Internally found bugs fixed in Thunderbird 155, Thunderbird ESR 153.2 and Thunderbird ESR 140.15
Summary
| CVE | CVE-2026-84143 |
|---|---|
| State | PUBLISHED |
| Assigner | mozilla |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-09-01 13:20:08 UTC |
| Updated | 2026-09-03 18:17:27 UTC |
| Description | 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. |
Risk And Classification
Primary CVSS: v3.1 9.8 CRITICAL from [email protected]
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS: 0.003780000 probability, percentile 0.308390000 (date 2026-09-04)
Problem Types: CWE-119 | CWE-200 | CWE-200 CWE-200 Exposure of Sensitive Information to an Unauthorized Actor
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | [email protected] | Primary | 9.8 | CRITICAL | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
| 3.1 | ADP | DECLARED | 9.8 | CRITICAL | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
| 3.1 | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | Secondary | 9.8 | CRITICAL | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
LowPrivileges Required
NoneUser Interaction
NoneScope
UnchangedConfidentiality
HighIntegrity
HighAvailability
HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD Known Affected Configurations (CPE 2.3)
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Mozilla | Firefox | unaffected 140.15 140.* rpm | Not specified |
| CNA | Mozilla | Firefox | unaffected 153.2 153.* rpm | Not specified |
| CNA | Mozilla | Firefox | unaffected 155 * rpm | Not specified |
| CNA | Mozilla | Thunderbird | unaffected 140.15 140.* rpm | Not specified |
| CNA | Mozilla | Thunderbird | unaffected 153.2 153.* rpm | Not specified |
| CNA | Mozilla | Thunderbird | unaffected 155 * rpm | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| bugzilla.mozilla.org/buglist.cgi | [email protected] | bugzilla.mozilla.org | Issue Tracking |
| bugzilla.mozilla.org/buglist.cgi | [email protected] | bugzilla.mozilla.org | Issue Tracking |
| bugzilla.mozilla.org/show_bug.cgi | [email protected] | bugzilla.mozilla.org | Issue Tracking |
| www.mozilla.org/security/advisories/mfsa2026-88 | [email protected] | www.mozilla.org | Vendor Advisory |
| www.mozilla.org/security/advisories/mfsa2026-85 | [email protected] | www.mozilla.org | Vendor Advisory |
| www.mozilla.org/security/advisories/mfsa2026-84 | [email protected] | www.mozilla.org | Vendor Advisory |
| www.mozilla.org/security/advisories/mfsa2026-87 | [email protected] | www.mozilla.org | Vendor Advisory |
| www.mozilla.org/security/advisories/mfsa2026-86 | [email protected] | www.mozilla.org | Vendor Advisory |
| www.mozilla.org/security/advisories/mfsa2026-82 | [email protected] | www.mozilla.org | Vendor Advisory |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: Jan de Mooij, Tom Ritter and the Mozilla Fuzzing Team (en)
There are currently no legacy QID mappings associated with this CVE.