CVE-2021-21225Public exploitNetwork attack vector

Renderer code execution via stale concat length

Published Apr 26, 2021 · Updated Aug 3, 2024

Out-of-bounds memory access in V8 in Google Chrome before 90.0.4430.85 allows remote attackers to corrupt heap memory via crafted HTML. Array.prototype.concat retains an array's original fast length after a callback shortens its elements store, so iteration reads beyond the new boundary. A user must load attacker-controlled content; successful exploitation executes code in the renderer process, which remains constrained by the Chrome sandbox unless chained with another flaw.

CVSS severity8.8
High
EPSS probability6.63%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds memory access in V8 in Google Chrome before 90.0.4430.85 allows remote attackers to corrupt heap memory via crafted HTML. Array.prototype.concat retains an array's original fast length after a callback shortens its elements store, so iteration reads beyond the new boundary. A user must load attacker-controlled content; successful exploitation executes code in the renderer process, which remains constrained by the Chrome sandbox unless chained with another flaw.

The record

CVE
CVE-2021-21225
Published
Apr 26, 2021
Updated
Aug 3, 2024
Vendor
Google Cloud
Product
Google Chrome
Classifications
CWE-787, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 26, 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 <90.0.4430.85

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Google Cloud · Google Chromeversion=unspecified <90.0.4430.85

Published CVSS scores

6.8NVDAV:N/AC:M/Au:N/C:P/I:P/A:P
8.8NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/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 exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1203Exploitation for Client Execution

Public exploit references

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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