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Fencer Vulns
high 7.5

CVE-2021-29952 json

When Web Render components were destructed, a race condition could have caused undefined behavior, and we presume that with enough effort m…

published 2021-06-24 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-16411

cvss
7.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.7%
EPSS 0.7% chance of exploitation in 30 days, percentile 54%
public exploits
0
none known

Summary

When Web Render components were destructed, a race condition could have caused undefined behavior, and we presume that with enough effort may have been exploitable to run arbitrary code. This vulnerability affects Firefox < 88.0.1 and Firefox for Android < 88.1.3.

Patch / fix

  • Mozilla Firefox 88.0.1
  • Mozilla Firefox for Android 88.1.3
  • firefox Ubuntu 18.04 LTS 88.0.1+build1-0ubuntu0.18.04.2
  • firefox Ubuntu 20.04 LTS 88.0.1+build1-0ubuntu0.20.04.2

ubuntu advisories UBUNTU-CVE-2021-29952

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • firefox-esr openSUSE Tumbleweed 128.5.1-1.1
  • MozillaFirefox openSUSE Tumbleweed 92.0-1.2

opensuse advisories openSUSE-SU-2024:14572-1openSUSE-SU-2024:10600-1

  • firefox Alpine 3.23, Alpine 3.22, Alpine 3.21 +8 more 88.0.1-r0
  • librewolf Alpine 3.24, Alpine 3.23, Alpine 3.22 +1 more 88.0.1-r0

alpine advisories ALPINE-CVE-2021-29952

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • firefox Arch Linux 88.0.1-1

arch linux advisories AVG-1917

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-29952 updated cvss 7.5

Mozilla: Race condition in Web Render Components

  • Red Hat Enterprise Linux 6 firefox Red Hat Enterprise Linux 7 firefox Red Hat Enterprise Linux 8 firefox
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.74% chance of exploitation in the next 30 days, higher than 54% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
NVD 2.0 5.1 AV:N/AC:H/Au:N/C:P/I:P/A:P

Affected products

  • Mozilla Firefox
  • Mozilla Firefox for Android

Classification

Weakness
  • CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.