CVE-2021-21220Known exploitationPublic exploitNetwork attack vector

Remote code execution via JIT sign-extension error

Published Apr 26, 2021 · Updated Oct 21, 2025

Improper input validation in V8 in Google Chrome before 89.0.4389.128 allows remote attackers to execute code via crafted HTML. V8's x64 optimizer removes a no-op XOR without preserving its signed result type, causing VisitChangeInt32ToInt64 to zero-extend an unsigned value instead of sign-extending it. A victim must load attacker-controlled HTML on an x86_64 build; the demonstrated primitive executes code in the renderer, without a documented sandbox escape.

CVSS severity8.8
High
EPSS probability70.44%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in V8 in Google Chrome before 89.0.4389.128 allows remote attackers to execute code via crafted HTML. V8's x64 optimizer removes a no-op XOR without preserving its signed result type, causing VisitChangeInt32ToInt64 to zero-extend an unsigned value instead of sign-extending it. A victim must load attacker-controlled HTML on an x86_64 build; the demonstrated primitive executes code in the renderer, without a documented sandbox escape.

The record

CVE
CVE-2021-21220
Published
Apr 26, 2021
Updated
Oct 21, 2025
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. Nov 3, 2021Exploitation reportedCISA Known Exploited Vulnerabilities catalog listing
  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 <89.0.4389.128

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Google Cloud · Google Chromeversion=unspecified <89.0.4389.128

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 exploitationReported
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.

Reported exploitation

Technologies

Your stack

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Your stack

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