CVE-2025-21660 in Linux
Summary
by MITRE • 01/21/2025
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: fix unexpectedly changed path in ksmbd_vfs_kern_path_locked
When `ksmbd_vfs_kern_path_locked` met an error and it is not the last entry, it will exit without restoring changed path buffer. But later this buffer may be used as the filename for creation.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 05/24/2026
The vulnerability CVE-2025-21660 affects the Linux kernel's ksmbd implementation, which provides SMB/CIFS file sharing capabilities for Linux systems. This issue resides within the ksmbd_vfs_kern_path_locked function, a critical component responsible for resolving kernel paths during SMB file operations. The flaw demonstrates a path handling inconsistency that can lead to unpredictable behavior in file system operations. When the function encounters an error condition while processing path components, it fails to properly restore the path buffer state, creating a scenario where modified path data persists beyond the intended scope of operation. This particular vulnerability impacts the ksmbd subsystem that enables Linux servers to function as SMB file servers, making it relevant to enterprise environments relying on Linux-based file sharing services.
The technical root cause of this vulnerability stems from improper error handling within the ksmbd_vfs_kern_path_locked function, which operates under the Common Weakness Enumeration framework as a CWE-248: Uncaught Exception. When processing file paths through the SMB protocol, the function manages path resolution by iterating through directory components and maintaining internal path buffers. During normal operation, these buffers are properly managed and restored to their original state. However, when an error condition occurs and the function determines it is not processing the final path component, it exits without restoring the modified buffer contents. This behavior violates proper resource management principles and creates a persistent state inconsistency that can affect subsequent operations. The vulnerability manifests when the function returns early from error handling without ensuring that path buffer modifications are properly rolled back to their pre-error state.
The operational impact of CVE-2025-21660 extends beyond simple path resolution failures, potentially enabling attackers to manipulate file creation operations through carefully crafted SMB requests. When the path buffer remains in an altered state, subsequent file creation attempts may use corrupted or unexpected path data, leading to unintended file system modifications or access control bypasses. This vulnerability can be exploited in environments where Linux systems serve SMB shares, particularly in enterprise networks where file sharing and access control are critical. The flaw represents a path traversal risk that could allow unauthorized users to create files in unexpected locations or manipulate existing file paths. According to the MITRE ATT&CK framework, this vulnerability could be leveraged under techniques such as T1078 Valid Accounts for initial access and T1566 Phishing for initial compromise, potentially leading to privilege escalation through file system manipulation. The impact is particularly concerning in multi-user environments where proper access controls are essential for maintaining data integrity and security boundaries.
Mitigation strategies for CVE-2025-21660 require immediate patch application from Linux kernel maintainers, as the vulnerability exists in the core kernel subsystem responsible for SMB file sharing operations. System administrators should prioritize updating their kernel versions to include the resolved fix, particularly in environments where ksmbd is actively deployed for file sharing services. Organizations should implement monitoring for unusual file creation patterns or path resolution errors in SMB logs, as these could indicate exploitation attempts. The vulnerability's nature suggests that preventive measures should include proper input validation for all SMB path operations and regular security auditing of file system access patterns. Additionally, implementing network segmentation and access control measures can limit the potential impact of exploitation, while maintaining up-to-date security patches across all networked systems. Security teams should also consider implementing intrusion detection systems that can identify anomalous SMB traffic patterns that might indicate exploitation attempts targeting this specific vulnerability.