No exploitation reportedFix available

CVE-2021-31889

Q: Is CVE-2021-31889 actively exploited?

Active exploitation of CVE-2021-31889 has not been confirmed. Its EPSS score was 2.2% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

Q: What is the CVSS score for CVE-2021-31889?

CVE-2021-31889 has a CVSS v3 base score of 9.1 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H.

No exploitation reported by the sources we read.

Published2021-11-09
WeaknessCWE-191

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 Capital Embedded AR Classic 431-422 (All versions), Capital Embedded AR Classic R20-11 (All versions < V2303), PLUSCONTROL 1st Gen (All versions), SIMOTICS CONNECT 400 (All versions < V0.5.0.0). Malformed TCP packets with a corrupted SACK option leads to Information Leaks and Denial-of-Service conditions. (FSMD-2021-0015)

Timeline

dates in UTC

2021-11-0912:15CVE 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-2021-31889?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-31889?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Siemens apogee modular building controller firmwareversion to verify

Branch	Affected	Fixed in	Source
—	all versions	no fix published	NVD

Siemens apogee modular equiment controller firmwareversion to verify

Branch	Affected	Fixed in	Source
—	all versions	no fix published	NVD

Siemens apogee pxc compact firmwareversion to verify

Branch	Affected	Fixed in	Source
—	all versions	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-22-069-02 CISA1 known affected
Siemens SIMOTICS CONNECT 400
SIMOTICS CONNECT 400
ICSA-22-013-03 CISA1 known affected
Siemens Energy PLUSCONTROL
PLUSCONTROL 1st Gen
ICSA-21-350-06 CISA2 known affected
Siemens Capital VSTAR
Capital Embedded AR Classic 431-422 · Capital Embedded AR Classic R20-11
ICSA-21-313-03 CISA3 known affected
Siemens Nucleus RTOS TCP/IP Stack
Nucleus NET · Nucleus ReadyStart V3 · Nucleus Source Code
ICSA-21-315-07 CISA23 known affected
Siemens Nucleus RTOS-based APOGEE and TALON Products (Update C)
APOGEE MBC (PPC) (BACnet) · APOGEE MBC (PPC) (P2 Ethernet) · APOGEE MEC (PPC) (BACnet) · +20 more

Full record on NVD

Fix

Vendor fix CISA ICSA-22-069-02 · 1 productUpdate to V0.5.0.0 or later version
Vendor fix CISA ICSA-21-350-06 · 1 productUpdate to V2303 or later version
Vendor fix CISA ICSA-21-313-03 · 1 productUpdate to V2017.02.4 or later version
Vendor fix CISA ICSA-21-313-03 · 1 productContact customer support to receive patch and update information
Vendor fix CISA ICSA-21-315-07 · 4 productsUpdate to V3.5.4 or later version
Vendor fix CISA ICSA-21-315-07 · 2 productsUpdate to V2.8.19 or later version

Advisories and patches

cert-portal.siemens.comVendor Advisory
cert-portal.siemens.comVendor Advisory

Detection

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

Sources

CNACVSS 3.17.5read 2026-10-23
NVDCVSS 3.19.1read 2026-10-23
NVDCVSS 2.06.4read 2026-10-23
CNAweakness (CWE)CWE-191read 2026-10-23
FIRST EPSSEPSS score2.2 %2026-10-22

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
Published: 2021-11-09
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2021-31889?

Is CVE-2021-31889 actively exploited?

Active exploitation of CVE-2021-31889 has not been confirmed. Its EPSS score was 2.2% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-31889?

CVE-2021-31889 has a CVSS v3 base score of 9.1 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H.

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