CVE-2021-21111Network attack vector

Sandbox escape via WebUI policy enforcement failure

Published Jan 8, 2021 · Updated Aug 3, 2024

Insufficient policy enforcement in Google Chrome WebUI before 87.0.4280.141 allows attackers to escape the browser sandbox via a crafted extension. Google identifies WebUI as the locus, but the restricted bug record leaves the failed policy check and crafted-extension trigger undisclosed. Exploitation requires persuading a user to install the malicious extension; public sources do not identify the resources reachable after escape.

CVSS severity9.6
Critical
EPSS probability1.06%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Insufficient policy enforcement in Google Chrome WebUI before 87.0.4280.141 allows attackers to escape the browser sandbox via a crafted extension. Google identifies WebUI as the locus, but the restricted bug record leaves the failed policy check and crafted-extension trigger undisclosed. Exploitation requires persuading a user to install the malicious extension; public sources do not identify the resources reachable after escape.

The record

CVE
CVE-2021-21111
Published
Jan 8, 2021
Updated
Aug 3, 2024
Vendor
Google Cloud
Product
Google Chrome
Classifications
CWE-1021, T1068
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 8, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record 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 <87.0.4280.141

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Google Cloud · Google Chromeversion=unspecified <87.0.4280.141

Published CVSS scores

6.8NIST National Vulnerability DatabaseAV:N/AC:M/Au:N/C:P/I:P/A:P
9.6NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-1021Improper Restriction of Rendered UI Layers or Frames
T1068Exploitation for Privilege Escalation

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.

Technologies

Your stack

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Your stack

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