How severe is CVE-2021-31337?

CVE-2021-31337 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-31337 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (74th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-31337?

CVE-2021-31337 primarily affects Siemens Sinamics Sl150 Firmware. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-31337?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2021-31337 published?

CVE-2021-31337 was published on 2021-06-28 and last updated on 2026-06-17.

CVE-2021-31337

CVE-2021-31337 is a critical-severity vulnerability in Siemens Sinamics Sl150 Firmware with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-306.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 6.8
EPSS exploit prediction: 2% (74th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-306
Affected product: Siemens Sinamics Sl150 Firmware
Published: 2021-06-28
Last modified: 2026-06-17

Description

The Telnet service of the SIMATIC HMI Comfort Panels system component in affected products does not require authentication, which may allow a remote attacker to gain access to the device if the service is enabled. Telnet is disabled by default on the SINAMICS Medium Voltage Products (SINAMICS SL150: All versions, SINAMICS SM150: All versions, SINAMICS SM150i: All versions).

Frequently asked questions

What is CVE-2021-31337?: The Telnet service of the SIMATIC HMI Comfort Panels system component in affected products does not require authentication, which may allow a remote attacker to gain access to the device if the service is enabled. Telnet is disabled by default on the SINAMICS Medium Voltage Products (SINAMICS SL150: All versions, SINAMICS SM150: All versions, SINAMICS SM150i: All versions).
How severe is CVE-2021-31337?: CVE-2021-31337 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-31337 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (74th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-31337?: CVE-2021-31337 primarily affects Siemens Sinamics Sl150 Firmware. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-31337?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-31337 published?: CVE-2021-31337 was published on 2021-06-28 and last updated on 2026-06-17.

References

https://us-cert.cisa.gov/ics/advisories/icsa-21-131-04

Affected products (3)

cpe:2.3:o:siemens:sinamics_sl150_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:sinamics_sm150_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:sinamics_sm150i_firmware:*:*:*:*:*:*:*:*

More vulnerabilities in Siemens Sinamics Sl150 Firmware

CVE-2021-27388 — Critical (CVSS 9.8): SINAMICS medium voltage routable products are affected by a vulnerability in the Sm@rtServer component for remote…
CVE-2021-27384 — Critical (CVSS 9.8): A vulnerability has been identified in SIMATIC HMI Comfort Outdoor Panels V15 7\" & 15\" (incl. SIPLUS variants) (All…
CVE-2020-15798 — Critical (CVSS 9.8): A vulnerability has been identified in SIMATIC HMI Comfort Panels (incl. SIPLUS variants) (All versions < V16 Update…
CVE-2021-27386 — High (CVSS 7.5): A vulnerability has been identified in SIMATIC HMI Comfort Outdoor Panels V15 7\" & 15\" (incl. SIPLUS variants) (All…
CVE-2021-27385 — High (CVSS 7.5): A vulnerability has been identified in SIMATIC HMI Comfort Outdoor Panels V15 7\" & 15\" (incl. SIPLUS variants) (All…
CVE-2021-27383 — High (CVSS 7.5): A vulnerability has been identified in SIMATIC HMI Comfort Outdoor Panels V15 7\" & 15\" (incl. SIPLUS variants) (All…

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