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.

Published: 2021-09-14 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-37186 is rated Low Risk (30.9/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.34%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-37186

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.17% 0.34% +0.18%
2 2025-11-21 0.07% 0.17% +0.09%
3 2025-11-18 — 0.07% —

Full EPSS history (12 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-37186

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.4 3.1 MEDIUM
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N Click to expand
Attack vector (AV:A)
Attacker has to be nearby on the network—same office, same link, that vibe—not the whole wide internet.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 2.8 2.5 [email protected]
4.8 2.0 MEDIUM
AV:A/AC:L/Au:N/C:P/I:P/A:N Click to expand
Access vector (AV:A)
Requires access to an adjacent network segment.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:N)
No availability impact.
 6.5 4.9 [email protected]

Weakness enumeration for CVE-2021-37186

Affected software / configurations for CVE-2021-37186

Vendor Product Version Raw CPE
siemens logo\!_cmr2020_firmware < 2.2 cpe:2.3:o:siemens:logo\!_cmr2020_firmware:*:*:*:*:*:*:*:*
siemens logo\!_cmr2040_firmware < 2.2 cpe:2.3:o:siemens:logo\!_cmr2040_firmware:*:*:*:*:*:*:*:*
siemens simatic_rtu3010c_firmware < 4.0.9 cpe:2.3:o:siemens:simatic_rtu3010c_firmware:*:*:*:*:*:*:*:*
siemens simatic_rtu3030c_firmware < 4.0.9 cpe:2.3:o:siemens:simatic_rtu3030c_firmware:*:*:*:*:*:*:*:*
siemens simatic_rtu3031c_firmware < 4.0.9 cpe:2.3:o:siemens:simatic_rtu3031c_firmware:*:*:*:*:*:*:*:*
siemens simatic_rtu3041c_firmware < 4.0.9 cpe:2.3:o:siemens:simatic_rtu3041c_firmware:*:*:*:*:*:*:*:*

References for CVE-2021-37186

cvelogic Threat Intelligence