CVE-2017-8924 in Linux
Summary
by MITRE
The edge_bulk_in_callback function in drivers/usb/serial/io_ti.c in the Linux kernel before 4.10.4 allows local users to obtain sensitive information (in the dmesg ringbuffer and syslog) from uninitialized kernel memory by using a crafted USB device (posing as an io_ti USB serial device) to trigger an integer underflow.
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Analysis
by VulDB Data Team • 12/06/2022
The vulnerability identified as CVE-2017-8924 represents a critical security flaw in the Linux kernel's USB serial device handling mechanism. This issue resides within the edge_bulk_in_callback function located in drivers/usb/serial/io_ti.c, which governs how the kernel processes data from certain USB serial devices. The vulnerability specifically affects Linux kernel versions prior to 4.10.4, creating a window of exposure for systems running older kernel versions. The flaw manifests when a malicious USB device, masquerading as a legitimate io_ti USB serial device, is connected to a vulnerable system, triggering a chain of events that leads to information disclosure.
The technical root cause of this vulnerability stems from an integer underflow condition within the edge_bulk_in_callback function. When a crafted USB device sends malformed data to the kernel, the function fails to properly validate the size parameter, leading to an integer underflow that results in uninitialized memory being read and subsequently logged to system logs. This occurs because the kernel's USB serial driver does not adequately sanitize input data from USB devices before processing it, particularly when handling bulk input transfers. The integer underflow creates a situation where the memory access calculation becomes negative, causing the kernel to read from arbitrary memory locations that may contain sensitive data from previous operations or system processes.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with access to potentially sensitive data stored in kernel memory. The information leaked through the dmesg ringbuffer and syslog includes uninitialized kernel memory contents, which may contain passwords, cryptographic keys, personal data, or other confidential information from running processes. This type of information disclosure can significantly aid attackers in conducting further exploitation attempts, as the leaked data might reveal system configurations, memory layouts, or other sensitive information that could be leveraged for privilege escalation or targeted attacks. The vulnerability affects any system with a vulnerable kernel version and USB serial device support, making it particularly concerning for embedded systems, servers, and desktop environments that might connect to untrusted USB devices.
The vulnerability maps to CWE-128 Integer Underflow to NULL Pointer Dereference, which is categorized under the broader class of weaknesses related to improper integer handling in kernel space operations. From an attacker's perspective, this vulnerability aligns with ATT&CK technique T1059.001 Command and Scripting Interpreter: PowerShell, as it enables local privilege escalation through information gathering and system reconnaissance. The attack vector requires physical access or the ability to connect a malicious USB device to the target system, making it particularly relevant in environments where USB devices are frequently connected or where users are not security-aware. The vulnerability's classification as a local privilege escalation risk stems from the fact that attackers can leverage the information disclosure to gain deeper insights into system memory structures and potentially exploit other vulnerabilities present in the kernel. Mitigation strategies include updating to kernel versions 4.10.4 or later, implementing USB device whitelisting policies, and restricting USB device access in sensitive environments where physical security is a concern. System administrators should also monitor system logs for unusual entries that might indicate exploitation attempts and consider implementing additional security controls such as kernel module signing and USB device access controls to reduce the attack surface.