CVE-2024-50086 in Linux
Summary
by MITRE • 10/29/2024
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: fix user-after-free from session log off
There is racy issue between smb2 session log off and smb2 session setup. It will cause user-after-free from session log off. This add session_lock when setting SMB2_SESSION_EXPIRED and referece count to session struct not to free session while it is being used.
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Analysis
by VulDB Data Team • 08/21/2025
The vulnerability CVE-2024-50086 represents a critical race condition in the Linux kernel's ksmbd implementation that can lead to a user-after-free condition during SMB2 session management operations. This flaw specifically affects the ksmbd kernel module responsible for implementing SMB2/SMB3 protocol support in Linux systems, making it a significant security concern for network file sharing environments. The vulnerability arises from improper synchronization between session logoff and session setup operations, creating a window where memory management conflicts can occur.
The technical flaw manifests as a race condition between two concurrent operations within the SMB2 protocol implementation. When a session logoff operation occurs simultaneously with a session setup operation, the kernel fails to properly coordinate these competing access patterns to the same session data structures. This race condition allows for a scenario where a session structure can be freed from memory while another process is still accessing it, resulting in a user-after-free vulnerability. The vulnerability is classified under CWE-367 which specifically addresses Time-of-Check to Time-of-Use (TOCTOU) race conditions, and more broadly falls under CWE-416 which covers use-after-free conditions.
The operational impact of this vulnerability extends beyond simple memory corruption, as it can potentially enable arbitrary code execution or denial of service attacks. Attackers who can control the timing of session setup and logoff operations may exploit this race condition to corrupt kernel memory, leading to system instability or privilege escalation. The vulnerability affects systems running Linux kernels with ksmbd support, particularly those serving SMB2/SMB3 shares to remote clients. This makes it particularly dangerous in enterprise environments where file servers and network shares are heavily utilized, as the race condition can be triggered through normal network operations.
Mitigation strategies for CVE-2024-50086 focus on implementing proper synchronization mechanisms to prevent concurrent access to session structures during critical operations. The fix involves adding session_lock mechanisms when setting SMB2_SESSION_EXPIRED flags and maintaining proper reference counting for session structures to prevent premature deallocation. System administrators should prioritize applying the kernel patches that address this vulnerability, as they provide the necessary synchronization primitives to eliminate the race condition. Additionally, monitoring network traffic for unusual session management patterns and implementing network segmentation can help reduce the attack surface. Organizations should also consider disabling unnecessary SMB2/SMB3 services when not required and ensure regular kernel updates are deployed across all systems to maintain security posture. The vulnerability demonstrates the importance of proper concurrency control in kernel space operations and aligns with ATT&CK technique T1059.007 for kernel-mode rootkits, as it could potentially enable persistence mechanisms through memory corruption exploits.