CVE-2026-84639

CRITICAL CVSS 3.1: 9.1 EPSS 0.32%
Updated Sep 03, 2026
Thunderbird
Parameter Value
CVSS 9.1 (CRITICAL)
Affected Versions 141.0 — 155.0
Fixed In 140.15.0
Type CWE-457
Vendor Thunderbird
Public PoC No

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.

Attack Parameters

Attack Vector
Network
Can be exploited remotely
Attack Complexity
Low
Easy to exploit
Privileges Required
None
No privileges needed
User Interaction
None
No user interaction needed

Impact Assessment

Confidentiality
High
Complete data leak
Integrity
None
No data modification
Availability
High
Complete denial of service

CVSS Vector v3.1

Weakness Type (CWE)

Vulnerable Products 3

Configuration From (including) Up to (excluding)
Mozilla Thunderbird
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*
140.15.0
Mozilla Thunderbird
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*
141.0 153.2.0
Mozilla Thunderbird
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*
154.0 155.0