CVE-2026-84639CWE-457

CVE-2026-84639

Critical · published September 2, 2026

CVSS v3.1
9.1
EPSS
0%
Percentile
24.9
In the wild
Unconfirmed
What it is

Triggering an error condition in certain MIME bodies would cause uninitialized memory to be used. This vulnerability was fixed in Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

The record
Technical detail
CVSS v3.1
9.1 · CRITICAL
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
CVSS v4.0
Not supplied
EPSS
0.00323 · 24.9th percentile
Weakness
CWE-457 · Use of Uninitialized Variable
Published
2026-09-02T02:17Z
Affected products (3)
ProductVersionsFixed in
mozilla/thunderbird< 140.15.0140.15.0
mozilla/thunderbird≥ 141.0, < 153.2.0153.2.0
mozilla/thunderbird≥ 154.0, < 155.0155.0
References (4)
https://bugzilla.mozilla.org/show_bug.cgi?id=2061087 · [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 21:33Z
    Uninitialized memory in MIME parsing
    cvelistv5