Vulnerability 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.
CVSS Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Thunderbird | < 128.11.1 |
Related Weaknesses (CWE)
References
- https://bugzilla.mozilla.org/buglist.cgi?bug_id=1958580%2C1968012Broken Link
- https://www.mozilla.org/security/advisories/mfsa2025-49/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2025-50/Vendor Advisory
- https://lists.debian.org/debian-lts-announce/2025/07/msg00002.html
FAQ
What is CVE-2025-5986?
CVE-2025-5986 is a vulnerability with a CVSS score of 6.5 (MEDIUM). 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...
How severe is CVE-2025-5986?
CVE-2025-5986 has been rated MEDIUM with a CVSS base score of 6.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2025-5986?
Check the references section above for vendor advisories and patch information. Affected products include: Mozilla Thunderbird.