Vulnerability Description
Thunderbird processes the X-Mozilla-External-Attachment-URL header to handle attachments which can be hosted externally. When an email is opened, Thunderbird accesses the specified URL to determine file size, and navigates to it when the user clicks the attachment. Because the URL is not validated or sanitized, it can reference internal resources like chrome:// or SMB share file:// links, potentially leading to hashed Windows credential leakage and opening the door to more serious security issues. This vulnerability was fixed in Thunderbird 137.0.2 and Thunderbird 128.9.2.
CVSS Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Thunderbird | < 128.9.2 |
Related Weaknesses (CWE)
References
- https://bugzilla.mozilla.org/show_bug.cgi?id=1955372Permissions Required
- https://www.mozilla.org/security/advisories/mfsa2025-26/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2025-27/Vendor Advisory
FAQ
What is CVE-2025-3522?
CVE-2025-3522 is a vulnerability with a CVSS score of 6.3 (MEDIUM). Thunderbird processes the X-Mozilla-External-Attachment-URL header to handle attachments which can be hosted externally. When an email is opened, Thunderbird accesses the specified URL to determine f...
How severe is CVE-2025-3522?
CVE-2025-3522 has been rated MEDIUM with a CVSS base score of 6.3/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2025-3522?
Check the references section above for vendor advisories and patch information. Affected products include: Mozilla Thunderbird.