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VulnerabilityPublished Updated

CVE-2025-5986: Mozilla Thunderbird · CWE-451

Affects Mozilla ThunderbirdSource CVE Database V5

0

Not known to be exploited · CVSS 6.5 Medium : upgrade to 128.11.1 when convenient.

Data as of 26 Oct 2026, 09:15 UTC

CVSS 3.1 base score
6.5Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.5% chance of exploitation in 30 days – higher than 47% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 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. Weaponised: 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 26 Oct 2026.

What to do

Upgrade Mozilla Thunderbird to 128.11.1.

Affected software

ProductAffectedFixed in
Mozilla ThunderbirdAffected
  • <128.11.1
Fixed in
  • 128.11.1

AI-suggested

This vulnerability is fixed in Mozilla Thunderbird versions 128.11.1 and 139.0.2. Users and administrators should update to one of these versions or later to remediate the issue. No additional mitigation is required once the update is applied. Patch status is confirmed by the Mozilla advisories MFSA2025-49 and MFSA2025-50.

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.

References

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