What is CVE-2021-31340?

A vulnerability has been identified in SIMATIC RF166C (All versions > V1.1 and V1.1 and V1.1 and V1.1 and V1.1 and V1.1 and V3.0 V3.0 V3.0 V3.0 V3.0 V3.0 V3.0 V3.0 V3.0 V3.0 V3.0 V3.0 V3.0 V3.0 V3.0 V3.0 V3.0 V3.0 < V4.0). Affected devices do not properly handle large numbers of incoming connections. An attacker may leverage this to cause a Denial-of-Service situation.

How severe is CVE-2021-31340?

CVE-2021-31340 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-31340 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (58th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-31340?

CVE-2021-31340 primarily affects Siemens Simatic Rf166c Firmware. In total, 25 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-31340?

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

When was CVE-2021-31340 published?

CVE-2021-31340 was published on 2021-06-08 and last updated on 2026-06-17.

CVE-2021-31340

Q: How severe is CVE-2021-31340?

CVE-2021-31340 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Q: Is CVE-2021-31340 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (58th percentile), an estimate of the probability of exploitation in the next 30 days.

Q: What products are affected by CVE-2021-31340?

CVE-2021-31340 primarily affects Siemens Simatic Rf166c Firmware. In total, 25 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

Q: How do I fix CVE-2021-31340?

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

Q: When was CVE-2021-31340 published?

CVE-2021-31340 was published on 2021-06-08 and last updated on 2026-06-17.

CVE-2021-31340 is a high-severity vulnerability in Siemens Simatic Rf166c Firmware with a CVSS 3.x base score of 7.5. 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-400.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 1% (58th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-400
Affected product: Siemens Simatic Rf166c Firmware
Published: 2021-06-08
Last modified: 2026-06-17

Description

A vulnerability has been identified in SIMATIC RF166C (All versions > V1.1 and < V1.3.2), SIMATIC RF185C (All versions > V1.1 and < V1.3.2), SIMATIC RF186C (All versions > V1.1 and < V1.3.2), SIMATIC RF186CI (All versions > V1.1 and < V1.3.2), SIMATIC RF188C (All versions > V1.1 and < V1.3.2), SIMATIC RF188CI (All versions > V1.1 and < V1.3.2), SIMATIC RF360R (All versions < V2.0), SIMATIC Reader RF610R CMIIT (All versions > V3.0 < V4.0), SIMATIC Reader RF610R ETSI (All versions > V3.0 < V4.0), SIMATIC Reader RF610R FCC (All versions > V3.0 < V4.0), SIMATIC Reader RF615R CMIIT (All versions > V3.0 < V4.0), SIMATIC Reader RF615R ETSI (All versions > V3.0 < V4.0), SIMATIC Reader RF615R FCC (All versions > V3.0 < V4.0), SIMATIC Reader RF650R ARIB (All versions > V3.0 < V4.0), SIMATIC Reader RF650R CMIIT (All versions > V3.0 < V4.0), SIMATIC Reader RF650R ETSI (All versions > V3.0 < V4.0), SIMATIC Reader RF650R FCC (All versions > V3.0 < V4.0), SIMATIC Reader RF680R ARIB (All versions > V3.0 < V4.0), SIMATIC Reader RF680R CMIIT (All versions > V3.0 < V4.0), SIMATIC Reader RF680R ETSI (All versions > V3.0 < V4.0), SIMATIC Reader RF680R FCC (All versions > V3.0 < V4.0), SIMATIC Reader RF685R ARIB (All versions > V3.0 < V4.0), SIMATIC Reader RF685R CMIIT (All versions > V3.0 < V4.0), SIMATIC Reader RF685R ETSI (All versions > V3.0 < V4.0), SIMATIC Reader RF685R FCC (All versions > V3.0 < V4.0). Affected devices do not properly handle large numbers of incoming connections. An attacker may leverage this to cause a Denial-of-Service situation.

Frequently asked questions

What is CVE-2021-31340?: A vulnerability has been identified in SIMATIC RF166C (All versions > V1.1 and < V1.3.2), SIMATIC RF185C (All versions > V1.1 and < V1.3.2), SIMATIC RF186C (All versions > V1.1 and < V1.3.2), SIMATIC RF186CI (All versions > V1.1 and < V1.3.2), SIMATIC RF188C (All versions > V1.1 and < V1.3.2), SIMATIC RF188CI (All versions > V1.1 and < V1.3.2), SIMATIC RF360R (All versions < V2.0), SIMATIC Reader RF610R CMIIT (All versions > V3.0 < V4.0), SIMATIC Reader RF610R ETSI (All versions > V3.0 < V4.0), SIMATIC Reader RF610R FCC (All versions > V3.0 < V4.0), SIMATIC Reader RF615R CMIIT (All versions > V3.0 < V4.0), SIMATIC Reader RF615R ETSI (All versions > V3.0 < V4.0), SIMATIC Reader RF615R FCC (All versions > V3.0 < V4.0), SIMATIC Reader RF650R ARIB (All versions > V3.0 < V4.0), SIMATIC Reader RF650R CMIIT (All versions > V3.0 < V4.0), SIMATIC Reader RF650R ETSI (All versions > V3.0 < V4.0), SIMATIC Reader RF650R FCC (All versions > V3.0 < V4.0), SIMATIC Reader RF680R ARIB (All versions > V3.0 < V4.0), SIMATIC Reader RF680R CMIIT (All versions > V3.0 < V4.0), SIMATIC Reader RF680R ETSI (All versions > V3.0 < V4.0), SIMATIC Reader RF680R FCC (All versions > V3.0 < V4.0), SIMATIC Reader RF685R ARIB (All versions > V3.0 < V4.0), SIMATIC Reader RF685R CMIIT (All versions > V3.0 < V4.0), SIMATIC Reader RF685R ETSI (All versions > V3.0 < V4.0), SIMATIC Reader RF685R FCC (All versions > V3.0 < V4.0). Affected devices do not properly handle large numbers of incoming connections. An attacker may leverage this to cause a Denial-of-Service situation.
How severe is CVE-2021-31340?: CVE-2021-31340 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-31340 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (58th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-31340?: CVE-2021-31340 primarily affects Siemens Simatic Rf166c Firmware. In total, 25 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-31340?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-31340 published?: CVE-2021-31340 was published on 2021-06-08 and last updated on 2026-06-17.

References

https://cert-portal.siemens.com/productcert/pdf/ssa-787292.pdf

Affected products (25)

cpe:2.3:o:siemens:simatic_rf166c_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_rf185c_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_rf186c_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_rf186ci_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_rf188c_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_rf188ci_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_rf360r_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_reader_rf610r_cmiit_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_reader_rf610r_etsi_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_reader_rf610r_fcc_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_reader_rf615r_cmiit_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_reader_rf615r_etsi_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_reader_rf615r_fcc_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_reader_rf650r_cmiit_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_reader_rf650r_etsi_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_reader_rf650r_fcc_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_reader_rf650r_arib_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_reader_rf680r_cmiit_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_reader_rf680r_etsi_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_reader_rf680r_fcc_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_reader_rf680r_arib_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_reader_rf685r_cmiit_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_reader_rf685r_etsi_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_reader_rf685r_fcc_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_reader_rf685r_arib_firmware:*:*:*:*:*:*:*:*

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