CVE-2023-1989: Linux Kernel Use-After-Free Vulnerability

CVE-2023-1989 Overview

A use-after-free vulnerability was discovered in the Linux Kernel's Bluetooth SDIO driver, specifically in the btsdio_remove function located in drivers/bluetooth/btsdio.c. This flaw occurs when a call to btsdio_remove is made while an unfinished job is still in progress, creating a race condition that can lead to a use-after-free (UAF) condition on hdev devices.

Critical Impact

Local attackers with low privileges can exploit this race condition to potentially achieve privilege escalation, execute arbitrary code, or cause system instability through memory corruption.

Affected Products

• Linux Kernel (multiple versions)
• NetApp H300S, H410C, H410S, H500S, H700S storage systems
• Debian Linux 10.0 and 12.0

Discovery Timeline

• April 11, 2023 - CVE-2023-1989 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-1989

Vulnerability Analysis

This use-after-free vulnerability exists in the Bluetooth SDIO driver's device removal handling code. The core issue stems from improper synchronization between the device removal process and ongoing Bluetooth operations. When the btsdio_remove function is invoked, it attempts to clean up and deallocate the Bluetooth HCI device (hdev) structure. However, if there are pending or unfinished jobs referencing this device, the removal proceeds without proper synchronization, leaving dangling pointers.

The vulnerability is classified under CWE-416 (Use After Free), indicating that memory is accessed after it has been freed. In the context of kernel drivers, such vulnerabilities are particularly dangerous as they can lead to kernel-level code execution or system crashes.

Root Cause

The root cause lies in the lack of proper synchronization mechanisms within the btsdio_remove function. When the Bluetooth SDIO device is being removed, the function fails to ensure that all pending operations referencing the hdev structure have completed. This creates a time-of-check to time-of-use (TOCTOU) window where the memory can be freed while still being referenced by concurrent operations.

The race condition occurs because:

1. The removal function begins cleanup without acquiring appropriate locks
2. Concurrent Bluetooth operations may still hold references to the device
3. Memory is freed while these references remain active
4. Subsequent access to the freed memory triggers the use-after-free condition

Attack Vector

Exploitation of this vulnerability requires local access to the system. An attacker with low privileges could trigger the race condition by manipulating the timing of Bluetooth SDIO device removal operations. The attack complexity is considered high due to the need to win the race condition reliably.

A successful exploit could allow the attacker to corrupt kernel memory, potentially leading to privilege escalation, arbitrary code execution in kernel context, or denial of service through system crashes. The vulnerability affects systems with Bluetooth SDIO hardware where the vulnerable driver is loaded.

The exploitation mechanism involves carefully timing the device removal to coincide with ongoing Bluetooth operations, causing the kernel to access freed memory structures. This can be achieved through repeated triggering of device enumeration and removal cycles while maintaining active Bluetooth connections or operations.

Detection Methods for CVE-2023-1989

Indicators of Compromise

• Unexpected kernel crashes or panics with stack traces referencing btsdio_remove or Bluetooth HCI device structures
• System logs showing memory corruption errors related to Bluetooth subsystem operations
• Unusual Bluetooth device enumeration and removal activity patterns
• Kernel OOPS messages indicating invalid memory access in Bluetooth driver code

Detection Strategies

• Monitor kernel logs for KASAN (Kernel Address Sanitizer) reports identifying use-after-free conditions in Bluetooth drivers
• Implement runtime kernel integrity monitoring to detect unexpected memory access patterns
• Deploy endpoint detection solutions capable of identifying kernel-level exploitation attempts
• Review audit logs for suspicious user activity involving Bluetooth device manipulation

Monitoring Recommendations

• Enable kernel debugging features such as KASAN and KMSAN in development and testing environments
• Configure syslog aggregation to centrally monitor for Bluetooth-related kernel errors across fleet
• Implement alerting for repeated Bluetooth device connection/disconnection events
• Monitor for processes attempting to load or unload Bluetooth kernel modules with elevated privileges

How to Mitigate CVE-2023-1989

Immediate Actions Required

• Apply the latest kernel security patches from your Linux distribution immediately
• Review systems for Bluetooth SDIO hardware usage and prioritize patching those systems
• Consider disabling Bluetooth functionality on critical systems where it is not required until patches are applied
• Monitor affected systems for signs of exploitation attempts

Patch Information

The vulnerability has been addressed through a patch committed to the Linux Bluetooth subsystem. The fix is available in the Linux Bluetooth kernel commit f132c2d13088. Distribution-specific patches are available:

• Debian Security Advisory DSA-5492
• Debian LTS Announcements for older releases
• NetApp Security Advisory NTAP-20230601-0004 for affected storage systems

Workarounds

• Disable Bluetooth SDIO support by blacklisting the btsdio kernel module if Bluetooth functionality is not required
• Restrict physical access to systems with Bluetooth hardware to reduce attack surface
• Implement strict user access controls to limit which users can interact with Bluetooth devices
• Consider using alternative Bluetooth drivers or USB-based Bluetooth adapters where SDIO is not necessary

# Disable btsdio kernel module to mitigate vulnerability
echo "blacklist btsdio" | sudo tee /etc/modprobe.d/disable-btsdio.conf
sudo update-initramfs -u
sudo reboot