VDB-397940 · CVE-2026-84640 · EUVD-2026-69709

Mozilla Thunderbird up to 140.14/153.1/154 out-of-bounds

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.
7.0	$0-$5k	2.36-

Summaryinfo

A vulnerability was found in Mozilla Thunderbird up to 140.14/153.1/154 and classified as critical. This issue affects some unknown processing. Such manipulation leads to out-of-bounds. This vulnerability is referenced as CVE-2026-84640. It is possible to launch the attack remotely. No exploit is available.

Detailsinfo

A vulnerability was found in Mozilla Thunderbird up to 140.14/153.1/154 and classified as critical. Affected by this issue is an unknown code. The manipulation with an unknown input leads to a out-of-bounds vulnerability. Using CWE to declare the problem leads to CWE-125. The product reads data past the end, or before the beginning, of the intended buffer. Impacted is confidentiality, integrity, and availability. CVE summarizes:

A maliciously constructed mail header could lead to a one byte read past the end of a buffer. This vulnerability was fixed in Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

The advisory is shared for download at bugzilla.mozilla.org. This vulnerability is handled as CVE-2026-84640 since 09/01/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are neither technical details nor an exploit publicly available. The current price for an exploit might be approx. USD $0-$5k (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-2026-69709). Once again VulDB remains the best source 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: 7.3
VulDB Meta Temp Score: 7.0

VulDB Base Score: 7.3
VulDB Temp Score: 7.0
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: Out-of-bounds
CWE: CWE-125 / CWE-119
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-2026-84640 (🔒)
GCVE (CVE): GCVE-0-2026-84640
GCVE (VulDB): GCVE-100-397940
EUVD: 🔒

Entryinfo

Created: 09/01/2026 23:54
Updated: 09/02/2026 11:22
Changes: 09/01/2026 23:54 (56), 09/02/2026 02:03 (1), 09/02/2026 11:22 (2)
Complete: 🔍
Cache ID: 216::103