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.
This page covers CVE-2025-5986 as tracked by Ubuntu, for the package thunderbird. The fix is available in version 1:128.12.0+build1-0ubuntu0.22.04.1; earlier versions remain affected.
This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. A user must be tricked into taking some action. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity none, availability high.
The score comes from this vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
UBUNTU-CVE-2025-5986 is classified as CWE-451: User Interface (UI) Misrepresentation of Critical Information. The user interface (UI) does not properly represent critical information to the user, allowing the information - or its source - to be obscured or spoofed. This is often a component in phishing attacks.
UBUNTU-CVE-2025-5986 is recorded against 1 package.
Published on 11 June 2025 and last revised on 29 July 2026. No public exploit is currently recorded for this entry. Record sourced from OSV.
ubuntu.com (Report)
www.cve.org (Report)
www.mozilla.org (Report)
bugzilla.mozilla.org (Report)
www.mozilla.org (Report)
www.mozilla.org (Report)
ubuntu.com (Advisory)
These advisories are the same class of weakness (CWE-451: User Interface (UI) Misrepresentation of Critical Information) in other software:
Each distribution ships its own build and its own fixed version. Pick the one you run:
Details
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Affected Packages
| Software | From version | Fixed in |
|---|---|---|
| thunderbird | — | 1:128.12.0+build1-0ubuntu0.22.04.1 |
References
Similar Threats
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UBUNTU-CVE-2025-5986 is rated CVSS 6.5 Medium. BotEraser monitors your WordPress installation and notifies you when software you use appears in our vulnerability database.
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