How severe is CVE-2021-37186?

CVE-2021-37186 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over an adjacent network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2021-37186 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (28th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-37186?

CVE-2021-37186 primarily affects Siemens Logo! Cmr2020 Firmware. In total, 6 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-37186?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-37186 published?

CVE-2021-37186 was published on 2021-09-14 and last updated on 2026-06-17.

CVE-2021-37186

CVE-2021-37186 is a medium-severity vulnerability in Siemens Logo! Cmr2020 Firmware with a CVSS 3.x base score of 5.4. 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-330.

Key facts

Severity: Medium (CVSS 3.x base score 5.4)
CVSS v2: 4.8
EPSS exploit prediction: 0% (28th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-330
Affected product: Siemens Logo! Cmr2020 Firmware
Published: 2021-09-14
Last modified: 2026-06-17

Description

A vulnerability has been identified in LOGO! CMR2020 (All versions < V2.2), LOGO! CMR2040 (All versions < V2.2), SIMATIC RTU3010C (All versions < V4.0.9), SIMATIC RTU3030C (All versions < V4.0.9), SIMATIC RTU3031C (All versions < V4.0.9), SIMATIC RTU3041C (All versions < V4.0.9). The underlying TCP/IP stack does not properly calculate the random numbers used as ISN (Initial Sequence Numbers). An adjacent attacker with network access to the LAN interface could interfere with traffic, spoof the connection and gain access to sensitive information.

Frequently asked questions

What is CVE-2021-37186?: A vulnerability has been identified in LOGO! CMR2020 (All versions < V2.2), LOGO! CMR2040 (All versions < V2.2), SIMATIC RTU3010C (All versions < V4.0.9), SIMATIC RTU3030C (All versions < V4.0.9), SIMATIC RTU3031C (All versions < V4.0.9), SIMATIC RTU3041C (All versions < V4.0.9). The underlying TCP/IP stack does not properly calculate the random numbers used as ISN (Initial Sequence Numbers). An adjacent attacker with network access to the LAN interface could interfere with traffic, spoof the connection and gain access to sensitive information.
How severe is CVE-2021-37186?: CVE-2021-37186 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over an adjacent network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2021-37186 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (28th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-37186?: CVE-2021-37186 primarily affects Siemens Logo! Cmr2020 Firmware. In total, 6 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-37186?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-37186 published?: CVE-2021-37186 was published on 2021-09-14 and last updated on 2026-06-17.

References

https://cert-portal.siemens.com/productcert/pdf/ssa-316383.pdf

Affected products (6)

cpe:2.3:o:siemens:logo\!_cmr2020_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:logo\!_cmr2040_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_rtu3010c_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_rtu3030c_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_rtu3031c_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_rtu3041c_firmware:*:*:*:*:*:*:*:*

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