# CVE-2026-9621: Rockwell Automation RSLinx Classic denial-of-service via malformed CIP packet

Source: https://junglewise.ai/threats/cve-2026-9621-rockwell-automation-rslinx-classic-denial-of-service-via-malformed  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-01. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-9621 · Severity: info · CVSS 8.6 · Published 2026-09-01

RSLinx Classic is communications software from Rockwell Automation used to connect industrial automation devices and systems in manufacturing and control environments. A malformed network packet can crash the RSLinx service, causing loss of connectivity and requiring manual service restart to restore operations.

Technologies: [Rockwell Automation RSLinx Classic](https://junglewise.ai/threats/technologies/rslinx-classic). Vendors: [Rockwell Automation](https://junglewise.ai/threats/vendors/rockwell-automation).

## Quick answers

**Is CVE-2026-9621 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-9621 being exploited in the wild.

**How severe is CVE-2026-9621?** Informational severity, with a CVSS score of 8.6, published 1 September 2026.

**Which products and versions are affected?** Rockwell Automation RSLinx Classic V4.50 and prior.

**Is there a fix for CVE-2026-9621?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-9621 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-9621?** Check whether you run Rockwell Automation RSLinx Classic at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

CVE-2026-9621 is a denial-of-service vulnerability caused by improper handling of malformed CIP (Common Industrial Protocol) packets in RSLinx Classic. The root cause is an integer overflow (CWE-190) in packet parsing logic. An unauthenticated remote attacker can send a specially crafted CIP packet to the service to trigger a crash. No workarounds are available; affected versions V4.50 and prior must be upgraded to V4.60 or later to remediate.

## Affected products

- Rockwell Automation RSLinx Classic V4.50 and prior

## Timeline

- 2026-09-01: disclosed

## References

- [https://www.rockwellautomation.com/en-us/trust-center/security-advisories/advisory.SD1794.html](https://www.rockwellautomation.com/en-us/trust-center/security-advisories/advisory.SD1794.html)

## Related threats

- [Rockwell Automation RSLinx Classic denial-of-service in CIP packet handling](https://junglewise.ai/threats/cve-2026-9625-rockwell-automation-rslinx-classic-denial-of-service-in-cip-packet)
- [Rockwell Automation RSLinx Classic denial-of-service via malformed CIP packet](https://junglewise.ai/threats/cve-2026-9624-rockwell-automation-rslinx-classic-denial-of-service-via-malformed)
- [Rockwell Automation RSLinx Classic denial-of-service in Forward Close service](https://junglewise.ai/threats/cve-2026-9622-rockwell-automation-rslinx-classic-denial-of-service-in-forward)