CVE-2021-25662 Denial of service in SIMATIC HMI Comfort Outdoor Panels V15 7\" & 15\" (incl. SIPLUS variants)

Q: Is CVE-2021-25662 being exploited?

There is no known exploitation of CVE-2021-25662 in the wild and no public exploit code.

Q: How do I fix CVE-2021-25662?

No fix has been published for CVE-2021-25662 yet. Limit exposure of the affected software until one is available.

High 7.5 Published 12 May 2021 Updated 2 Jun 2026

A flaw in the SmartVNC client allows a remote attacker to cause a denial-of-service condition by sending a modified packet, affecting Siemens HMI panels and WinCC Runtime.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: None listed

What is CVE-2021-25662?

CVE-2021-25662 is a high-severity denial of service vulnerability in Siemens SIMATIC HMI Comfort Outdoor Panels V15 7\" & 15\" (incl. SIPLUS variants), published on 12 May 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

A vulnerability has been identified in SIMATIC HMI Comfort Outdoor Panels V15 7\" & 15\" (incl. SIPLUS variants) (All versions < V15.1 Update 6), SIMATIC HMI Comfort Outdoor Panels V16 7\" & 15\" (incl. SIPLUS variants) (All versions < V16 Update 4), SIMATIC HMI Comfort Panels V15 4\" - 22\" (incl. SIPLUS variants) (All versions < V15.1 Update 6), SIMATIC HMI Comfort Panels V16 4\" - 22\" (incl. SIPLUS variants) (All versions < V16 Update 4), SIMATIC HMI KTP Mobile Panels V15 KTP400F, KTP700, KTP700F, KTP900 and KTP900F (All versions < V15.1 Update 6), SIMATIC HMI KTP Mobile Panels V16 KTP400F, KTP700, KTP700F, KTP900 and KTP900F (All versions < V16 Update 4), SIMATIC WinCC Runtime Advanced V15 (All versions < V15.1 Update 6), SIMATIC WinCC Runtime Advanced V16 (All versions < V16 Update 4). SmartVNC client fails to handle an exception properly if the program execution process is modified after sending a packet from the server, which could result in a Denial-of-Service condition.

Weakness: CWE-755

Which versions are affected by CVE-2021-25662?

It affects 10 products.

Products include Siemens Simatic Hmi Comfort Outdoor Panels 15\" Firmware, Siemens Simatic Hmi Comfort Outdoor Panels 7\" Firmware, Siemens Simatic Hmi Comfort Panels 22\" Firmware, Siemens Simatic Hmi Comfort Panels 4\" Firmware, Siemens Simatic Hmi Ktp Mobile Panels Ktp400f Firmware, Siemens Simatic Hmi Ktp Mobile Panels Ktp700 Firmware and 4 more.

How do I fix CVE-2021-25662?

No fix has been published for CVE-2021-25662 yet. Limit exposure of the affected software until one is available.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2021-25662 being exploited?

There is no known exploitation of CVE-2021-25662 in the wild and no public exploit code.

Sources

Also known as GHSA-444h-8mr2-wm66.