021-22681: FactoryTalk Auth Bypass Vulnerability

CVE-2021-22681 Overview

CVE-2021-22681 is a critical authentication bypass vulnerability affecting Rockwell Automation Studio 5000 Logix Designer and RSLogix 5000 software, along with multiple Logix controller families. The vulnerability exists in the authentication mechanism used to verify communications between the engineering software and programmable logic controllers (PLCs). An unauthenticated remote attacker can bypass the verification mechanism and establish unauthorized connections to affected industrial control system (ICS) devices.

This vulnerability is particularly concerning for industrial control system environments, as successful exploitation could allow attackers to manipulate PLC logic, disrupt manufacturing processes, or cause physical damage to industrial equipment.

Critical Impact

Unauthenticated remote attackers can bypass authentication and gain unauthorized access to industrial control systems, potentially allowing manipulation of critical manufacturing and process control operations.

Affected Products

• Rockwell Automation Studio 5000 Logix Designer Versions 21 and later
• Rockwell Automation RSLogix 5000 Versions 16 through 20
• Rockwell Automation CompactLogix 1768, 1769, 5370, 5380, 5480
• Rockwell Automation ControlLogix 5550, 5560, 5570, 5580
• Rockwell Automation DriveLogix 5560, 5730, 1794-L34
• Rockwell Automation Compact GuardLogix 5370, 5380
• Rockwell Automation GuardLogix 5570, 5580
• Rockwell Automation SoftLogix 5800
• Rockwell Automation FactoryTalk Services Platform

Discovery Timeline

• March 3, 2021 - CVE-2021-22681 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2021-22681

Vulnerability Analysis

This vulnerability falls under CWE-522 (Insufficiently Protected Credentials), indicating a fundamental weakness in how the authentication mechanism protects sensitive credential information. The Logix controllers use a shared cryptographic key to verify that engineering workstations running Studio 5000 Logix Designer or RSLogix 5000 are authorized to communicate with the controllers.

The authentication bypass allows unauthenticated attackers with network access to completely circumvent the verification mechanism. Once bypassed, attackers can authenticate to the affected controllers as if they were legitimate engineering workstations. This grants them the ability to download or modify PLC programs, change controller configurations, and potentially disrupt industrial processes.

The network-accessible nature of this vulnerability means that any attacker who can reach the affected controllers over the network can attempt exploitation without requiring prior authentication or user interaction.

Root Cause

The root cause of CVE-2021-22681 lies in the insufficiently protected credentials used for controller authentication. The cryptographic key used to verify legitimate communications between Rockwell Automation engineering software and Logix controllers can be bypassed by an attacker. This represents a fundamental design flaw in the authentication architecture rather than a simple implementation bug.

The verification mechanism fails to adequately protect the authentication credentials, allowing attackers to forge or bypass the authentication process entirely. This design weakness affects the entire family of affected Logix controllers and associated engineering software.

Attack Vector

The attack vector for CVE-2021-22681 is network-based, meaning attackers must have network connectivity to the targeted Logix controllers. In industrial environments, this typically requires either:

1. Access to the operational technology (OT) network segment where PLCs reside
2. Exploitation of network segmentation weaknesses that expose ICS devices to broader network access
3. Compromise of a system with dual-homed access to both IT and OT networks

Once network access is established, the attacker can communicate directly with the affected controllers using the Rockwell Automation communication protocols. By exploiting the authentication bypass, the attacker can establish a connection that appears to be from a legitimate engineering workstation.

The attacker can then perform actions such as reading controller configurations, modifying ladder logic programs, changing setpoints, or issuing commands that could affect physical processes controlled by the PLCs.

Detection Methods for CVE-2021-22681

Indicators of Compromise

• Unauthorized connection attempts to Logix controllers from unexpected IP addresses or workstations
• Anomalous EtherNet/IP or CIP protocol traffic to PLC communication ports
• Unexpected changes to PLC programs, configurations, or firmware
• Controller mode changes (Run/Program/Remote) without corresponding authorized activity logs

Detection Strategies

• Deploy network monitoring solutions capable of deep packet inspection of industrial protocols including EtherNet/IP and CIP
• Implement allowlisting of authorized engineering workstations permitted to communicate with Logix controllers
• Enable and monitor controller audit logs for unauthorized access attempts or configuration changes
• Deploy industrial-aware intrusion detection systems (IDS) at network segmentation points

Monitoring Recommendations

• Continuously monitor network traffic between engineering workstations and Logix controllers for anomalies
• Establish baseline communication patterns and alert on deviations from normal controller access patterns
• Monitor for unauthorized firmware uploads or logic changes to controllers
• Implement centralized logging and SIEM integration for all ICS network traffic and controller events

How to Mitigate CVE-2021-22681

Immediate Actions Required

• Review and harden network segmentation between IT and OT networks to limit exposure of affected controllers
• Implement strict access controls and firewall rules restricting which systems can communicate with Logix controllers
• Disable any unnecessary network services on affected controllers
• Conduct an inventory of all affected Rockwell Automation products in your environment and prioritize remediation

Patch Information

Rockwell Automation has released guidance and mitigations for this vulnerability. Organizations should consult the CISA ICS Advisory ICSA-21-056-03 for detailed remediation steps and apply any available firmware updates or configuration changes recommended by Rockwell Automation.

Contact Rockwell Automation technical support for specific patch information and updated firmware versions for affected controller families. Due to the critical nature of this vulnerability, prioritize remediation for any internet-exposed or inadequately segmented controllers.

Workarounds

• Implement CIP Security features where supported by controller firmware versions to add an additional layer of authentication
• Use hardware key switches on controllers to physically prevent unauthorized program changes
• Deploy application-layer firewalls capable of filtering and validating industrial protocol communications
• Restrict physical and logical access to engineering workstations that communicate with affected controllers

# Example firewall rule to restrict controller access (adapt to your firewall platform)
# Allow only authorized engineering workstations to reach Logix controllers
iptables -A INPUT -p tcp --dport 44818 -s 192.168.10.50 -j ACCEPT
iptables -A INPUT -p tcp --dport 44818 -s 192.168.10.51 -j ACCEPT
iptables -A INPUT -p tcp --dport 44818 -j DROP