CVE-2020-26971: 
NixOS vulnerability analysis and mitigation

CVE-2020-26971 is a heap buffer overflow vulnerability discovered in Mozilla Firefox's WebGL implementation. The vulnerability was disclosed on December 15, 2020, affecting Firefox versions prior to 84, Firefox ESR versions before 78.6, and Thunderbird versions before 78.6. The issue occurs when certain blit values provided by the user are not properly constrained, leading to a heap buffer overflow condition on some video drivers (Mozilla Advisory).

The vulnerability exists in the WebGL implementation where the blitFramebuffer function fails to properly validate user-controlled values. The issue specifically occurs in the StretchedBlitNearest_PixelByPixel function where destination and source addresses for memory operations can be manipulated through user input parameters. The CVSS v3.1 base score for this vulnerability is 8.8 (High), with the vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H (NVD).

When successfully exploited, this vulnerability could lead to memory corruption and potentially allow an attacker to execute arbitrary code. The heap buffer overflow condition could result in system crashes and possible remote code execution on affected systems. The vulnerability is particularly concerning as it affects multiple Mozilla products and could be triggered through malicious web content (Mozilla Advisory).

The vulnerability requires user interaction and is dependent on specific video driver configurations. Testing revealed that the exploit was reproducible on certain NVIDIA and Intel graphics configurations, though not all systems were affected. The vulnerability was confirmed to be exploitable on Windows 10 systems with specific graphics drivers (Bugzilla).

The vulnerability was addressed in Firefox 84, Firefox ESR 78.6, and Thunderbird 78.6. Users are advised to upgrade to these versions or later to receive the security fix. The fix involves implementing proper constraints on blit values to prevent buffer overflow conditions (Mozilla Advisory).