CVE-2021-27852: in the CISA KEV catalogue

Checkbox Survey Deserialization of Untrusted Data Vulnerability. CISA added CVE-2021-27852 to the Known Exploited Vulnerabilities catalogue on 2022-04-11 with a default due date of 2022-05-02. Known ransomware campaign use: Unknown. Forensic triage flag: No.

Deserialization of Untrusted Data vulnerability in CheckboxWeb.dll of Checkbox Survey allows an unauthenticated remote attacker to execute arbitrary code. (CISA description)

Vendor / product: Checkbox Checkbox Survey
CWE: CWE-502
CISA required action: Versions 6 and earlier for this product are end-of-life and must be removed from agency networks. Versions 7 and later are not considered vulnerable.
EPSS: 30%, percentile 98 (scored 2026-11-03)

EPSS puts about 30 in 100 odds (30%) on exploitation activity being observed in the next 30 days. Its score is higher than or equal to that of 98% of scored CVEs. This is a model estimate about exploitation anywhere, not about your environment.

Vendor and reference links (from CISA)

https://nvd.nist.gov/vuln/detail/CVE-2021-27852

Your own deadline under CISA BOD 26-04 depends on exposure, automatability and technical impact: work it out with the BOD 26-04 calculator.

Data dates. CISA KEV catalogue version 2026.11.03, released 2026-11-03, 1,767 entries (checked 2026-11-03). EPSS model v2026.06.15, scored 2026-11-03, 399,388 CVEs. Sources: CISA and FIRST (EPSS by FIRST; scores generated by Empirical Security). Copied to our own database and refreshed automatically; if a refresh fails, the previous copy keeps serving with its own date.

Frequently asked questions

Is CVE-2021-27852 in the CISA KEV catalogue?

Yes. CISA added CVE-2021-27852 (Checkbox Survey Deserialization of Untrusted Data Vulnerability) to the Known Exploited Vulnerabilities catalogue on 2022-04-11. CISA's default due date for it is 2022-05-02.

Is CVE-2021-27852 used in ransomware attacks?

CISA marks known ransomware campaign use as Unknown for CVE-2021-27852. That means CISA lacks confirmation, not that ransomware groups do not use it.

What should I do about CVE-2021-27852?

CISA's required action: Versions 6 and earlier for this product are end-of-life and must be removed from agency networks. Versions 7 and later are not considered vulnerable.

Sources

CISA, Known Exploited Vulnerabilities Catalog (accessed 2026-11-03)
FIRST, Exploit Prediction Scoring System (EPSS) (EPSS by FIRST; scores generated by Empirical Security)
NVD record for CVE-2021-27852