CVE-2020-25220: 
Linux Debian vulnerability analysis and mitigation

CVE-2020-25220 is a use-after-free vulnerability discovered in the Linux kernel versions 4.9.x before 4.9.233, 4.14.x before 4.14.194, and 4.19.x before 4.19.140. The issue occurred because skcd->no_refcnt was not considered during a backport of a CVE-2020-14356 patch. This vulnerability is related to the cgroups feature (NVD, CVE).

The vulnerability exists in the cgroup subsystem's handling of socket references to cgroups. In some cgroup configurations, this could lead to a use-after-free condition. The issue stems from improper handling of the skcd->no_refcnt flag during socket cloning operations. The vulnerability was introduced when backporting a fix for CVE-2020-14356, which did not properly account for all reference counting scenarios (Debian).

When successfully exploited, this vulnerability could lead to denial of service (crash or memory corruption) or possibly privilege escalation. The vulnerability has been assigned a CVSS v3.1 Base Score of 7.8 (HIGH) with vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H (NetApp Advisory).

The vulnerability requires local access to the system and can be triggered by a local user in certain cgroup configurations. The attack complexity is considered low, but it requires low privileges to execute (NVD).

The vulnerability has been fixed in Linux kernel versions 4.9.233, 4.14.194, and 4.19.140. Users are advised to upgrade their kernel to these versions or later. The fix involves proper handling of the skcd->no_refcnt flag during socket operations (Kernel Commit).