CVE-2020-6107: 
NixOS vulnerability analysis and mitigation

An exploitable information disclosure vulnerability exists in the dev_read functionality of F2fs-Tools F2fs.Fsck 1.13. The vulnerability, identified as CVE-2020-6107, was discovered by Lilith of Cisco Talos and publicly disclosed on October 14, 2020. The F2fs-tools set of utilities is specifically used for creating, checking, and fixing Flash-Friendly File System (F2FS) files, which has been increasingly replacing ext4 in embedded devices due to its optimization for eMMC chips and SD cards (Talos Report).

The vulnerability exists in the dev_read functionality where a specially crafted f2fs filesystem can cause an uninitialized read. The issue stems from improper handling of read syscall return values, where dev_read only checks for -1 return values but doesn't properly handle EOF conditions (return value 0). This oversight results in the void *buf parameter being filled with uninitialized heap data instead of disk contents. The vulnerability has been assigned a CVSS v3.x base score of 5.5 (MEDIUM) with vector CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N by NIST, while Talos assigned it a score of 4.4 (MEDIUM) with vector CVSS:3.0/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N (NVD, Talos Report).

The vulnerability can lead to information disclosure, potentially exposing sensitive information through uninitialized heap data being exposed when reading from the filesystem. An attacker can trigger this vulnerability by providing a malicious file to the target system (Talos Report).

The vulnerability requires local access and can be triggered by providing a malicious file to the system. The attack complexity is considered low, though privilege requirements and user interaction needs differ between NIST and Talos assessments (NVD).

Users should upgrade to F2fs-tools version 1.14.0 or later to address this vulnerability. This was confirmed in the Gentoo Linux Security Advisory (GLSA 202101-26) which recommended users to upgrade their systems using the command: emerge --ask --oneshot --verbose ">=sys-fs/f2fs-tools-1.14.0" (Gentoo Advisory).

The vulnerability was initially disclosed to the vendor on May 8, 2020, followed by 60-day and 90-day follow-ups. After the vendor failed to respond within the 90-day deadline, Cisco Talos released a zero-day public disclosure on October 14, 2020, in accordance with their coordinated disclosure policy (Talos Report).