CVE-2025-5986 Unsolicited File Download, Disk Space Exhaustion, and Credential Leakage via mailbox:/// Links
Attackers can force unsolicited file downloads causing disk exhaustion or leak Windows credentials via SMB links when viewing crafted HTML emails.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2025-5986?
CVE-2025-5986 is a medium-severity vulnerability in Mozilla Thunderbird, published on 11 Jun 2025. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official 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 was fixed in Thunderbird 128.11.1 and Thunderbird 139.0.2.
Weakness: CWE-451
Which versions are affected by CVE-2025-5986?
It affects 1 product.
Linux distribution packages (8)
thunderbird AlmaLinux:10 | All versions | 128.12.0-1.el10_0.alma.1 |
thunderbird AlmaLinux:9 | All versions | 128.12.0-1.el9_6.alma.1 |
MozillaThunderbird SUSE:Linux Enterprise Module for Package Hub 15 SP6 | All versions | 128.11.1-150200.8.224.1 |
MozillaThunderbird SUSE:Linux Enterprise Module for Package Hub 15 SP7 | All versions | 128.11.1-150200.8.224.1 |
MozillaThunderbird SUSE:Linux Enterprise Workstation Extension 15 SP6 | All versions | 128.11.1-150200.8.224.1 |
MozillaThunderbird SUSE:Linux Enterprise Workstation Extension 15 SP7 | All versions | 128.11.1-150200.8.224.1 |
MozillaThunderbird openSUSE:Leap 15.6 | All versions | 128.11.1-150200.8.224.1 |
MozillaThunderbird openSUSE:Tumbleweed | All versions | 128.11.1-2.1 |
Products include Mozilla Thunderbird.
How do I fix CVE-2025-5986?
Upgrade to a fixed version.
Is CVE-2025-5986 being exploited?
There is no known exploitation of CVE-2025-5986 in the wild and no public exploit code.
Other vulnerabilities in Mozilla Thunderbird
Sources
Also known as ALSA-2025:10195, ALSA-2025:10196, DEBIAN-CVE-2025-5986, GHSA-q7fj-77gc-45xq, SUSE-SU-2025:02158-1, UBUNTU-CVE-2025-5986 and 1 more.