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VulnerabilityPublished Updated

CVE-2025-3523: Mozilla Thunderbird · CWE-451

Affects Mozilla ThunderbirdSource CVE Database V5

0

Not known to be exploited · CVSS 6.4 Medium : upgrade to 137.0.2 or 128.9.2 when convenient.

Data as of 26 Oct 2026, 12:55 UTC

CVSS 3.1 base score
6.4Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.3% chance of exploitation in 30 days – higher than 24% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 137.0.2, 128.9.2
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:H/A:L

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 15 Apr 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 137.0.2 or 128.9.2.

Affected software

ProductAffectedFixed in
Mozilla ThunderbirdAffected
  • <128.9.2
  • <137.0.2
Fixed in
  • 128.9.2
  • 137.0.2

AI-suggested

This vulnerability has been fixed by Mozilla in Thunderbird 137.0.2 and Thunderbird ESR 128.9.2. Users and administrators should update to these versions or later to remediate the issue. No additional mitigation steps are required as the fix is officially available.

Description

When an email contains multiple attachments with external links via the X-Mozilla-External-Attachment-URL header, only the last link is shown when hovering over any attachment. Although the correct link is used on click, the misleading hover text could trick users into downloading content from untrusted sources. This vulnerability was fixed in Thunderbird 137.0.2 and Thunderbird 128.9.2.

References

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