CVE-2023-54076: 
Linux Kernel vulnerability analysis and mitigation

CVE-2023-54076 is a use-after-free vulnerability in the Linux kernel's SMB client (CIFS) subsystem, specifically caused by missed session (ses) reference counting in the DFS root session handling code. The flaw occurs when cifs_put_smb_ses() is called without a proper active reference on @ses->dfs_root_ses, potentially freeing memory that is still in use. It was published on December 24, 2025, and affects Linux kernel versions in the 6.4.x range up to the fix commits. The CVSS base score is listed as 0.0 (no severity rating assigned at time of publication) (ENISA EUVD, Feedly).

The root cause is improper reference counting (CWE-911: Improper Update of Reference Count) in the Linux kernel's SMB/CIFS client driver. When a session object (@ses) and its associated DFS root session (@ses->dfs_root_ses) are not properly reference-counted using the cifs_smb_ses_inc_refcount() helper before being passed to cifs_put_smb_ses(), the reference count can drop to zero prematurely, causing the session object to be freed while still accessible — a classic use-after-free condition. The fix introduces use of the cifs_smb_ses_inc_refcount() helper to acquire active references on both @ses and @ses->dfs_root_ses before any potential release. The vulnerable code range is identified between commits 8e3554150d6c and eb382196e6f6 (for one stable branch) and 8e3554150d6c to bf99f6be2d20 (for another) (ENISA EUVD).

Successful exploitation of this use-after-free vulnerability could allow a local attacker or a privileged process to cause kernel memory corruption, potentially leading to a system crash (denial of service) or, in more severe scenarios, privilege escalation or arbitrary code execution in kernel context. The affected component is the SMB/CIFS client subsystem, meaning systems that mount SMB/CIFS network shares (e.g., using DFS) are at risk. The availability impact is the most likely consequence, though memory corruption bugs of this class can sometimes be leveraged for more serious attacks depending on kernel configuration and exploit sophistication (ENISA EUVD, Feedly).

The fix is available in Linux kernel stable commits eb382196e6f6e05cfafdab797840e5a96c6e7bf0 and bf99f6be2d20146942bce6f9e90a0ceef12cbc1e, which introduce proper use of cifs_smb_ses_inc_refcount() for reference counting. Users should update to Linux kernel version 6.4.7 or later (patched), or kernel 6.5 and above. Distribution-specific patches have been issued by SUSE (SUSE-2026-0281-1, SUSE-2026-20876-1) and Oracle Linux (ELSA-2026-6037). As a workaround, avoiding the use of SMB/CIFS DFS mounts on unpatched systems reduces exposure (ENISA EUVD, Linux Security SUSE).