Rockwell Automation RSLinx Classic

Summary

Rockwell Automation has released a fix for multiple denial-of-service vulnerabilities in its RSLinx Classic software, affecting versions 4.50 and earlier. Exploitation of these flaws, stemming from improper handling of crafted CIP packets, could lead to service crashes and require restarts. The vulnerabilities have been assigned CVE identifiers CVE-2026-9621, CVE-2026-9622, CVE-2026-9624, and CVE-2026-9625, with CVSS scores indicating high severity.

Full text

ICS Advisory Rockwell Automation RSLinx Classic Release DateSeptember 01, 2026 Alert CodeICSA-26-244-01 Related topics: Industrial Control System Vulnerabilities , Industrial Control Systems View CSAF Summary Successful exploitation of these vulnerabilities could allow an attacker to cause a denial-of-service condition on the affected product. The following versions of Rockwell Automation RSLinx Classic are affected: RSLinx Classic <=4.50 (CVE-2026-9621, CVE-2026-9622, CVE-2026-9624, CVE-2026-9625) CVSS Vendor Equipment Vulnerabilities v3 8.6 Rockwell Automation Rockwell Automation RSLinx Classic Integer Overflow or Wraparound, Integer Underflow (Wrap or Wraparound), Buffer Copy without Checking Size of Input ('Classic Buffer Overflow') Background Critical Infrastructure Sectors: Critical Manufacturing Countries/Areas Deployed: Worldwide Company Headquarters Location: United States Vulnerabilities Expand All + CVE-2026-9621 A denial-of-service security issue exists within RSLinx Classic. The security issue stems from improper handling of a malformed packet. A crafted CIP packet can cause the RSLinx Classic service to crash, requiring a restart of the service to recover. View CVE Details Affected Products Rockwell Automation RSLinx Classic Vendor:Rockwell Automation Product Version:Rockwell Automation RSLinx Classic: <=4.50 Product Status:known_affected Remediations Vendor fixRockwell Automation has corrected the vulnerabilities in RSLinx Classic version 4.60. MitigationUsers using the affected software, who are not able to upgrade to one of the corrected versions, should use Rockwell Automation's security best practices https://support.rockwellautomation.com/app/answers/answer_view/a_id/1085012/loc/en_US#__highlight.https://support.rockwellautomation.com/app/answers/answer_view/a_id/1085012/loc/en_US#__highlight MitigationFor more information, see Rockwell Automation Security Advisories: https://www.rockwellautomation.com/en-us/trust-center/security-advisories.html.https://www.rockwellautomation.com/en-us/trust-center/security-advisories.html Relevant CWE: CWE-190 Integer Overflow or Wraparound Metrics CVSS Version Base Score Base Severity Vector String 3.1 8.6 HIGH CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H 4.0 9.2 CRITICAL CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H CVE-2026-9622 A denial-of-service security issue exists within RSLinx Classic. A crafted CIP packet targeting the Forward Close service can cause the RSLinx Classic service to crash, requiring a restart of the service to recover. View CVE Details Affected Products Rockwell Automation RSLinx Classic Vendor:Rockwell Automation Product Version:Rockwell Automation RSLinx Classic: <=4.50 Product Status:known_affected Remediations Vendor fixRockwell Automation has corrected the vulnerabilities in RSLinx Classic version 4.60. MitigationUsers using the affected software, who are not able to upgrade to one of the corrected versions, should use Rockwell Automation's security best practices https://support.rockwellautomation.com/app/answers/answer_view/a_id/1085012/loc/en_US#__highlight.https://support.rockwellautomation.com/app/answers/answer_view/a_id/1085012/loc/en_US#__highlight MitigationFor more information, see Rockwell Automation Security Advisories: https://www.rockwellautomation.com/en-us/trust-center/security-advisories.html.https://www.rockwellautomation.com/en-us/trust-center/security-advisories.html Relevant CWE: CWE-191 Integer Underflow (Wrap or Wraparound) Metrics CVSS Version Base Score Base Severity Vector String 3.1 8.6 HIGH CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H 4.0 9.2 CRITICAL CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H CVE-2026-9624 A denial-of-service security issue exists within RSLinx Classic. A crafted CIP packet can cause the RSLinx Classic service to crash due to insufficient data length validation, requiring a restart of the service to recover. View CVE Details Affected Products Rockwell Automation RSLinx Classic Vendor:Rockwell Automation Product Version:Rockwell Automation RSLinx Classic: <=4.50 Product Status:known_affected Remediations Vendor fixRockwell Automation has corrected the vulnerabilities in RSLinx Classic version 4.60. MitigationUsers using the affected software, who are not able to upgrade to one of the corrected versions, should use Rockwell Automation's security best practices https://support.rockwellautomation.com/app/answers/answer_view/a_id/1085012/loc/en_US#__highlight.https://support.rockwellautomation.com/app/answers/answer_view/a_id/1085012/loc/en_US#__highlight MitigationFor more information, see Rockwell Automation Security Advisories: https://www.rockwellautomation.com/en-us/trust-center/security-advisories.html.https://www.rockwellautomation.com/en-us/trust-center/security-advisories.html Relevant CWE: CWE-191 Integer Underflow (Wrap or Wraparound) Metrics CVSS Version Base Score Base Severity Vector String 3.1 7.5 HIGH CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H 4.0 8.7 HIGH CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N CVE-2026-9625 A denial-of-service security issue exists within RSLinx Classic. A crafted CIP packet with an oversized embedded message request can cause the RSLinx Classic service to crash, requiring a restart of the service to recover. View CVE Details Affected Products Rockwell Automation RSLinx Classic Vendor:Rockwell Automation Product Version:Rockwell Automation RSLinx Classic: <=4.50 Product Status:known_affected Remediations Vendor fixRockwell Automation has corrected the vulnerabilities in RSLinx Classic version 4.60. MitigationUsers using the affected software, who are not able to upgrade to one of the corrected versions, should use Rockwell Automation's security best practices https://support.rockwellautomation.com/app/answers/answer_view/a_id/1085012/loc/en_US#__highlight.https://support.rockwellautomation.com/app/answers/answer_view/a_id/1085012/loc/en_US#__highlight MitigationFor more information, see Rockwell Automation Security Advisories: https://www.rockwellautomation.com/en-us/trust-center/security-advisories.html.https://www.rockwellautomation.com/en-us/trust-center/security-advisories.html Relevant CWE: CWE-120 Buffer Copy without Checking Size of Input ('Classic Buffer Overflow') Metrics CVSS Version Base Score Base Severity Vector String 3.1 7.5 HIGH CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H 4.0 8.7 HIGH CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N Acknowledgments Rockwell Automation reported these vulnerabilities to CISA Legal Notice and Terms of Use This product is provided subject to this Notification (https://www.cisa.gov/notification) and this Privacy & Use policy (https://www.cisa.gov/privacy-policy). Recommended Practices CISA recommends users take defensive measures to minimize the risk of exploitation of these vulnerabilities. Minimize network exposure for all control system devices and/or systems, ensuring they are not accessible from the internet. Locate control system networks and remote devices behind firewalls and isolating them from business networks. When remote access is required, use more secure methods, such as Virtual Private Networks (VPNs), recognizing VPNs may have vulnerabilities and should be updated to the most current version available. Also recognize VPN is only as secure as the connected devices. CISA reminds organizations to perform proper impact analysis and risk assessment prior to deploying defensive measures. CISA also provides a section for control systems security recommended practices on the ICS webpage on cisa.gov/ics. Several CISA products detailing cyber defense best practices are available for reading and download, including Improving Industrial Control Systems Cybersecurity with Defense-in-Depth Strategies. CISA encourages organizations to implement recommended cybersecurity strategies for proactive defense of ICS assets. Additional mitigation guidance and recommended p

Indicators of Compromise

• cve — CVE-2026-9621
• cve — CVE-2026-9622
• cve — CVE-2026-9624
• cve — CVE-2026-9625

Entities