How severe is CVE-2021-27661?

CVE-2021-27661 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-27661 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (53rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-27661?

CVE-2021-27661 affects Johnsoncontrols F4-snc Firmware. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-27661?

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-2021-27661 published?

CVE-2021-27661 was published on 2021-07-01 and last updated on 2026-06-17.

CVE-2021-27661

CVE-2021-27661 is a high-severity vulnerability in Johnsoncontrols F4-snc Firmware with a CVSS 3.x base score of 8.8. 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-863.

Key facts

Severity: High (CVSS 3.x base score 8.8)
CVSS v2: 6.5
EPSS exploit prediction: 1% (53rd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-863
Affected product: Johnsoncontrols F4-snc Firmware
Published: 2021-07-01
Last modified: 2026-06-17

Description

Successful exploitation of this vulnerability could give an authenticated Facility Explorer SNC Series Supervisory Controller (F4-SNC) user an unintended level of access to the controller’s file system, allowing them to access or modify system files by sending specifically crafted web messages to the F4-SNC.

Frequently asked questions

What is CVE-2021-27661?: Successful exploitation of this vulnerability could give an authenticated Facility Explorer SNC Series Supervisory Controller (F4-SNC) user an unintended level of access to the controller’s file system, allowing them to access or modify system files by sending specifically crafted web messages to the F4-SNC.
How severe is CVE-2021-27661?: CVE-2021-27661 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-27661 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (53rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-27661?: CVE-2021-27661 affects Johnsoncontrols F4-snc Firmware. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-27661?: 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-2021-27661 published?: CVE-2021-27661 was published on 2021-07-01 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:o:johnsoncontrols:f4-snc_firmware:11:*:*:*:*:*:*:*

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