CVE-2023-53794 in Linux
Summary
by MITRE • 12/09/2025
In the Linux kernel, the following vulnerability has been resolved:
cifs: fix session state check in reconnect to avoid use-after-free issue
Don't collect exiting session in smb2_reconnect_server(), because it will be released soon.
Note that the exiting session will stay in server->smb_ses_list until it complete the cifs_free_ipc() and logoff() and then delete itself from the list.
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Analysis
by VulDB Data Team • 03/29/2026
The vulnerability identified as CVE-2023-53794 represents a critical use-after-free condition within the Linux kernel's CIFS (Common Internet File System) implementation. This flaw specifically affects the smb2_reconnect_server() function which handles session reconnection logic for SMB2 protocol implementations. The issue stems from improper session state management during the reconnection process where the system attempts to reference a session that is already marked for deletion but has not yet been fully released from memory. This creates a scenario where memory that has been deallocated is still being accessed, potentially leading to system instability or arbitrary code execution.
The technical root cause of this vulnerability lies in the improper handling of session lifecycle management within the CIFS subsystem. When the smb2_reconnect_server() function executes, it attempts to collect sessions that are in an exiting state from the server->smb_ses_list data structure. However, these sessions are not immediately removed from the list as they undergo the cifs_free_ipc() cleanup process and logoff operations. The session remains in the list structure until these cleanup procedures complete, which can take some time. During this interim period, if the reconnect function attempts to reference these sessions, it accesses memory that has already been freed, creating the use-after-free condition that represents the core vulnerability.
This vulnerability has significant operational impact within enterprise environments that rely on CIFS/SMB file sharing protocols for data access and storage. The use-after-free condition can lead to system crashes, denial of service scenarios, or potentially enable privilege escalation attacks depending on the specific system configuration and attack vectors available. Network file servers, storage arrays, and any system that maintains persistent CIFS connections are at risk, particularly in environments where frequent reconnection attempts occur or where session management is heavily utilized. The vulnerability affects systems running Linux kernels with CIFS implementations that handle SMB2 protocol connections, making it relevant across a broad range of enterprise and cloud infrastructure deployments.
The mitigation strategy for CVE-2023-53794 involves applying the kernel patch that prevents the smb2_reconnect_server() function from collecting sessions that are already in the process of exiting. This fix ensures that only valid, active sessions are referenced during reconnection attempts, eliminating the race condition that leads to the use-after-free scenario. System administrators should prioritize updating their Linux kernel versions to include this patch, particularly in production environments where CIFS connectivity is critical. The fix aligns with common security practices for preventing use-after-free vulnerabilities and follows the principle of least privilege by ensuring that session references are only maintained for valid, active sessions. Organizations should also implement monitoring for unusual reconnection patterns or system instability that might indicate exploitation attempts, as the vulnerability could potentially be leveraged for more sophisticated attacks in combination with other exploit primitives.
This vulnerability maps directly to CWE-416, which specifically addresses the use-after-free condition in software development practices. The issue demonstrates poor memory management and lifecycle handling within kernel space code, representing a fundamental flaw in how session references are managed during asynchronous operations. From an ATT&CK perspective, this vulnerability could be leveraged in initial access or privilege escalation phases of an attack, particularly in environments where CIFS services are exposed to untrusted networks or where attackers can influence session reconnection patterns. The vulnerability's impact is further amplified by the fact that it occurs in kernel space, potentially allowing attackers to gain elevated privileges or cause system-wide disruptions when successfully exploited.