CVE-2021-21166Known exploitationPublic exploitNetwork attack vector

Heap corruption via unlocked Web Audio buffers

Published Mar 9, 2021 · Updated Oct 21, 2025

A data race in Google Chrome before 89.0.4389.72 allows remote attackers to corrupt heap memory through a crafted HTML page. ScriptProcessorNode::process() exposes shared input and output audio buffers to the main and audio-rendering threads without holding its mutex across processing. Activating the page's Web Audio code is required; concurrent sorting causes an out-of-bounds write, and observed exploitation likely chained a sandbox escape.

CVSS severity8.8
High
EPSS probability26.72%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

A data race in Google Chrome before 89.0.4389.72 allows remote attackers to corrupt heap memory through a crafted HTML page. ScriptProcessorNode::process() exposes shared input and output audio buffers to the main and audio-rendering threads without holding its mutex across processing. Activating the page's Web Audio code is required; concurrent sorting causes an out-of-bounds write, and observed exploitation likely chained a sandbox escape.

The record

CVE
CVE-2021-21166
Published
Mar 9, 2021
Updated
Oct 21, 2025
Vendor
Google Cloud
Product
Google Chrome
Classifications
CWE-362, CAPEC-26, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 9, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 3, 2021Exploitation reportedCISA Known Exploited Vulnerabilities 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 <89.0.4389.72

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Google Cloud · Google Chromeversion=unspecified <89.0.4389.72

Published CVSS scores

8.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
8.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:P

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-362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
CAPEC-26Leveraging Race Conditions
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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