VDB-397939 · CVE-2026-84639 · EUVD-2026-69708

Mozilla Thunderbird up to 140.14/153.1/154 uninitialized pointer

CVSS Meta Temp Score CVSS is a standardized scoring system to determine possibilities of attacks. The Temp Score considers temporal factors like disclosure, exploit and countermeasures. The unique Meta Score calculates the average score of different sources to provide a normalized scoring system.	Current Exploit Price (≈) Our analysts are monitoring exploit markets and are in contact with vulnerability brokers. The range indicates the observed or calculated exploit price to be seen on exploit markets. A good indicator to understand the monetary effort required for and the popularity of an attack.	CTI Interest Score Our Cyber Threat Intelligence team is monitoring different web sites, mailing lists, exploit markets and social media networks. The CTI Interest Score identifies the interest of attackers and the security community for this specific vulnerability in real-time. A high score indicates an elevated risk to be targeted for this vulnerability.
6.0	$0-$5k	0.47-

Summaryinfo

A vulnerability has been found in Mozilla Thunderbird up to 140.14/153.1/154 and classified as critical. This vulnerability affects unknown code. This manipulation causes uninitialized pointer. The identification of this vulnerability is CVE-2026-84639. It is possible to initiate the attack remotely. There is no exploit available.

Detailsinfo

A vulnerability has been found in Mozilla Thunderbird up to 140.14/153.1/154 and classified as critical. Affected by this vulnerability is an unknown part. The manipulation with an unknown input leads to a uninitialized pointer vulnerability. The CWE definition for the vulnerability is CWE-824. The product accesses or uses a pointer that has not been initialized. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE 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.

It is possible to read the advisory at bugzilla.mozilla.org. This vulnerability is known as CVE-2026-84639 since 09/01/2026. The exploitation appears to be easy. The attack can be launched remotely. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 09/02/2026).

The vulnerability scanner Nessus provides a plugin with the ID 342261 (Mozilla Thunderbird < 155.0), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 140.15, 153.2 or 155 eliminates this vulnerability.

The vulnerability is also documented in the databases at Tenable (342261) and EUVD (EUVD-2026-69708). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Type

Mail Client Software

Vendor

Mozilla

Name

Thunderbird

Version

License

open-source

Website

Vendor: https://www.mozilla.org/

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 6.3
VulDB Meta Temp Score: 6.0

VulDB Base Score: 6.3
VulDB Temp Score: 6.0
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

AV	AC	Au	C	I	A
💳	💳	💳	💳	💳	💳
💳	💳	💳	💳	💳	💳
💳	💳	💳	💳	💳	💳

Vector	Complexity	Authentication	Confidentiality	Integrity	Availability
Unlock	Unlock	Unlock	Unlock	Unlock	Unlock
Unlock	Unlock	Unlock	Unlock	Unlock	Unlock
Unlock	Unlock	Unlock	Unlock	Unlock	Unlock

VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Uninitialized pointer
CWE: CWE-824 / CWE-908
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined
Price Prediction: 🔍
Current Price Estimation: 🔒

0-Day	Unlock	Unlock	Unlock	Unlock
Today	Unlock	Unlock	Unlock	Unlock

Nessus ID: 342261
Nessus Name: Mozilla Thunderbird < 155.0

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Thunderbird 140.15/153.2/155

Timelineinfo

09/01/2026 Advisory disclosed
09/01/2026 +0 days CVE reserved
09/01/2026 +0 days VulDB entry created
09/02/2026 +1 days VulDB entry last update

Sourcesinfo

Vendor: mozilla.org

Advisory: bugzilla.mozilla.org
Status: Confirmed

CVE: CVE-2026-84639 (🔒)
GCVE (CVE): GCVE-0-2026-84639
GCVE (VulDB): GCVE-100-397939
EUVD: 🔒

Entryinfo

Created: 09/01/2026 23:53
Updated: 09/02/2026 11:22
Changes: 09/01/2026 23:53 (56), 09/02/2026 02:03 (1), 09/02/2026 11:22 (2)
Complete: 🔍
Cache ID: 216::103

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.