CVE-2020-14361: 
NixOS vulnerability analysis and mitigation

CVE-2020-14361 is a security vulnerability discovered in X.Org Server versions before xorg-x11-server 1.20.9. The vulnerability was identified as an Integer underflow leading to heap-buffer overflow in the XkbSelectEvents function, which was discovered by Jan-Niklas Sohn working with Trend Micro Zero Day Initiative and disclosed in August 2020 (X.Org Announce).

The vulnerability exists within the handling of XkbSelectEvents requests. The specific flaw results from the lack of proper validation of user-supplied data, which can result in an integer underflow before writing to memory. The vulnerability has been assigned a CVSS v3.1 base score of 7.8 (High), with the vector string CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H (ZDI Advisory).

The vulnerability can lead to privilege escalation, allowing local attackers to execute code in the context of root. The highest threats from this vulnerability are to data confidentiality and integrity as well as system availability. On systems where the X server runs with privileged access, this could lead to local privilege elevation (MITRE CVE).

This vulnerability requires local access and low privileges to exploit. An attacker must first obtain the ability to execute low-privileged code on the target system to exploit this vulnerability. The attack complexity is considered low, requiring no user interaction (ZDI Advisory).

The vulnerability has been fixed in xorg-x11-server version 1.20.9. The fix was implemented through a patch committed to the xorg server git repository with commit ID 144849ea27230962227e62a943b399e2ab304787. Users are advised to upgrade to the patched version (X.Org Announce).

Red Hat has rated this vulnerability as having moderate impact for Red Hat Enterprise Linux 8, noting that Xorg server does not run with root privileges in their implementation (Red Hat Bugzilla).