CVE-2026-8963

Vulnerability

A spoofing issue exists in the Web Speech component of Firefox and Thunderbird, affecting versions prior to 151 [1][2]. The vulnerability allows an attacker to misrepresent the origin or content of voice-related UI elements, potentially tricking users into interacting with a deceptive interface.

Exploitation

An attacker could exploit this vulnerability by crafting a web page or email content that triggers the Web Speech API in a way that spoofs the browser or mail client's UI. In Thunderbird, scripting is disabled when reading mail, so exploitation is limited to browser-like contexts or scenarios where scripting is enabled [2]. The attacker does not require any special privileges beyond the ability to serve content to a vulnerable user.

Impact

Successful exploitation enables an attacker to spoof UI elements, potentially leading to user confusion or manipulation. The primary impact is integrity breach through UI spoofing, which could be leveraged as a step in a larger attack chain to deceive users into granting permissions or revealing sensitive information.

Mitigation

The vulnerability is fixed in Firefox 151 and Thunderbird 151 [1][2]. Users should update to these versions or later. No workaround is available for older versions. The fix was released on May 19, 2026 [1][2]. There is no indication that this CVE is listed in the KEV.