CVE-2025-3522 Leak of hashed Window credentials via crafted attachment URL

What is CVE-2025-3522?

CVE-2025-3522 is a medium-severity server-side request forgery vulnerability in Mozilla Thunderbird, published on 15 Apr 2025. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

Official 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.

Weakness: CWE-601

Which versions are affected by CVE-2025-3522?

It affects 1 product.

Products include Mozilla Thunderbird.

How do I fix CVE-2025-3522?

Upgrade to a fixed version.

Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.

Is CVE-2025-3522 being exploited?

There is no known exploitation of CVE-2025-3522 in the wild and no public exploit code.

Other vulnerabilities in Mozilla Thunderbird

• CVE-2026-92238 Ambiguous parsing of mail headers Critical 9.8
• CVE-2026-84637 Calendar invitation attachments could launch local executables Critical 9.8
• CVE-2021-43529 Memory corruption in Thunderbird Critical 9.8
• CVE-2019-11703 Memory corruption in Thunderbird Critical 9.8
• CVE-2019-11704 Memory corruption in Thunderbird Critical 9.8

All Mozilla Thunderbird vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as DEBIAN-CVE-2025-3522, GHSA-78fw-w53r-pgwg, UBUNTU-CVE-2025-3522.