CVE-2025-5986

Published Jun 11, 2025

Last updated a day ago

Mozilla Thunderbird

Overview

AI description

Automated description summarized from trusted sources.

CVE-2025-5986 involves a vulnerability in Mozilla Thunderbird. A specially crafted HTML email using "mailbox:/// links" can trigger automatic and unsolicited downloads of .pdf files to a user's computer, potentially to the desktop or home directory. This occurs without prompting the user, even if auto-saving is disabled. This vulnerability can be exploited in several ways. Attackers could fill the user's disk with unwanted data, such as by using "/dev/urandom" on Linux systems. It can also be abused to leak Windows credentials via SMB links when the email is viewed in HTML mode. While user interaction is needed to initiate the download, techniques like visual obfuscation can be used to conceal the download trigger. Simply viewing the email in HTML mode is enough to load external content. This affects Thunderbird versions prior to 128.11.1 and 139.0.2.

Description: A crafted HTML email using mailbox:/// links can trigger automatic, unsolicited downloads of .pdf files to the user's desktop or home directory without prompting, even if auto-saving is disabled. This behavior can be abused to fill the disk with garbage data (e.g. using /dev/urandom on Linux) or to leak Windows credentials via SMB links when the email is viewed in HTML mode. While user interaction is required to download the .pdf file, visual obfuscation can conceal the download trigger. Viewing the email in HTML mode is enough to load external content. This vulnerability affects Thunderbird < 128.11.1 and Thunderbird < 139.0.2.
Source: security@mozilla.org
NVD status: Awaiting Analysis

Risk scores

CVSS 3.1

Type: Secondary
Base score: 6.5
Impact score: 3.6
Exploitability score: 2.8
Vector string: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Severity: MEDIUM

Weaknesses

134c704f-9b21-4f2e-91b3-4a467353bcc0: CWE-451

Hype score: Not currently trending

References