CVE-2021-27852Known exploitationNetwork attack vector

Unauthenticated code execution via unchecked _VSTATE deserialization

Published May 27, 2021 · Updated Oct 21, 2025

Deserialization in Checkbox Survey before 7.0 allows remote attackers to execute arbitrary code through a crafted _VSTATE request. CheckboxWeb.dll accepts _VSTATE data and passes it to LosFormatter without enforcing ASP.NET ViewState MAC validation. No authentication or user interaction is required, and execution occurs with web-server privileges on exposed installations.

CVSS severity9.8
Critical
EPSS probability31.95%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Deserialization in Checkbox Survey before 7.0 allows remote attackers to execute arbitrary code through a crafted _VSTATE request. CheckboxWeb.dll accepts _VSTATE data and passes it to LosFormatter without enforcing ASP.NET ViewState MAC validation. No authentication or user interaction is required, and execution occurs with web-server privileges on exposed installations.

The record

CVE
CVE-2021-27852
Published
May 27, 2021
Updated
Oct 21, 2025
Vendor
Checkbox
Product
Checkbox Survey
Classifications
CWE-502, CAPEC-586, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 27, 2021CVE publishedPublication date reported by the CVE source.
  2. Apr 11, 2022Exploitation reportedCISA Known Exploited Vulnerabilities entry for Checkbox Survey
  3. Oct 21, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <7

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Checkbox · Checkbox Surveyversion=unspecified <7

Published CVSS scores

7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P
9.8CERT/CCCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationReported
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-502Deserialization of Untrusted Data
CAPEC-586Object Injection
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Reported exploitation

Technologies

Your stack

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Your stack

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