CVE-2026-84143CWE-119CWE-200information-disclosure

CVE-2026-84143

Critical · published September 1, 2026

CVSS v3.1
9.8
EPSS
0%
Percentile
30.5
In the wild
Unconfirmed
What it is

Internally found bugs present in Thunderbird 154, Thunderbird ESR 153.1 and Thunderbird ESR 140.14. Some of these bugs showed evidence of memory corruption or another security-relevant defect and we presume that with enough effort some of these could have been exploited. This vulnerability was fixed in Firefox 155, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

The record
Technical detail
CVSS v3.1
9.8 · CRITICAL
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS v4.0
Not supplied
EPSS
0.00378 · 30.5th percentile
Weaknesses
CWE-119 · Improper Restriction of Operations within the Bounds of a Memory Buffer; CWE-200 · Exposure of Sensitive Information to an Unauthorized Actor
Published
2026-09-01T17:20Z
Affected products (6)
ProductVersionsFixed in
mozilla/firefox< 140.15.0140.15.0
mozilla/firefox≥ 141.0.0, < 153.2.0153.2.0
mozilla/firefox≥ 154.0.0, < 155.0.0155.0.0
mozilla/thunderbird< 140.15.0140.15.0
mozilla/thunderbird≥ 141.0, < 153.2.0153.2.0
mozilla/thunderbird≥ 154.0, < 155.0155.0
References (9)
https://bugzilla.mozilla.org/buglist.cgi?bug_id=2048793%2C2054645%2C2057114%2C2059109%2C2061287 · [email protected]https://bugzilla.mozilla.org/buglist.cgi?bug_id=2054631%2C2054657%2C2055007%2C2055681%2C2057107%2C2058087%2C2058088%2C2058090%2C2058095%2C2058101%2C2059183%2C2059185%2C2061301%2C2061325 · [email protected]https://bugzilla.mozilla.org/show_bug.cgi?id=2057108 · [email protected]https://www.mozilla.org/security/advisories/mfsa2026-82/ · [email protected]https://www.mozilla.org/security/advisories/mfsa2026-84/ · [email protected]https://www.mozilla.org/security/advisories/mfsa2026-85/ · [email protected]https://www.mozilla.org/security/advisories/mfsa2026-86/ · [email protected]https://www.mozilla.org/security/advisories/mfsa2026-87/ · [email protected]https://www.mozilla.org/security/advisories/mfsa2026-88/ · [email protected]
EPSS history
Timeline
  • 03 SEP 03:32Z
    EPSS moved — → 0%
    epss
  • 01 SEP 12:19Z
    Internally found bugs fixed in Firefox 155, Firefox ESR 153.2 and Firefox ESR 140.15
    cvelistv5