CVE-2015-7515 in Linux
Summary
by MITRE
The aiptek_probe function in drivers/input/tablet/aiptek.c in the Linux kernel before 4.4 allows physically proximate attackers to cause a denial of service (NULL pointer dereference and system crash) via a crafted USB device that lacks endpoints.
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Analysis
by VulDB Data Team • 11/04/2024
The vulnerability identified as CVE-2015-7515 resides within the Linux kernel's input subsystem, specifically in the aiptek_probe function located in drivers/input/tablet/aiptek.c. This flaw represents a classic null pointer dereference issue that can be exploited by attackers who are physically proximate to the target system. The vulnerability affects Linux kernel versions prior to 4.4, making it a significant concern for systems that have not been updated to newer kernel releases. The issue manifests when a crafted USB device is connected that lacks proper endpoint configuration, which is a common scenario in malicious USB device attacks.
The technical implementation of this vulnerability stems from inadequate input validation within the aiptek_probe function, which is responsible for initializing USB tablet devices manufactured by Aiptek. When a USB device is connected, the kernel attempts to probe and initialize the device by examining its endpoint descriptors. However, the function fails to properly check whether the device has valid endpoint configurations before attempting to access them. This oversight creates a condition where the kernel dereferences a NULL pointer when processing a device that lacks the expected endpoint structure, leading to an immediate system crash.
The operational impact of this vulnerability extends beyond simple denial of service, as it can be leveraged by attackers to disrupt system operations in a manner that aligns with the MITRE ATT&CK framework's privilege escalation and denial of service tactics. An attacker positioned within physical proximity to a target system can connect a malicious USB device that mimics legitimate tablet hardware but omits critical endpoint information. This attack vector is particularly concerning because it bypasses traditional network-based security controls and relies on physical access or social engineering to gain initial system presence. The vulnerability can be classified under CWE-476 as a NULL pointer dereference, representing a fundamental flaw in pointer validation that has been present in the kernel's USB input handling code for an extended period.
Systems running affected kernel versions are vulnerable to complete system crashes that can result in data loss, service interruption, and potential compromise of system integrity. The attack requires minimal sophistication to execute and can be automated through malicious USB devices that are increasingly available in commercial markets. Organizations should prioritize kernel updates to address this vulnerability, as the patch implemented in kernel version 4.4 correctly validates endpoint structures before attempting to access them. Additional mitigations include implementing USB device whitelisting policies, disabling unnecessary USB ports, and deploying physical security controls to prevent unauthorized device insertion. The vulnerability also highlights the importance of proper input validation in kernel space code, emphasizing the need for comprehensive testing of device initialization routines and adherence to secure coding practices as outlined in industry security standards and best practices.