CVE-2023-53861

Vulnerability

Overview

CVE-2023-53861 is a NULL pointer dereference vulnerability in the Linux kernel's ext4 filesystem, specifically in the ext4_mb_good_group function. The function performs a group corruption check that accesses memory of the group descriptor (grp) without first verifying that the pointer is non-NULL. If grp is NULL, this access triggers a kernel crash (oops). The root cause is missing input validation before dereferencing the pointer [1][2][3].

Exploitation

Exploitation requires local access to the system and the ability to trigger ext4 block allocation operations that call ext4_mb_good_group with a NULL group pointer. This could occur through crafted filesystem operations or by mounting a maliciously prepared ext4 filesystem. No special privileges beyond local user access are necessary to trigger the crash, making it a denial-of-service vector.

Impact

A successful exploit results in a kernel NULL pointer dereference, leading to a system crash (panic) and denial of service. The vulnerability does not appear to allow privilege escalation or arbitrary code execution based on the available information; the primary impact is availability.

Mitigation

The fix adds a NULL check for grp before the corruption check, preventing the dereference. The patch has been applied to the Linux kernel stable branches as seen in commits [1][2][3]. Users should update to a kernel version containing the fix or apply the relevant patch. No workaround is available other than updating.