CVE-2024-49988 in Linux
Summary
by MITRE • 10/21/2024
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: add refcnt to ksmbd_conn struct
When sending an oplock break request, opinfo->conn is used, But freed ->conn can be used on multichannel. This patch add a reference count to the ksmbd_conn struct so that it can be freed when it is no longer used.
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Analysis
by VulDB Data Team • 03/21/2026
The vulnerability identified as CVE-2024-49988 affects the Linux kernel's ksmbd implementation, which provides SMB/CIFS file sharing capabilities for Linux systems. This issue specifically targets the handling of connection references during oplock break operations, creating a potential race condition that could lead to system instability or security implications. The ksmbd subsystem serves as a kernel module that enables Linux servers to function as SMB/CIFS file servers, making it a critical component for enterprise file sharing environments and network infrastructure.
The technical flaw stems from improper reference counting within the ksmbd_conn structure during oplock break processing. When an oplock break request is sent, the system accesses opinfo->conn which may have already been freed in multichannel scenarios. This occurs because the connection reference count is not properly maintained, allowing the kernel to access memory that has already been deallocated. The vulnerability manifests when multiple channels are involved in SMB operations, where connection cleanup and reference management become complex due to concurrent access patterns. This type of memory management error falls under the CWE-415: Double Free category, though more specifically represents a use-after-free condition that can result in arbitrary code execution or system crashes.
The operational impact of this vulnerability is significant for systems running ksmbd as their primary SMB server implementation. An attacker who can trigger the specific sequence leading to the use-after-free condition could potentially cause system crashes, leading to denial of service, or in more sophisticated scenarios, achieve privilege escalation or arbitrary code execution. The vulnerability is particularly concerning in enterprise environments where ksmbd is used for file sharing, as it could be exploited to disrupt critical business operations. The multichannel nature of the vulnerability means that it affects systems handling concurrent SMB connections, which are common in high-availability and clustered environments. According to ATT&CK framework, this vulnerability could be leveraged under technique T1499.004: Endpoint Denial of Service, or potentially T1068: Exploitation for Privilege Escalation if proper access controls are bypassed.
The patch addressing this vulnerability implements proper reference counting for the ksmbd_conn structure, ensuring that connections remain valid while they are actively being used in oplock break operations. This fix prevents the use of freed memory by maintaining a reference count that prevents deallocation until all operations referencing the connection are complete. The solution aligns with standard kernel security practices for managing object lifecycles in concurrent environments, where proper reference counting is essential to prevent use-after-free vulnerabilities. Organizations should prioritize applying this patch to all systems running ksmbd, particularly those serving as SMB file servers in production environments. The mitigation strategy also includes monitoring for unusual connection patterns or system crashes that might indicate exploitation attempts, while ensuring proper system updates are maintained to address similar vulnerabilities in the broader kernel ecosystem.