CVE-2025-3523: thunderbird — Fix

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.

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CVSS v3.1 Score

6.4

MEDIUM

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

Weakness Type (CWE)

CWE-451 CWE-451

Affected Products

Vendor	Product	Versions
mozilla	thunderbird	< 128.9.2
mozilla	thunderbird	129.0 — 137.0.2

References

Advisories & Patches

https://www.mozilla.org/security/advisories/mfsa2025-26/ https://www.mozilla.org/security/advisories/mfsa2025-27/

Other References

https://bugzilla.mozilla.org/show_bug.cgi?id=1958385

Frequently Asked Questions

What is CVE-2025-3523? +

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. It has a CVSS v3.1 base score of 6.4 (MEDIUM).

How severe is CVE-2025-3523? +

CVE-2025-3523 has a CVSS v3.1 score of 6.4 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.

What products are affected by CVE-2025-3523? +

CVE-2025-3523 affects products from mozilla, specifically: thunderbird. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2025-3523? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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