How severe is CVE-2021-27395?

CVE-2021-27395 has a CVSS 3.x base score of 8.1, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability high.

Is CVE-2021-27395 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (51st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-27395?

CVE-2021-27395 primarily affects Siemens Simatic Process Historian 2013. In total, 7 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-27395?

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-2021-27395 published?

CVE-2021-27395 was published on 2021-10-12 and last updated on 2026-06-17.

CVE-2021-27395

CVE-2021-27395 is a high-severity vulnerability in Siemens Simatic Process Historian 2013 with a CVSS 3.x base score of 8.1. 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: High (CVSS 3.x base score 8.1)
CVSS v2: 5.5
EPSS exploit prediction: 1% (51st percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-306
Affected product: Siemens Simatic Process Historian 2013
Published: 2021-10-12
Last modified: 2026-06-17

Description

A vulnerability has been identified in SIMATIC Process Historian 2013 and earlier (All versions), SIMATIC Process Historian 2014 (All versions < SP3 Update 6), SIMATIC Process Historian 2019 (All versions), SIMATIC Process Historian 2020 (All versions). An interface in the software that is used for critical functionalities lacks authentication, which could allow a malicious user to maliciously insert, modify or delete data.

Frequently asked questions

What is CVE-2021-27395?: A vulnerability has been identified in SIMATIC Process Historian 2013 and earlier (All versions), SIMATIC Process Historian 2014 (All versions < SP3 Update 6), SIMATIC Process Historian 2019 (All versions), SIMATIC Process Historian 2020 (All versions). An interface in the software that is used for critical functionalities lacks authentication, which could allow a malicious user to maliciously insert, modify or delete data.
How severe is CVE-2021-27395?: CVE-2021-27395 has a CVSS 3.x base score of 8.1, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability high.
Is CVE-2021-27395 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (51st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-27395?: CVE-2021-27395 primarily affects Siemens Simatic Process Historian 2013. In total, 7 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-27395?: 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-2021-27395 published?: CVE-2021-27395 was published on 2021-10-12 and last updated on 2026-06-17.

References

https://cert-portal.siemens.com/productcert/pdf/ssa-766247.pdf

Affected products (7)

cpe:2.3:a:siemens:simatic_process_historian_2013:*:*:*:*:*:*:*:*
cpe:2.3:a:siemens:simatic_process_historian_2014:-:sp1:*:*:*:*:*:*
cpe:2.3:a:siemens:simatic_process_historian_2014:-:sp2:*:*:*:*:*:*
cpe:2.3:a:siemens:simatic_process_historian_2014:-:sp3:*:*:*:*:*:*
cpe:2.3:a:siemens:simatic_process_historian_2014:-:sp3_update4:*:*:*:*:*:*
cpe:2.3:a:siemens:simatic_process_historian_2019:*:*:*:*:*:*:*:*
cpe:2.3:a:siemens:simatic_process_historian_2020:*:*:*:*:*:*:*:*

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