Exploited. On CISA's list since 2022-04-11.

Checkbox Survey Deserialization of Untrusted Data Vulnerability

CVE-2021-27852 · Checkbox Checkbox Survey · Published 2021-05-27

How bad would it be?

9.8 out of 10

CVSS rates it critical: about as damaging as flaws get.

How likely is it to be used?

30%

Estimated chance of exploitation in the next 30 days, higher than 98% of all scored flaws (EPSS, 2026-10-29).

Is it already being used?

Yes

CISA has seen it exploited in real attacks. For US government agencies the fix is deadline passed 1642 days ago (2022-05-02).

What CISA says to do

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.

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

nvd.nist.gov

What the flaw is

Deserialization of Untrusted Data vulnerability in CheckboxWeb.dll of Checkbox Survey allows an unauthenticated remote attacker to execute arbitrary code. This issue affects: Checkbox Survey versions prior to 7.

From the NVD.

Learn this

Explore this week’s weaknesses and all learning topics

Understand the kind of weakness behind this flaw. These resources teach the weakness, rather than reproduce this specific CVE. Follow the vendor's advice above to fix the affected product.

Insecure deserialization

Rebuilding objects from untrusted saved data can trigger unintended behaviour.

CWE-502 · CISA KEV; NVD record: 134c704f-9b21-4f2e-91b3-4a467353bcc0; NVD record: nvd@nist.gov

Reading and practice labs · Free account for labs. Basic HTTP knowledge; some labs use Burp Suite.

Explore the labs at PortSwigger Web Security Academy How it is prevented

CWE is a catalogue of weakness types. Labels come from the sources shown and can differ or change. Resource matches reviewed 16 October 2026.

On SentryFeed

No story in the last 14 days has mentioned it.

Exploited flaws from CISA's KEV catalogue. Chance of exploitation from EPSS by FIRST. Descriptions and scores from the NVD. This product uses the NVD API but is not endorsed or certified by the NVD.