CVE-2025-5986

What it is

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 was fixed in Thunderbird 128.11.1 and Thunderbird 139.0.2.

At a glance

Exploitability

Can be exploited over the network without logging in, but needs a user to act. High risk of service disruption.

Exploit odds

0.6% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2025-06-11 12:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 09:49 UTC Last updatedMost recent change to the record

Details

Published

2025-06-11 12:15 UTC

Last modified

2026-06-17 09:49 UTC

Exploit probability

0.6% · EPSS, next 30 days

Weakness

CWE-451

Record status

Modified

Affected

• Mozilla Thunderbird < 128.11.1
• Mozilla Thunderbird < 139.0.2

Attack profile CVSS 3.1 · 6.5

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

Required

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High