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TI-2021-10593 Aliases CVE-2021-29976GHSA-jv3x-w8ff-cj2g

Out-of-bounds write in Mozilla Thunderbird

Priority MEDIUM 41CWE-787Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
Required
Attack complexity
Low
Impact type
Code execution
Confidentiality · integrity · availability
High · High · High
Fix status
Partial Red Hat: 9 fixed, 1 without a fix

Attack profile from CVSS 3.1 · NVD. Fix status from CNA and Red Hat. Impact type from CWE-787 and the CVSS impact.

Summary

Mozilla developers reported memory safety bugs present in code shared between Firefox and Thunderbird. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Thunderbird < 78.12, Firefox ESR < 78.12, and Firefox < 90.

Why it matters now

EPSS 0.01223 68th percentileScored 2026-11-07
Fix Partial Thunderbird (Mozilla): 78.12Firefox ESR (Mozilla): 78.12+1 more productRed Hat: 8 advisoriesRed Hat: 9 fixed, 1 without a fix

SSVC decision points

Not available: CISA has not published SSVC decision points for this record.

Affected products

VendorProductAffected versionsFixed inStatusSource
MozillaThunderbirdbefore 78.1278.12Patch availableCNA
MozillaFirefox ESRbefore 78.1278.12Patch availableCNA
MozillaFirefoxbefore 9090Patch availableCNA
  • Thunderbird VendorMozilla Affected before 78.12 Fixed in 78.12 Patch available CNA
  • Firefox ESR VendorMozilla Affected before 78.12 Fixed in 78.12 Patch available CNA
  • Firefox VendorMozilla Affected before 90 Fixed in 90 Patch available CNA

CPE configurations NVD · 3

CPEVersionsRoleVendor
cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*before 90.0VulnerableMozilla
cpe:2.3:a:mozilla:firefox_esr:*:*:*:*:*:*:*:*before 78.12VulnerableMozilla
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*before 78.12VulnerableMozilla
  • cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:* Versions before 90.0 Vulnerable ·Mozilla
  • cpe:2.3:a:mozilla:firefox_esr:*:*:*:*:*:*:*:* Versions before 78.12 Vulnerable ·Mozilla
  • cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:* Versions before 78.12 Vulnerable ·Mozilla

Remediation

  • Fix · CNA Thunderbird (Mozilla) Fixed in 78.12
  • Fix · CNA Firefox ESR (Mozilla) Fixed in 78.12
  • Fix · CNA Firefox (Mozilla) Fixed in 90

Red Hat 8 advisories

  • RHSA-2021:2914 Released 2021-07-27 · Red Hat rating Important
    thunderbird security update
    • Red Hat Enterprise Linux AppStream EUS (v. 8.2) thunderbird-78.12.0-2.el8_2
  • RHSA-2021:2881 Released 2021-07-26 · Red Hat rating Important
    thunderbird security update
    • Red Hat Enterprise Linux Client (v. 7) thunderbird-78.12.0-2.el7_9
    • Red Hat Enterprise Linux Server Optional (v. 7) thunderbird-78.12.0-2.el7_9
    • Red Hat Enterprise Linux Workstation (v. 7) thunderbird-78.12.0-2.el7_9
  • RHSA-2021:2883 Released 2021-07-26 · Red Hat rating Important
    thunderbird security update
    • Red Hat Enterprise Linux AppStream (v. 8) thunderbird-78.12.0-3.el8_4
Show 5 more Red Hat advisories
  • RHSA-2021:2882 Released 2021-07-26 · Red Hat rating Important
    thunderbird security update
    • Red Hat Enterprise Linux AppStream EUS (v. 8.1) thunderbird-78.12.0-2.el8_1
  • RHSA-2021:2743 Released 2021-07-15 · Red Hat rating Important
    firefox security update
    • Red Hat Enterprise Linux AppStream (v. 8) firefox-78.12.0-1.el8_4
  • RHSA-2021:2742 Released 2021-07-15 · Red Hat rating Important
    firefox security update
    • Red Hat Enterprise Linux AppStream EUS (v. 8.2) firefox-78.12.0-1.el8_2
  • RHSA-2021:2741 Released 2021-07-15 · Red Hat rating Important
    firefox security update
    • Red Hat Enterprise Linux Client (v. 7) firefox-78.12.0-1.el7_9
    • Red Hat Enterprise Linux Client Optional (v. 7) firefox-78.12.0-1.el7_9
    • Red Hat Enterprise Linux Server (v. 7) firefox-78.12.0-1.el7_9
    • Red Hat Enterprise Linux Server Optional (v. 7) firefox-78.12.0-1.el7_9
    • Red Hat Enterprise Linux Workstation (v. 7) firefox-78.12.0-1.el7_9
    • Red Hat Enterprise Linux Workstation Optional (v. 7) firefox-78.12.0-1.el7_9
  • RHSA-2021:2740 Released 2021-07-15 · Red Hat rating Important
    firefox security update
    • Red Hat Enterprise Linux AppStream EUS (v. 8.1) firefox-78.12.0-1.el8_1

Fixed in the same release

Records fixed by the same vendor advisory or release, as the CNA lists them.

  • Release ·

    Mozilla Firefox 90

    8 records Highest priority Priority MEDIUM 6 MEDIUM, 2 LOW

    Other records, highest priority first

    • TI-2021-10588 If a user had granted a permission to a webpage and saved that grant, any webpage running…Priority MEDIUM 44
    • TI-2021-10587 Use after free in Mozilla ThunderbirdPriority MEDIUM 41
    • TI-2021-10594 Out-of-bounds write in Mozilla FirefoxPriority MEDIUM 40
    Show all 8 records →
  • Release ·

    Mozilla Thunderbird 78.12

    3 records Highest priority Priority MEDIUM 2 MEDIUM, 1 LOW

    Other records, highest priority first

    • TI-2021-10587 Use after free in Mozilla ThunderbirdPriority MEDIUM 41
    • TI-2021-10586 If Thunderbird was configured to use STARTTLS for an IMAP connection, and an attacker…Priority LOW 29
    Show all 3 records →
Show 1 more group
  • Release ·

    Mozilla Firefox ESR 78.12

    2 records Highest priority Priority MEDIUM 2 MEDIUM

    Other records, highest priority first

    • TI-2021-10587 Use after free in Mozilla ThunderbirdPriority MEDIUM 41
    Show all 2 records →

Vendor assessments

Red Hat

Red Hat rating: Important. Red Hat's page for this CVE →

ProductStatusPlan or fix
Red Hat Enterprise Linux 6AffectedNo fix planned: Out of support scope
Red Hat Enterprise Linux AppStream (v. 8)Fixed RHSA-2021:2743, RHSA-2021:2883
Red Hat Enterprise Linux AppStream EUS (v. 8.1)Fixed RHSA-2021:2740, RHSA-2021:2882
Red Hat Enterprise Linux AppStream EUS (v. 8.2)Fixed RHSA-2021:2742, RHSA-2021:2914
Red Hat Enterprise Linux Client (v. 7)Fixed RHSA-2021:2741, RHSA-2021:2881
Red Hat Enterprise Linux Client Optional (v. 7)Fixed RHSA-2021:2741
Red Hat Enterprise Linux Server (v. 7)Fixed RHSA-2021:2741
Red Hat Enterprise Linux Server Optional (v. 7)Fixed RHSA-2021:2741, RHSA-2021:2881
Red Hat Enterprise Linux Workstation (v. 7)Fixed RHSA-2021:2741, RHSA-2021:2881
Red Hat Enterprise Linux Workstation Optional (v. 7)Fixed RHSA-2021:2741

Timeline

  1. 2026-10-02 Threatist record created from CVE-2021-29976
  2. 2026-10-03 Alias added: GHSA-jv3x-w8ff-cj2g

References

Advisory 6

  • TI-2024-08981 Use after free in Mozilla Firefox KEVCVSS 3.1CRITICAL 9.8
  • TI-2022-09832 Use after free in Mozilla Firefox KEVCVSS 3.1CRITICAL 9.6
  • TI-2019-08769 Improper input validation in Mozilla Firefox ESR KEVCVSS 3.1CRITICAL 10.0
  • TI-2010-03577 Mozilla Firefox 3.5.x through 3.5.14 and 3.6.x through 3.6.11, Thunderbird 3.1.6 before… KEVCVSS 3.1CRITICAL 9.8
  • TI-2023-04799 Out-of-bounds write in Google Chrome KEVCVSS 3.1HIGH 8.8
  • TI-2023-04477 Out-of-bounds write in Google Chrome KEVCVSS 3.1HIGH 8.8
See all 3444 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences