CVE-2021-37186

Severity: medium (CVSS 5.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-09-14 · updated 2026-06-17
Weakness: CWE-330

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.

Affected products

Siemens Logo! Cmr2020 Firmware: before 2.2 — fixed in 2.2
Siemens Logo! Cmr2040 Firmware: before 2.2 — fixed in 2.2
Siemens Simatic Rtu3010C Firmware: before 4.0.9 — fixed in 4.0.9
Siemens Simatic Rtu3030C Firmware: before 4.0.9 — fixed in 4.0.9
Siemens Simatic Rtu3031C Firmware: before 4.0.9 — fixed in 4.0.9
Siemens Simatic Rtu3041C Firmware: before 4.0.9 — fixed in 4.0.9

How to fix

Upgrade to a fixed version: Siemens Logo! Cmr2020 Firmware 2.2; Siemens Logo! Cmr2040 Firmware 2.2; Siemens Simatic Rtu3010C Firmware 4.0.9; Siemens Simatic Rtu3030C Firmware 4.0.9; Siemens Simatic Rtu3031C Firmware 4.0.9; Siemens Simatic Rtu3041C Firmware 4.0.9. Check the vendor advisory for mitigations.

References

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