CVE-2021-21139Network attack vector

Navigation restriction bypass via iframe sandbox enforcement

Published Feb 9, 2021 · Updated Aug 3, 2024

Improper iframe sandbox enforcement in Google Chrome before 88.0.4324.96 allows remote attackers to bypass navigation restrictions. Google has not disclosed the code-level locus or the specific sandbox check that mishandles the crafted HTML page. Exploitation requires a user to load attacker-controlled HTML; the documented consequence is unauthorized navigation, not data disclosure or service interruption.

CVSS severity6.5
Medium
EPSS probability4.74%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper iframe sandbox enforcement in Google Chrome before 88.0.4324.96 allows remote attackers to bypass navigation restrictions. Google has not disclosed the code-level locus or the specific sandbox check that mishandles the crafted HTML page. Exploitation requires a user to load attacker-controlled HTML; the documented consequence is unauthorized navigation, not data disclosure or service interruption.

The record

CVE
CVE-2021-21139
Published
Feb 9, 2021
Updated
Aug 3, 2024
Vendor
Google Cloud
Product
Google Chrome
Classifications
CWE-1021
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 9, 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 <88.0.4324.96

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Google Cloud · Google Chromeversion=unspecified <88.0.4324.96

Published CVSS scores

4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

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 exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-1021Improper Restriction of Rendered UI Layers or Frames

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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