CVE-2011-1771 in Linux
Summary
by MITRE
The cifs_close function in fs/cifs/file.c in the Linux kernel before 2.6.39 allows local users to cause a denial of service (NULL pointer dereference and BUG) or possibly have unspecified other impact by setting the O_DIRECT flag during an attempt to open a file on a CIFS filesystem.
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Analysis
by VulDB Data Team • 11/18/2021
The vulnerability identified as CVE-2011-1771 represents a critical flaw in the Linux kernel's CIFS (Common Internet File System) implementation that affects systems running kernel versions prior to 2.6.39. This issue resides within the cifs_close function located in fs/cifs/file.c, which handles file operations on CIFS filesystems. The vulnerability manifests when local users exploit the O_DIRECT flag during file open operations, creating a scenario that can lead to system instability and potential security implications. The CIFS protocol implementation in Linux enables mounting network shares from Windows servers and other CIFS-compatible systems, making this vulnerability particularly concerning for enterprise environments that rely heavily on network file sharing.
The technical root cause of this vulnerability stems from inadequate input validation and error handling within the cifs_close function. When the O_DIRECT flag is set during file operations, the kernel's CIFS driver fails to properly validate the file handle state before attempting to close the file. This leads to a NULL pointer dereference condition where the system attempts to access memory at address zero, triggering a kernel BUG message and ultimately causing a system crash or denial of service. The flaw demonstrates poor defensive programming practices and highlights the importance of proper resource management in kernel space operations. According to CWE-476, this vulnerability maps to NULL pointer dereference, a common weakness that can result in system instability and potential privilege escalation scenarios.
The operational impact of CVE-2011-1771 extends beyond simple denial of service, as local attackers with basic system access can exploit this vulnerability to disrupt normal system operations. In enterprise environments where CIFS mounts are commonly used for shared resources, this vulnerability could be leveraged to create persistent service disruptions or potentially enable more sophisticated attacks if combined with other exploits. The vulnerability affects systems that utilize CIFS filesystems, which are prevalent in corporate networks where Windows file servers are commonly accessed from Linux clients. Attackers could potentially use this vulnerability to exhaust system resources or cause repeated crashes, leading to availability issues that impact business operations and user productivity.
Mitigation strategies for this vulnerability primarily focus on kernel version upgrades to 2.6.39 or later, where the issue has been resolved through proper input validation and error handling mechanisms. System administrators should prioritize patching affected systems, particularly those running older kernel versions that continue to be used in production environments. Additionally, implementing proper access controls and limiting local user privileges can reduce the attack surface for this vulnerability. Organizations should also consider monitoring for unusual system behavior or frequent crashes that might indicate exploitation attempts. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving privilege escalation and denial of service, though it specifically targets the kernel level rather than user-space applications. The vulnerability demonstrates the critical importance of kernel security hardening and proper code review processes for system-level components that handle network protocols and file operations.