CVE-2025-5986

Name: CVE-2025-5986
Creator: NVD / NIST
Published: 2025-06-11T12:15:29.183+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 6.5/10EPSS 0.47%

Last modified Jun 17, 2026

CVE-2025-5986 is a medium-severity vulnerability rated 6.5/10 on the CVSS scale. 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. EPSS estimates a 0.47% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

6.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

EPSS Probability

0.47%

36.9th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-451

Affected Software

Vendor	Product	Versions
Mozilla	Thunderbird	< 128.11.1
Mozilla	Thunderbird	>= 135.0, < 139.0.2

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

Timeline

Published: Jun 11, 2025
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2025-5986?

How severe is CVE-2025-5986?

CVE-2025-5986 has a CVSS score of 6.5/10 (MEDIUM severity). The EPSS model estimates a 0.47% probability of exploitation in the next 30 days.

How do I fix CVE-2025-5986?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2025-5986?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST