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Fencer Vulns
medium 6.5

CVE-2021-29945 json

The WebAssembly JIT could miscalculate the size of a return type, which could lead to a null read and result in a crash.

published 2021-06-24 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-16404

cvss
6.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.2%
EPSS 1.2% chance of exploitation in 30 days, percentile 68%
public exploits
0
none known

Summary

The WebAssembly JIT could miscalculate the size of a return type, which could lead to a null read and result in a crash. *Note: This issue only affected x86-32 platforms. Other platforms are unaffected.*. This vulnerability affects Firefox ESR < 78.10, Thunderbird < 78.10, and Firefox < 88.

Patch / fix

  • Mozilla Firefox ESR 78.10
  • Mozilla Thunderbird 78.10
  • Mozilla Firefox 88
  • firefox-esr Debian 14, Debian 13, Debian 12 78.10.0esr-1
  • thunderbird Debian 14, Debian 13, Debian 12 1:78.10.0-1

debian advisories DEBIAN-CVE-2021-29945

  • firefox Ubuntu 16.04 LTS 88.0+build2-0ubuntu0.16.04.1
  • firefox Ubuntu 18.04 LTS 88.0+build2-0ubuntu0.18.04.2
  • firefox Ubuntu 20.04 LTS 88.0+build2-0ubuntu0.20.04.1
  • thunderbird Ubuntu 18.04 LTS 1:78.11.0+build1-0ubuntu0.18.04.2
  • thunderbird Ubuntu 20.04 LTS 1:78.11.0+build1-0ubuntu0.20.04.2

ubuntu advisories UBUNTU-CVE-2021-29945

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 RHEL 7 78.10.0-1.el7_9
  • firefox RHEL 8 78.10.0-1.el8_3
  • thunderbird RHEL 8 78.10.0-1.el8_3
  • thunderbird RHEL 7 78.10.0-1.el7_9
  • firefox RHEL 8.1 EUS 78.10.0-1.el8_1
  • firefox RHEL 8.2 EUS 78.10.0-1.el8_2
  • thunderbird RHEL 8.1 EUS 78.10.0-1.el8_1
  • thunderbird RHEL 8.2 EUS 78.10.0-1.el8_2

red hat advisories RHSA-2021:1363RHSA-2021:1362RHSA-2021:1360RHSA-2021:1361RHSA-2021:1351RHSA-2021:1353

  • MozillaFirefox SLES for SAP 15 SP1, SLES for SAP 15, SLES 15-LTSS +10 more 78.10.0-3.139.1
  • MozillaThunderbird SLE Workstation Extension 15 SP2 78.10.0-8.23.1
  • MozillaFirefox SLES for SAP 12 SP5, SLES for SAP 12 SP4, SLES for SAP 12 SP3 +11 more 78.10.0-112.57.2
  • MozillaFirefox SLE Module for Desktop Applications 15 SP2 78.10.0-8.38.1
  • MozillaFirefox SLES 11 SP4-LTSS 78.10.0-78.126.1

suse advisories SUSE-SU-2021:1433-1SUSE-SU-2021:1432-1SUSE-SU-2021:14708-1SUSE-SU-2021:1325-1SUSE-SU-2021:1307-1

  • firefox-esr openSUSE Tumbleweed 128.5.1-1.1
  • MozillaFirefox openSUSE Tumbleweed 92.0-1.2
  • MozillaThunderbird openSUSE Tumbleweed 91.1.1-1.1
  • MozillaThunderbird openSUSE Leap 15.2 78.10.0-lp152.2.41.1
  • MozillaFirefox openSUSE Leap 15.2 78.10.0-lp152.2.55.1

opensuse advisories openSUSE-SU-2024:14572-1openSUSE-SU-2024:10600-1openSUSE-SU-2024:10601-1openSUSE-SU-2021:0644-1openSUSE-SU-2021:0621-1

  • firefox Alpine 3.23, Alpine 3.22, Alpine 3.21 +8 more 88.0-r0
  • mozjs78 Alpine 3.16, Alpine 3.15, Alpine 3.14 +1 more 78.10.0-r0
  • librewolf Alpine 3.24, Alpine 3.23, Alpine 3.22 +1 more 88.0-r0
  • firefox-esr Alpine 3.23, Alpine 3.22, Alpine 3.21 +9 more 78.10.0-r0
  • thunderbird Alpine 3.23, Alpine 3.22, Alpine 3.21 +5 more 91.3.2-r0

alpine advisories ALPINE-CVE-2021-29945

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

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-2021-29945 updated cvss 6.1

Mozilla: Incorrect size computation in WebAssembly JIT could lead to null-reads

  • Red Hat Enterprise Linux 6 firefox, thunderbird
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux AppStream (v. 8) firefox 78.10.0-1.el8_3, thunderbird 78.10.0-1.el8_3
    fixed: vendor fix RHSA-2021:1360
  • Red Hat Enterprise Linux AppStream EUS (v. 8.1) firefox 78.10.0-1.el8_1, thunderbird 78.10.0-1.el8_1
    fixed: vendor fix RHSA-2021:1362
  • Red Hat Enterprise Linux AppStream EUS (v. 8.2) firefox 78.10.0-1.el8_2, thunderbird 78.10.0-1.el8_2
    fixed: vendor fix RHSA-2021:1361
  • Red Hat Enterprise Linux Client (v. 7) firefox 78.10.0-1.el7_9, thunderbird 78.10.0-1.el7_9 Red Hat Enterprise Linux Client Optional (v. 7) firefox 78.10.0-1.el7_9 Red Hat Enterprise Linux Server (v. 7) firefox 78.10.0-1.el7_9 Red Hat Enterprise Linux Server Optional (v. 7) firefox 78.10.0-1.el7_9, thunderbird 78.10.0-1.el7_9 Red Hat Enterprise Linux Workstation (v. 7) firefox 78.10.0-1.el7_9, thunderbird 78.10.0-1.el7_9 Red Hat Enterprise Linux Workstation Optional (v. 7) firefox 78.10.0-1.el7_9
    fixed: vendor fix RHSA-2021:1363

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

1.20% chance of exploitation in the next 30 days, higher than 68% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
NVD 2.0 4.3 AV:N/AC:M/Au:N/C:N/I:N/A:P

Affected products

  • Mozilla Firefox ESR
  • Mozilla Thunderbird
  • Mozilla Firefox

Classification

Weakness

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.