CVE-2020-15663: 
NixOS vulnerability analysis and mitigation

CVE-2020-15663 is a high-impact security vulnerability discovered in Mozilla's Firefox and Thunderbird applications. The vulnerability affects the Mozilla Maintenance Service on Windows systems when Firefox or Thunderbird is installed in a user-writable directory. The issue was disclosed on August 25, 2020, and affects Firefox versions < 80, Thunderbird < 78.2, Thunderbird < 68.12, Firefox ESR < 68.12, and Firefox ESR < 78.2 (Mozilla Advisory, CVE Details).

The vulnerability stems from the Mozilla Maintenance Service's handling of the updater.exe file. While the service verifies that updater.exe is signed by Mozilla, it does not validate the file version. This oversight allows an attacker to replace the current updater.exe with an older, vulnerable version. The service would then execute this downgraded updater.exe with system privileges, potentially leading to arbitrary code execution with System Privileges. This vulnerability only affects Windows operating systems, with other operating systems remaining unaffected (Mozilla Advisory).

The vulnerability allows for local privilege escalation on Windows systems where Firefox or Thunderbird is installed in a user-writable directory. An attacker with non-administrative privileges could exploit this vulnerability to execute arbitrary code with System Privileges, effectively gaining complete control over the affected system (Mozilla Advisory).

The vulnerability requires local access to the system and Firefox/Thunderbird to be installed in a user-writable location. The exploit involves replacing the updater.exe with an older vulnerable version and manipulating the update process to execute arbitrary code with elevated privileges (CVE Details).

The vulnerability was patched in Firefox 80, Firefox ESR 78.2, Firefox ESR 68.12, Thunderbird 78.2, and Thunderbird 68.12. Users should update their installations to these versions or newer to protect against this vulnerability. Additionally, installing Firefox and Thunderbird in protected directories (not user-writable) can help prevent exploitation (Mozilla Advisory).