CVE-2017-18079 in Linux
Summary
by MITRE
drivers/input/serio/i8042.c in the Linux kernel before 4.12.4 allows attackers to cause a denial of service (NULL pointer dereference and system crash) or possibly have unspecified other impact because the port->exists value can change after it is validated.
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Analysis
by VulDB Data Team • 02/03/2023
The vulnerability identified as CVE-2017-18079 resides within the Linux kernel's input subsystem, specifically in the i8042.c driver responsible for handling PS/2 keyboard and mouse controllers. This flaw represents a classic race condition vulnerability that occurs when the driver fails to maintain consistent state validation throughout its execution cycle. The vulnerability affects Linux kernel versions prior to 4.12.4 and demonstrates how improper state management can lead to system instability. The core issue manifests when the driver validates the existence of a serial port through the port->exists parameter but subsequently allows this value to change before the validation is fully utilized, creating a window where the system operates on stale state information.
The technical exploitation of this vulnerability stems from a race condition between the validation of port existence and the actual execution of port operations. When the i8042 driver checks if a port exists and proceeds with operations based on that validation, an external factor can modify the port->exists value between the check and the operation execution. This condition creates a NULL pointer dereference scenario where the driver attempts to access memory locations that may no longer be valid or accessible. The vulnerability is categorized under CWE-362, which describes a race condition that allows multiple threads or processes to access shared resources simultaneously, leading to unpredictable behavior. The timing aspect of this vulnerability makes it particularly challenging to exploit consistently, as it requires precise coordination with system events that might alter the port state during the validation window.
The operational impact of CVE-2017-18079 extends beyond simple denial of service to potentially enable more sophisticated attacks. A successful exploitation can result in complete system crashes through NULL pointer dereferences, forcing system administrators to reboot affected machines and potentially disrupting critical services. In environments where system stability is paramount, such as enterprise servers or embedded systems, this vulnerability can lead to significant operational downtime and service interruptions. The unspecified other impacts mentioned in the vulnerability description suggest that under certain conditions, attackers might be able to leverage this flaw for privilege escalation or information disclosure, though these scenarios require additional exploitation vectors. The vulnerability aligns with ATT&CK technique T1499.001, which covers network denial of service attacks, and represents a critical weakness in the kernel's input handling subsystem that can be exploited by attackers with minimal privileges.
Mitigation strategies for CVE-2017-18079 primarily involve upgrading to Linux kernel version 4.12.4 or later, where the race condition has been resolved through proper synchronization mechanisms. System administrators should implement comprehensive patch management processes to ensure all affected systems receive timely updates. Additionally, monitoring for unusual system crashes or reboot patterns can help identify potential exploitation attempts. The fix implemented in the patched kernel version addresses the root cause by ensuring that port state validation remains consistent throughout the execution cycle, preventing the race condition that led to the NULL pointer dereference. Organizations should also consider implementing kernel hardening measures such as stack canaries and address space layout randomization to further reduce the attack surface. The vulnerability highlights the importance of proper synchronization in kernel drivers and demonstrates how seemingly minor state management issues can result in critical system instability, making it a prime example of why kernel security reviews and formal verification techniques are essential for maintaining system integrity.