CVE-2021-27852: Checkbox Survey Deserialization of Untrusted Data Vulnerability

CVE-2021-27852 is a deserialization of untrusted data flaw in Checkbox Survey, specifically within CheckboxWeb.dll. An unauthenticated remote attacker can abuse it to execute arbitrary code on the host. That makes the issue high impact for any organization still running the product, because successful exploitation can lead directly to full system compromise without needing valid credentials.

CISA notes that versions 6 and earlier are end-of-life and must be removed from agency networks; versions 7 and later are not considered vulnerable. Confirm exact status against the vendor advisory before acting.

How it works

The weakness is CWE-502: Deserialization of Untrusted Data. Checkbox Survey accepts serialized objects (via CheckboxWeb.dll) and reconstructs them in memory without adequate validation of their origin or content. An attacker who can supply a crafted serialized payload can cause the application to instantiate unexpected object types or invoke dangerous methods during the deserialization process. Because the attack requires no authentication, any network-reachable instance of the vulnerable component is a potential target. Exact request format and payload construction are not detailed in the public summary; treat any unauthenticated input path that reaches the deserialization logic as suspect and verify behavior against the vendor advisory.

Am I affected? How to find it in your systems

Checkbox Survey is typically deployed as a web application on Windows servers, often in environments that collect internal or external survey data. Inventory steps:

• Search software inventories, CMDB records, and package lists for “Checkbox Survey” or the presence of CheckboxWeb.dll.
• Examine web-server document roots, IIS application pools, and installed-program lists on hosts that serve survey or form-collection workloads.
• Identify any instances running version 6 or earlier; those releases are end-of-life and explicitly called out by CISA as requiring removal. Versions 7 and later are stated to be not vulnerable—confirm the precise build you are running against the vendor advisory.
• Review web-access logs for anomalous unauthenticated POSTs or other requests that target survey-related endpoints and carry large or unusual binary/serialized payloads. Sudden process creation, unexpected child processes spawned by the survey application pool, or outbound connections from the survey host can also indicate exploitation attempts.

How to remediate

Primary action is to eliminate the vulnerable code:

• For versions 6 and earlier, remove the product from the network entirely; these releases are end-of-life and no longer receive security fixes.
• For any remaining installations, upgrade to a version 7 or later release that the vendor and CISA consider non-vulnerable. Obtain the update directly from the vendor and follow their installation guidance.
• After remediation, re-scan the host to confirm CheckboxWeb.dll from the old version is gone and that the application is no longer listening on previously exposed ports or virtual directories.
• As general hardening for deserialization flaws, ensure the application runs under a least-privilege service account, disable any unused serialization formatters, and keep the underlying OS and web-server stack fully patched.

If you can't patch immediately

If immediate removal or upgrade is not possible, apply compensating controls to shrink the attack surface:

• Segment the host so that only explicitly authorized management and application networks can reach the survey service; block all other inbound traffic at the firewall or network ACL.
• Place a web application firewall or reverse-proxy rule in front of the service to drop requests that contain serialized object markers or unusually large binary bodies destined for survey endpoints.
• Disable or restrict any public-facing survey features that are not strictly required; if the application can be taken offline temporarily, do so.
• Increase monitoring: alert on new process creation by the survey worker process, on unexpected outbound connections, and on web-log patterns that match unauthenticated access to deserialization entry points. Retain these logs for forensic review.

If your data may have been exposed

Actively exploited remote-code-execution vulnerabilities frequently precede broader network compromise and data theft. If you discover evidence of exploitation or cannot rule it out, treat the host as potentially breached: isolate it, preserve volatile evidence, and begin incident-response procedures. As a quick additional check, you can run a free exposure scan of your email addresses against known breach data sets to see whether credentials or personal information have already appeared in public dumps.