CVE-2025-5986: Unsolicited File Download, Disk Space Exhaustion, and Credential Leakage via mailbox:/// Links
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.
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2025-5986?
CVE-2025-5986 is classified as a high-severity vulnerability due to potential abuse leading to unsolicited file downloads.
What systems are affected by CVE-2025-5986?
CVE-2025-5986 affects Mozilla Thunderbird versions up to 128.11.1 and 139.0.2.
How do I fix CVE-2025-5986?
To mitigate CVE-2025-5986, update your Thunderbird installation to the latest version provided by Mozilla.
What kind of files are automatically downloaded due to CVE-2025-5986?
CVE-2025-5986 can trigger automatic downloads of .pdf files without user consent.
Can CVE-2025-5986 fill my disk space?
Yes, CVE-2025-5986 can be exploited to fill disk space with unwanted data.