CVE-2025-8043: 
NixOS vulnerability analysis and mitigation

CVE-2025-8043 is a security vulnerability discovered in Mozilla Firefox and Thunderbird versions prior to 141.0, reported by security researcher alayersattackers. The vulnerability was disclosed on July 22, 2025, and involves incorrect URL truncation where the browser incorrectly truncates URLs towards the beginning instead of around the origin (Mozilla Advisory, NVD).

The vulnerability is classified as a User Interface (UI) Misrepresentation of Critical Information (CWE-451). It has been assigned a CVSS 3.1 Base Score of 9.8 (CRITICAL) with the vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H by CISA-ADP (NVD). The technical issue stems from the browser's URL display mechanism, where URLs with long subdomains are incorrectly truncated at the beginning rather than preserving visibility of the main domain (Mozilla Bug).

The vulnerability affects the browser's ability to properly display website origins, which could lead to URL spoofing attacks. When encountering URLs with long subdomains, the browser fails to show the main domain (eTLD+1), potentially allowing attackers to visually disguise the real domain and making it difficult for users to recognize the actual website they are visiting (Mozilla Advisory).

The vulnerability has been fixed in Firefox 141.0 and Thunderbird 141.0. Users are advised to update their installations to these versions or later to receive the security fix. The fix involves changing the truncation logic to always preserve visibility of the main domain (Mozilla Advisory, Mozilla Bug).