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CVE-2025-5986VulnerabilityPublished Updated

A crafted HTML email using mailbox:/// links can trigger automatic, unsolicited downloads of .pdf files to the user's

Source GCVE Database

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Authoritative record:CVE-2025-5986· Medium 6.5

Not known to be exploited · CVSS 6.5 Medium · fixed in 139.0.2 : update affected systems when convenient.

Data as of 30 Oct 2026, 01:43 UTC

CVSS 3.1 base score
6.5Medium
How severe the flaw is on the 0–10 CVSS scale.
Patch
Available – fixed in 139.0.2, 128.11.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 11 Jun 2025

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

What to do

AI-suggested

This vulnerability is fixed in Thunderbird versions 128.11.1 and 139.0.2. Users should update to these or later versions to remediate the issue. No additional mitigation steps are required once updated, as the vendor has provided official fixes.

Description

A vulnerability in Thunderbird before versions 128.11.1 and 139.0.2 allows crafted HTML emails using mailbox:/// links to trigger automatic, unsolicited downloads of PDF files to the user's desktop or home directory without prompting, even if auto-saving is disabled. This can be exploited to exhaust disk space or leak Windows credentials via SMB links. User interaction is required to download the PDF, but visual obfuscation can hide the trigger. Viewing the email in HTML mode loads external content, enabling the issue.

References

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