What is CVE-2025-5986?

CVE-2025-5986 is a medium-severity vulnerability in Mozilla Thunderbird, classified under User Interface (UI) Misrepresentation of Critical Information. CVSS score: 6.5/10. Published 2025-06-11.

How severe is CVE-2025-5986?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Is CVE-2025-5986 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Vulnerability in Mozilla Thunderbird

CVE-2025-5986

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.

EPSS: 0.005 (39.3th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H.

Affected products

Mozilla Thunderbird — versions 128.11.1, 139.0.2

Weakness classification (CWE)

CWE-451 — User Interface (UI) Misrepresentation of Critical Information

Public proof-of-concept exploits

ARPSyndicate/cve-scores

References

Frequently asked questions

What is CVE-2025-5986?: CVE-2025-5986 is a medium-severity vulnerability in Mozilla Thunderbird, classified under User Interface (UI) Misrepresentation of Critical Information. CVSS score: 6.5/10. Published 2025-06-11.
How severe is CVE-2025-5986?: Medium severity. CVSS v3 base score is 6.5 out of 10.
Is CVE-2025-5986 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.