CVE-2011-5321 in Linux
Summary
by MITRE
The tty_open function in drivers/tty/tty_io.c in the Linux kernel before 3.1.1 mishandles a driver-lookup failure, which allows local users to cause a denial of service (NULL pointer dereference and system crash) or possibly have unspecified other impact via crafted access to a device file under the /dev/pts directory.
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Analysis
by VulDB Data Team • 04/15/2022
The vulnerability identified as CVE-2011-5321 represents a critical flaw in the Linux kernel's terminal I/O subsystem that affects versions prior to 3.1.1. This issue resides within the tty_open function located in drivers/tty/tty_io.c, which is responsible for managing terminal device operations. The vulnerability stems from improper handling of driver lookup failures during terminal device initialization, creating a scenario where malicious local users can exploit this weakness to disrupt system operations. The flaw specifically manifests when a device file under the /dev/pts directory is accessed with crafted parameters, leading to unpredictable system behavior that can compromise overall system stability.
The technical implementation of this vulnerability involves a NULL pointer dereference condition that occurs during the driver lookup process within the tty_open function. When the kernel attempts to locate an appropriate driver for a terminal device but fails to find one, the function does not properly validate the lookup result before proceeding with operations that assume a valid driver reference exists. This failure to check for NULL return values from driver lookup functions creates a path where subsequent operations attempt to dereference a null pointer, resulting in immediate system crashes. The underlying CWE classification for this issue aligns with CWE-476 which addresses NULL pointer dereference vulnerabilities, and the attack pattern corresponds to privilege escalation through system resource manipulation.
From an operational impact perspective, this vulnerability enables local users to achieve both denial of service conditions and potentially more severe consequences depending on system configuration and access levels. The immediate effect of a successful exploitation is a system crash that forces the kernel to panic and potentially reboot the entire system, rendering services unavailable and potentially causing data loss. The unspecified other impacts mentioned in the description suggest that under certain conditions, this vulnerability might provide opportunities for privilege escalation or information disclosure, though the primary threat remains system instability. The /dev/pts directory serves as a critical interface for pseudo-terminal devices used by various applications including shells, terminal emulators, and remote access tools, making this vulnerability particularly dangerous in multi-user environments.
The exploitation of this vulnerability requires local system access and leverages the inherent trust relationships within the terminal subsystem. Attackers typically craft specific device access patterns that trigger the driver lookup failure condition, often involving malformed device file operations or attempts to access non-existent terminal devices. The ATT&CK framework categorizes this vulnerability under privilege escalation techniques, specifically targeting the kernel-level system calls that manage device access and resource allocation. Mitigation strategies include applying the kernel patch released with version 3.1.1 which properly handles driver lookup failures by implementing appropriate NULL checks before proceeding with device initialization operations. System administrators should also consider implementing additional monitoring and logging around terminal device access patterns to detect potential exploitation attempts, and maintain current kernel versions to prevent exploitation of known vulnerabilities.