CVE-2023-54076 in Linux
Summary
by MITRE • 12/24/2025
In the Linux kernel, the following vulnerability has been resolved:
smb: client: fix missed ses refcounting
Use new cifs_smb_ses_inc_refcount() helper to get an active reference of @ses and @ses->dfs_root_ses (if set). This will prevent @ses->dfs_root_ses of being put in the next call to cifs_put_smb_ses() and thus potentially causing an use-after-free bug.
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Analysis
by VulDB Data Team • 01/02/2026
The vulnerability identified as CVE-2023-54076 resides within the Linux kernel's server message block implementation, specifically affecting the cifs client subsystem that handles network file sharing operations. This flaw represents a critical reference counting issue that could lead to memory corruption and potential system instability when managing SMB session references. The vulnerability impacts systems utilizing the Common Internet File System protocol for network file access, particularly those implementing DFS (Distributed File System) root session handling mechanisms. The issue manifests in the improper management of session reference counts, creating conditions where memory resources may be prematurely released while still being referenced by active processes.
The technical root cause of this vulnerability stems from inadequate reference counting management within the SMB client implementation. When processing DFS root sessions, the code fails to properly increment reference counts before accessing session structures, leading to scenarios where a session reference might be released prematurely through the cifs_put_smb_ses() function. This occurs because the existing code path does not utilize the newly introduced cifs_smb_ses_inc_refcount() helper function that would properly maintain active references to both the primary session structure and its associated DFS root session. The missing reference counting creates a race condition where the session memory could be freed while other code paths still maintain pointers to it, resulting in use-after-free conditions that could be exploited for arbitrary code execution or system crashes.
The operational impact of CVE-2023-54076 extends beyond simple system instability to potentially enable privilege escalation and denial of service attacks. Systems running affected kernel versions that process SMB network traffic, particularly those utilizing DFS features, face elevated risk of exploitation. Attackers could potentially leverage this vulnerability to execute malicious code within the kernel context, bypassing normal security boundaries and potentially gaining full system control. The vulnerability is particularly concerning in enterprise environments where SMB servers and clients are extensively deployed, as it could allow unauthorized users to compromise network resources or disrupt critical file sharing services. The use-after-free condition could also be triggered through malformed network responses or crafted SMB traffic, making exploitation relatively straightforward for attackers with network access.
Mitigation strategies for CVE-2023-54076 require immediate kernel updates to versions containing the patched reference counting implementation. System administrators should prioritize patching affected systems, particularly those handling SMB traffic or operating DFS-enabled file shares. The fix implements proper reference counting through the new cifs_smb_ses_inc_refcount() helper function, ensuring that both primary sessions and DFS root sessions maintain valid references until explicitly released. Organizations should also implement network segmentation and access controls to limit SMB traffic exposure, while monitoring for unusual network activity that might indicate exploitation attempts. Security teams should verify that all systems utilizing CIFS/SMB client functionality have been updated and validate that the fix properly addresses the reference counting behavior in all code paths involving session management. This vulnerability aligns with CWE-415 and CWE-416 categories related to double free and use-after-free conditions, and represents a potential ATT&CK technique for privilege escalation through kernel exploitation.