Arbitrary file upload in Mozilla Firefox
CVE-2025-6435
If a user saved a response from the Network tab in Devtools using the Save As context menu option, that file may not have been saved with the `.download` file extension. This could have led to the user inadvertently running a malicious executable. This vulnerability was fixed in Firefox 140 and Thunderbird 140.
Vulnerability class: Unrestricted File Upload
EPSS: 0.004 (29.9th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 8.1 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.
Affected products
- Mozilla Firefox — versions 140
- Mozilla Thunderbird — versions 140
Weakness classification (CWE)
References
- security@mozilla.org (Permissions Required)
- security@mozilla.org (Permissions Required)
- security@mozilla.org (Vendor Advisory)
- security@mozilla.org (Vendor Advisory)
Frequently asked questions
- What is CVE-2025-6435?
- CVE-2025-6435 is a high-severity vulnerability in Mozilla Firefox, classified under Unrestricted Upload of File with Dangerous Type. CVSS score: 8.1/10. Published 2025-06-24.
- How severe is CVE-2025-6435?
- High severity. CVSS v3 base score is 8.1 out of 10.