CVE-2020-12418: 
NixOS vulnerability analysis and mitigation

CVE-2020-12418 is a high-severity information disclosure vulnerability discovered in Mozilla Firefox and Thunderbird that was disclosed on June 30, 2020. The vulnerability affects Firefox ESR < 68.10, Firefox < 78, and Thunderbird < 68.10.0. The issue occurs when manipulating individual parts of a URL object, which could cause an out-of-bounds read, potentially leaking process memory to malicious JavaScript (Mozilla Advisory, NVD).

The vulnerability stems from improper handling of URL objects in Mozilla's networking library. When individual parts of a URL object are manipulated, it could trigger an out-of-bounds read condition. This could allow malicious JavaScript to access process memory that should be inaccessible. The vulnerability has a CVSS v3.1 base score of 6.5 (Medium), with attack vector being Network, attack complexity Low, privileges required None, user interaction Required, scope Unchanged, confidentiality impact High, and integrity and availability impact None (Ubuntu).

The primary impact of this vulnerability is information disclosure. If successfully exploited, an attacker could leak process memory through malicious JavaScript, potentially exposing sensitive information from the browser's memory space. In Thunderbird, while the vulnerability exists, it cannot be exploited through email alone since scripting is disabled when reading mail, but it remains a potential risk in browser-like contexts (Mozilla Advisory).

The vulnerability requires user interaction and can be triggered by visiting a specially crafted webpage containing malicious JavaScript. The exploit involves manipulating URL objects to cause an out-of-bounds read condition. Mozilla's security team identified that the vulnerability could be more obvious and easy to exploit than initially estimated, leading to careful timing of the patch release (Mozilla Bug).

The vulnerability was fixed in Firefox 78, Firefox ESR 68.10, and Thunderbird 68.10.0. Users are advised to upgrade to these versions or later. The fix involves properly handling query and reference lengths in URL objects. No workarounds were available prior to the patch, making upgrading to a fixed version the only solution (Red Hat, Gentoo).

The vulnerability was discovered and reported by Marcin 'Icewall' Noga of Cisco Talos. Mozilla coordinated the disclosure with the researcher and planned the release of the fix for June 30th, 2020. The fix was carefully timed due to the potential ease of exploitation, with Mozilla developers choosing to delay the patch landing until closer to the release date (Mozilla Bug).