CVE-2025-5986

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 < 128.11.1 and Thunderbird < 139.0.2.

Category

6.5
CVSS
Severity: Medium
CVSS 3.1 •
EPSS 0.04%
Vendor Advisory mozilla.org Vendor Advisory mozilla.org
Affected: Mozilla Thunderbird
Affected: Mozilla Thunderbird
Published at:
Updated at:

References

Link Tags
https://bugzilla.mozilla.org/buglist.cgi?bug_id=1958580%2C1968012 broken link
https://www.mozilla.org/security/advisories/mfsa2025-49/ vendor advisory
https://www.mozilla.org/security/advisories/mfsa2025-50/ vendor advisory

Frequently Asked Questions

What is the severity of CVE-2025-5986?
CVE-2025-5986 has been scored as a medium severity vulnerability.
How to fix CVE-2025-5986?
To fix CVE-2025-5986, make sure you are using an up-to-date version of the affected component(s) by checking the vendor release notes. As for now, there are no other specific guidelines available.
Is CVE-2025-5986 being actively exploited in the wild?
As for now, there are no information to confirm that CVE-2025-5986 is being actively exploited. According to its EPSS score, there is a ~0% probability that this vulnerability will be exploited by malicious actors in the next 30 days.
What software or system is affected by CVE-2025-5986?
CVE-2025-5986 affects Mozilla Thunderbird, Mozilla Thunderbird.
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