CVE-2025-71082: Linux Kernel Use-After-Free Vulnerability

CVE-2025-71082 Overview

CVE-2025-71082 is a Use-After-Free vulnerability in the Linux kernel's Bluetooth btusb driver. The vulnerability exists in the btusb_probe() function where devm_kzalloc() is used to allocate btusb data, creating a memory management issue when the driver binds to multiple interfaces (INTF, ISOC, and DIAG). This improper memory lifecycle management can lead to use-after-free conditions when interfaces are released in btusb_disconnect().

Critical Impact

When usb_driver_release_interface() is called during disconnect, it triggers devm to free memory that may still be in use by other interfaces, potentially leading to memory corruption or system instability.

Affected Products

• Linux kernel with btusb Bluetooth driver
• Systems using USB Bluetooth adapters with the btusb driver
• Linux distributions with affected kernel versions

Discovery Timeline

• 2026-01-13 - CVE CVE-2025-71082 published to NVD
• 2026-01-13 - Last updated in NVD database

Technical Details for CVE-2025-71082

Vulnerability Analysis

This vulnerability stems from improper memory management in the btusb Bluetooth driver. The driver uses devm_kzalloc() for memory allocation, which ties the lifetime of allocated memory to the binding of a driver to a single interface. However, the btusb driver binds to multiple USB interfaces: the main interface (INTF), the isochronous interface (ISOC), and the diagnostic interface (DIAG).

The fundamental issue occurs during the disconnect sequence. When btusb_disconnect() calls usb_driver_release_interface(&btusb_driver, data->intf), the devm framework frees the btusb data structure. However, the other interfaces (ISOC and DIAG) may still hold references to this memory, leading to a classic use-after-free condition where freed memory is accessed by still-active interfaces.

Root Cause

The root cause is the inappropriate use of device-managed memory allocation (devm_kzalloc()) in a multi-interface driver context. The devm subsystem automatically frees allocated memory when the associated device is unbound, but this behavior conflicts with the btusb driver's architecture where a single data structure is shared across multiple interfaces with different lifecycles. The original commit 98921dbd00c4e introduced this problematic change to use devm for memory management without accounting for the multi-interface binding model.

Attack Vector

The vulnerability is triggered through normal USB device disconnect operations or interface release sequences. An attacker with local access could potentially exploit this by manipulating Bluetooth device connections and disconnections to trigger the use-after-free condition. The exploitation requires:

1. A system with an active btusb driver binding
2. The ability to trigger interface disconnect operations in a specific sequence
3. Timing manipulation to access freed memory before it's reallocated

The vulnerability manifests in the btusb_disconnect() function when interface release operations free shared data structures prematurely. For detailed technical analysis, refer to the kernel git commits which revert to explicit memory management to resolve this issue.

Detection Methods for CVE-2025-71082

Indicators of Compromise

• Kernel panic or oops messages referencing btusb driver functions
• Memory corruption warnings in kernel logs related to Bluetooth subsystem
• System instability when disconnecting USB Bluetooth devices
• Kernel KASAN (Kernel Address Sanitizer) reports indicating use-after-free in btusb

Detection Strategies

• Monitor kernel logs for btusb-related memory errors or NULL pointer dereferences
• Enable KASAN in kernel builds to detect use-after-free conditions during testing
• Review system logs for unexpected Bluetooth driver failures during USB disconnect events
• Implement kernel debugging features to trace btusb memory allocations and deallocations

Monitoring Recommendations

• Deploy kernel live patching solutions to monitor and protect against btusb memory issues
• Configure syslog monitoring for btusb-related kernel warnings and errors
• Utilize SentinelOne Singularity platform for real-time kernel-level threat detection
• Monitor dmesg output for Bluetooth subsystem anomalies during device operations

How to Mitigate CVE-2025-71082

Immediate Actions Required

• Update to a patched Linux kernel version containing the fix commits
• Review and apply kernel patches from the stable kernel tree
• Consider temporarily disabling USB Bluetooth devices on critical systems until patched
• Monitor systems for signs of exploitation attempts through kernel log analysis

Patch Information

The Linux kernel maintainers have released patches that revert the problematic devm_kzalloc() usage and restore explicit memory management in the btusb driver. Multiple patch commits are available across kernel stable branches:

• Kernel Git Commit 1e54c19
• Kernel Git Commit 252714f
• Kernel Git Commit c0ecb3e
• Kernel Git Commit cca0e92
• Kernel Git Commit fdf7c64

Workarounds

• Blacklist the btusb module on systems where Bluetooth is not required: add blacklist btusb to /etc/modprobe.d/blacklist.conf
• Disable Bluetooth service and unload btusb module using systemctl stop bluetooth && rmmod btusb
• Use external Bluetooth dongles with alternative drivers if available
• Implement access controls to prevent unauthorized USB device connections

# Disable btusb module as a temporary workaround
echo "blacklist btusb" >> /etc/modprobe.d/btusb-blacklist.conf
modprobe -r btusb
systemctl stop bluetooth