What’s Vulnerable › Vulnerabilities

CVE-2025-3523: User Interface (UI) Misrepresentation of attachment URL

• Severity: medium (CVSS 6.4 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-04-15 · updated 2026-06-17
• Weakness: CWE-451

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.

Affected products

• Mozilla Thunderbird: before 128.9.2; from 129.0 before 137.0.2 — fixed in 128.9.2, 137.0.2

How to fix

Upgrade to a fixed version: Mozilla Thunderbird 128.9.2, 137.0.2. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1958385
• https://www.mozilla.org/security/advisories/mfsa2025-26/
• https://www.mozilla.org/security/advisories/mfsa2025-27/

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