A critical vulnerability has been discovered in the Linux kernel, which potentially allows malicious users to gain unauthorized access and escalate their privileges on the affected system. Identified as CVE-2023-0386, this security issue specifically impacts the OverlayFS subsystem, a union filesystem that supports merging multiple directories into one.

In this post, we will delve into the details of this vulnerability, and provide the necessary steps to mitigate the risk associated with it. We will also explore code snippets, links to original references, and a brief analysis of the exploit to better understand how it affects systems.

The Vulnerability Explained

CVE-2023-0386 stems from the way OverlayFS handles the execution of setuid files with capabilities on a Linux system. A local user can exploit this issue by copying a capable file from a nosuid mount to another mount, which allows unauthorized access to setuid file execution, leading to privilege escalation - a critical security flaw.

This vulnerability is crucial and must be dealt with promptly to prevent any unauthorized access or compromising of the affected systems.

The code snippet that forms the basis of this vulnerability can be found below

mnt_of = path.dentry->d_sb->s_fs_info;
err = -EXDEV;
if (mnt_of != mnt_userns)
 goto out;

To give a little context, the code checks if the specified user namespace matches the filesystem's namespace. If it does not match, the error code EXDEV is returned, and the process is aborted. However, the checking is done inappropriately, which allows the execution of the setuid file with capabilities, resulting in the exploitation of the vulnerability.

Exploiting the Vulnerability

The exploit details for this vulnerability involve a series of steps that a malicious user can undertake to gain unauthorized access and escalate their privileges on the system.

1. A local user first needs to mount a file system with the nosuid option, which prevents the execution of setuid files with elevated privileges.
2. The user then needs to copy a capable file from this nosuid mount to an unprivileged OverlayFS mount.
3. Once the file is copied, the user can exploit the vulnerability by executing the copied file, which subsequently grants them the elevated privileges they desire to compromise the system.

- Official CVE Details: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-0386
- Linux Kernel Patch: https://lore.kernel.org/lkml/20220208002022.2396-1-sandalle@camelpunch.com/

Update the Linux kernel to the latest version, which includes the patch to fix the issue.

2. If you cannot update the kernel immediately, manually apply the patch provided by the Linux kernel mailing list (patch link).


CVE-2023-0386 is a critical security vulnerability that has the potential to expose sensitive data and compromise the integrity of your system. As a system administrator or developer, it is your responsibility to stay informed about such vulnerabilities, and take appropriate steps to ensure that your systems are protected.

By updating the Linux kernel or applying the recommended patch, and maintaining a robust security policy, you can effectively safeguard your systems against CVE-2023-0386 and other similar vulnerabilities.


Published on: 03/22/2023 21:15:00 UTC
Last modified on: 04/20/2023 09:15:00 UTC