RSLinx Classic is widely used in industrial control/automation; a remote-crafted CIP packet can crash the service, causing operational outages in ICS environments across multiple sectors.
CVE-2026-9621
RSLinx Classic service crash via crafted CIP packet causing DoS
Is CVE-2026-9621 being exploited?
Not confirmed. CVE-2026-9621 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.31% probability of exploitation in the next 30 days.
How severe is CVE-2026-9621?
CVE-2026-9621 is rated Critical with a CVSS score of 9.2. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-9621?
Yes. A fix has been recorded for CVE-2026-9621. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-9621 affect?
CVE-2026-9621 affects Rockwell Automation RSLinx Classic. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-9621?
Apply Rockwell patch immediately; restrict network access to RSLinx and monitor for malformed CIP traffic.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote denial-of-service: a crafted CIP packet crashes the RSLinx Classic service, interrupting ICS communications and requiring service restart, disrupting operations.
Immediate action required
- affectedV4.50 and prior
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.