Read the docs
TI-2021-19419 Aliases CVE-2021-43529GHSA-82q7-2fg2-4gcj

Out-of-bounds write in Mozilla Thunderbird

Priority MEDIUM 49CWE-787Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
Code execution
Confidentiality · integrity · availability
High · High · High
Fix status
Partial Red Hat: 6 fixed, 1 without a fix

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

Summary

Thunderbird versions prior to 91.3.0 are vulnerable to the heap overflow described in CVE-2021-43527 when processing S/MIME messages. Thunderbird versions 91.3.0 and later will not call the vulnerable code when processing S/MIME messages that contain certificates with DER-encoded DSA or RSA-PSS signatures.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00469 40th percentileScored 2026-11-07
Fix Partial Thunderbird (Mozilla): 91.3.0Red Hat: 4 advisoriesRed Hat: 6 fixed, 1 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
Yes
Technical impact
Total

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
MozillaThunderbirdbefore 91.3.091.3.0Patch availableCNA
  • Thunderbird VendorMozilla Affected before 91.3.0 Fixed in 91.3.0 Patch available CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*before 91.3.0VulnerableMozilla
  • cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:* Versions before 91.3.0 Vulnerable ·Mozilla

Remediation

  • Fix · CNA Thunderbird (Mozilla) Fixed in 91.3.0

Red Hat 4 advisories

  • RHSA-2021:4134 Released 2021-11-04 · Red Hat rating Important
    thunderbird security update
    • Red Hat Enterprise Linux Client (v. 7) thunderbird-91.3.0-2.el7_9
    • Red Hat Enterprise Linux Server Optional (v. 7) thunderbird-91.3.0-2.el7_9
    • Red Hat Enterprise Linux Workstation (v. 7) thunderbird-91.3.0-2.el7_9
  • RHSA-2021:4130 Released 2021-11-04 · Red Hat rating Important
    thunderbird security update
    • Red Hat Enterprise Linux AppStream (v. 8) thunderbird-91.3.0-2.el8_4
  • RHSA-2021:4132 Released 2021-11-04 · Red Hat rating Important
    thunderbird security update
    • Red Hat Enterprise Linux AppStream EUS (v. 8.2) thunderbird-91.3.0-2.el8_2
Show 1 more Red Hat advisories
  • RHSA-2021:4133 Released 2021-11-04 · Red Hat rating Important
    thunderbird security update
    • Red Hat Enterprise Linux AppStream EUS (v. 8.1) thunderbird-91.3.0-2.el8_1

Vendor assessments

Red Hat

Red Hat rating: Critical. 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-2021:4130
Red Hat Enterprise Linux AppStream EUS (v. 8.1)Fixed RHSA-2021:4133
Red Hat Enterprise Linux AppStream EUS (v. 8.2)Fixed RHSA-2021:4132
Red Hat Enterprise Linux Client (v. 7)Fixed RHSA-2021:4134
Red Hat Enterprise Linux Server Optional (v. 7)Fixed RHSA-2021:4134
Red Hat Enterprise Linux Workstation (v. 7)Fixed RHSA-2021:4134
Not affected: 1 product
  • Red Hat Enterprise Linux 9

Timeline

  1. 2026-10-02 Threatist record created from CVE-2021-43529
  2. 2026-10-03 Alias added: GHSA-82q7-2fg2-4gcj

References

Other 1

  • 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 2067 →

Sources

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