CVE-2025-3877

Name	CVE-2025-3877
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 < 128.10.1 and Thunderbird < 138.0.1.
Source	CVE (at NVD; CERT, LWN, oss-sec, fulldisc, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)
References	DLA-4167-1, DSA-5921-1

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
thunderbird (PTS)	bullseye	1:115.12.0-1~deb11u1	vulnerable
	bullseye (security)	1:128.10.1esr-1~deb11u1	fixed
	bookworm	1:128.10.0esr-1~deb12u1	vulnerable
	bookworm (security)	1:128.10.1esr-1~deb12u1	fixed
	trixie	1:128.10.0esr-1	vulnerable
	sid	1:128.10.1esr-1	fixed

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version	Origin
thunderbird	source	bullseye	1:128.10.1esr-1~deb11u1	DLA-4167-1
thunderbird	source	bookworm	1:128.10.1esr-1~deb12u1	DSA-5921-1
thunderbird	source	(unstable)	1:128.10.1esr-1

https://www.mozilla.org/en-US/security/advisories/mfsa2025-34/#CVE-2025-3877