No exploitation reportedFix available

CVE-2021-25661

Q: Is CVE-2021-25661 actively exploited?

Active exploitation of CVE-2021-25661 has not been confirmed. Its EPSS score was 1.1% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

Q: What is the CVSS score for CVE-2021-25661?

CVE-2021-25661 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

No exploitation reported by the sources we read.

Published2021-05-12
Fixed in16 · 15.1
WeaknessCWE-788

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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 has an out-of-bounds memory access vulnerability that could be triggered on the client side when sending data from the server, which could result in a Denial-of-Service condition.

Timeline

dates in UTC

2021-05-1214:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-25661?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-25661?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Siemens simatic hmi comfort outdoor panels 15\" firmwareversion to verify

Branch	Affected	Fixed in	Source
16.x	< 16	16	NVD
15.1	< 15.1	15.1	NVD
16.x	= 16	no fix published	NVD
15.1	= 15.1	no fix published	NVD

Siemens simatic hmi comfort outdoor panels 7\" firmwareversion to verify

Branch	Affected	Fixed in	Source
16.x	< 16	16	NVD
15.1	< 15.1	15.1	NVD
16.x	= 16	no fix published	NVD
15.1	= 15.1	no fix published	NVD

Siemens simatic hmi comfort panels 22\" firmwareversion to verify

Branch	Affected	Fixed in	Source
16.x	< 16	16	NVD
15.1	< 15.1	15.1	NVD
16.x	= 16	no fix published	NVD
15.1	= 15.1	no fix published	NVD

7 more products in the sources.

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Vendor advisories

ICSA-21-131-12 CISA8 known affected
Siemens SIMATIC SmartVNC HMI WinCC Products (Update B)
SIMATIC HMI Comfort Outdoor Panels V15 7" & 15" (incl. SIPLUS variants) · SIMATIC HMI Comfort Outdoor Panels V16 7" & 15" (incl. SIPLUS variants) · SIMATIC HMI Comfort Panels V15 4" - 22" (incl. SIPLUS variants) · +5 more

Full record on NVD

Fix

Update Siemens simatic hmi comfort outdoor panels 15\" firmware to 16 · 15.1
Vendor fix CISA ICSA-21-131-12 · 3 productsUpdate SIMATIC WinCC (TIA Portal) to V15.1 Update 6, and then update panel to V15.1 Update 6
Vendor fix CISA ICSA-21-131-12 · 3 productsUpdate SIMATIC WinCC (TIA Portal) to V16 Update 4 or later version, and then update panel to V16 Update 4 or later version
Vendor fix CISA ICSA-21-131-12 · 1 productUpdate to V15.1 Update 6
Vendor fix CISA ICSA-21-131-12 · 1 productUpdate to V16 Update 4 or later version
Mitigation from the vendor CISA ICSA-21-131-12 · 8 productsRestrict access to port 5900/tcp to trusted IP addresses only

Advisories and patches

cert-portal.siemens.comVendor Advisory

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

CISA-ADPSSVC decisionnone2026-06-02
OpenCVESSVC decisionnone—
CISA-ADPCVSS 3.17.52026-06-02
NVDCVSS 3.17.5read 2026-10-23
NVDCVSS 2.05read 2026-10-23
CNAweakness (CWE)CWE-788read 2026-10-23
FIRST EPSSEPSS score1.1 %2026-10-22

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published: 2021-05-12
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2021-25661?

Is CVE-2021-25661 actively exploited?

Active exploitation of CVE-2021-25661 has not been confirmed. Its EPSS score was 1.1% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-25661?

CVE-2021-25661 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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Surveillance reads the versions in your stack — a domain, a lockfile or a list — checks each CVE against the ranges its sources publish, and alerts you when one you run is exploited or enters CISA KEV. A version it cannot read stays « version not verified ».

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