CVE-2021-29952Network attack vector

Arbitrary code execution via WebRender teardown race

Published Jun 24, 2021 · Updated Aug 3, 2024

Race condition in Mozilla Firefox before 88.0.1 and Firefox for Android before 88.1.3 allows remote attackers to execute arbitrary code. WebRenderBridgeParent::ClearResources destroys resources on the compositor thread while a scene-builder thread can still access the associated compositor and WebRender data structures. A victim must interact with attacker-controlled network content, and exploitation requires winning a difficult shutdown or window-close race that can instead crash the browser.

CVSS severity7.5
High
EPSS probability0.73%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Race condition in Mozilla Firefox before 88.0.1 and Firefox for Android before 88.1.3 allows remote attackers to execute arbitrary code. WebRenderBridgeParent::ClearResources destroys resources on the compositor thread while a scene-builder thread can still access the associated compositor and WebRender data structures. A victim must interact with attacker-controlled network content, and exploitation requires winning a difficult shutdown or window-close race that can instead crash the browser.

The record

CVE
CVE-2021-29952
Published
Jun 24, 2021
Updated
Aug 3, 2024
Vendor
Mozilla
Product
Firefox
Classifications
CWE-362, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 24, 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 <88.0.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <88.0.1
Mozilla · Firefox for Androidversion=unspecified <88.1.3

Published CVSS scores

5.1NIST NVDAV:N/AC:H/Au:N/C:P/I:P/A:P
7.5NIST NVDCVSS:3.1/AV:N/AC:H/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 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-362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
T1203Exploitation for Client Execution

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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