CVE-2019-15917 in Linux
Summary
by MITRE
An issue was discovered in the Linux kernel before 5.0.5. There is a use-after-free issue when hci_uart_register_dev() fails in hci_uart_set_proto() in drivers/bluetooth/hci_ldisc.c.
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Analysis
by VulDB Data Team • 12/11/2023
The vulnerability identified as CVE-2019-15917 represents a critical use-after-free flaw in the Linux kernel's Bluetooth subsystem that affects versions prior to 5.0.5. This issue resides within the HCI (Host Controller Interface) line discipline implementation specifically in the drivers/bluetooth/hci_ldisc.c file. The vulnerability manifests when the hci_uart_register_dev() function fails during the hci_uart_set_proto() execution sequence, creating a scenario where memory that has been freed is subsequently accessed, leading to potential system instability or arbitrary code execution.
The technical root cause of this vulnerability aligns with CWE-416, which defines use-after-free conditions as a common class of memory safety issues. When hci_uart_set_proto() encounters a failure in hci_uart_register_dev(), the code path does not properly handle the cleanup of previously allocated resources, leaving pointers in a state where they reference freed memory locations. This memory management error occurs in the context of Bluetooth UART communication protocols where the kernel attempts to establish and configure serial communication channels for Bluetooth devices. The flaw specifically impacts the HCI line discipline layer that manages the serial interface between Bluetooth host controllers and the kernel's Bluetooth subsystem, making it particularly dangerous for systems that rely on Bluetooth connectivity.
The operational impact of this vulnerability extends beyond simple system crashes, as it creates potential attack vectors for privilege escalation and system compromise. An attacker with local access or the ability to trigger the specific failure condition could exploit this vulnerability to execute arbitrary code with kernel privileges, effectively gaining complete control over the affected system. The nature of the Bluetooth subsystem means that this vulnerability could be exploited in various scenarios including mobile devices, servers, and embedded systems that utilize Bluetooth connectivity. The vulnerability's exploitation potential is further amplified by its location in the kernel's core Bluetooth handling code, which is frequently accessed during normal system operation when Bluetooth devices are connected or configured.
Mitigation strategies for CVE-2019-15917 primarily focus on kernel version upgrades to 5.0.5 or later where the vulnerability has been patched. System administrators should prioritize updating their kernel versions, particularly in production environments where Bluetooth functionality is utilized. Additionally, implementing proper access controls and network segmentation can help limit the potential attack surface, though these measures do not address the underlying memory safety issue. The fix implemented in the patched kernel versions involves proper resource cleanup and error handling within the hci_uart_set_proto() function to ensure that all allocated memory is properly managed even when hci_uart_register_dev() fails. Organizations should also consider monitoring for suspicious Bluetooth-related activities and implementing security controls that align with the MITRE ATT&CK framework's privilege escalation and defense evasion techniques, as this vulnerability could be leveraged to establish persistent access to compromised systems.