#VU111896 Input validation error in Mozilla Firefox and Firefox for Android - CVE-2025-6435

Vulnerability identifier: #VU111896

Vulnerability risk: Low

CVSSv4.0: 4.5 [CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:U/U:Clear]

CVE-ID: CVE-2025-6435

CWE-ID: CWE-20

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
Mozilla Firefox
Client/Desktop applications / Web browsers
Firefox for Android
Mobile applications / Apps for mobile phones

Vendor: Mozilla

Description

The vulnerability allows a remote attacker to manipulate file a downloaded extension.

The vulnerability exists due to insufficient validation of user-supplied input. 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.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

Mozilla Firefox: 130.0 - 139.0.4

Firefox for Android: 130.0 - 139.0.3

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External links
https://www.mozilla.org/en-US/security/advisories/mfsa2025-51/
https://bugzilla.mozilla.org/show_bug.cgi?id=1961777
https://bugzilla.mozilla.org/show_bug.cgi?id=1950056

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.