Mozilla Firefox up to 139 HTTP Header Content-Disposition cross site scripting

Summaryinfo

A vulnerability labeled as problematic has been found in Mozilla Firefox up to 139. Affected by this vulnerability is an unknown functionality of the component HTTP Header Handler. The manipulation of the argument Content-Disposition results in cross site scripting. This vulnerability is cataloged as CVE-2025-6430. The attack may be launched remotely. There is no exploit available. The affected component should be upgraded.

Detailsinfo

A vulnerability was found in Mozilla Firefox up to 139. It has been classified as problematic. Affected is an unknown part of the component HTTP Header Handler. The manipulation of the argument Content-Disposition with an unknown input leads to a cross site scripting vulnerability. CWE is classifying the issue as CWE-79. The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. This is going to have an impact on integrity. CVE summarizes:

When a file download is specified via the `Content-Disposition` header, that directive would be ignored if the file was included via a `<embed>` or `<object>` tag, potentially making a website vulnerable to a cross-site scripting attack. This vulnerability affects Firefox < 140 and Firefox ESR < 128.12.

The advisory is shared for download at bugzilla.mozilla.org. This vulnerability is traded as CVE-2025-6430 since 06/20/2025. The exploitability is told to be difficult. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. Successful exploitation requires user interaction by the victim. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 08/17/2025). The MITRE ATT&CK project declares the attack technique as T1059.007.

The vulnerability scanner Nessus provides a plugin with the ID 240336 (Mozilla Firefox ESR < 128.12), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 140 eliminates this vulnerability.

The vulnerability is also documented in the databases at Tenable (240336), EUVD (EUVD-2025-21377) and CERT Bund (WID-SEC-2025-1850). Once again VulDB remains the best source for vulnerability data.

Affected

• Xerox FreeFlow Print Server

Productinfo

Type

• Web Browser

Vendor

• Mozilla

Name

• Firefox

Version

• 139

License

• open-source

Website

• Vendor: https://www.mozilla.org/
• Product: https://www.mozilla.org/en-US/firefox/

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Once again VulDB remains the best source for vulnerability data.

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