CVE-2026-64453 Overview
CVE-2026-64453 is a use-after-free (UAF) vulnerability in the Linux kernel's usb: misc: usbio driver. The flaw resides in the usbio_disconnect() function, which iterates the client list in reverse to uninitialize each auxiliary device. When auxiliary_device_uninit() drops the final device reference on an unbound child, it invokes usbio_auxdev_release() and frees the containing struct usbio_client. The list_for_each_entry_reverse() iterator then dereferences the freed memory to advance to the previous element.
Critical Impact
A use-after-free during USB device disconnect can lead to kernel memory corruption, potentially resulting in privilege escalation or denial of service on affected Linux systems.
Affected Products
- Linux kernel versions containing the usbio USB misc driver prior to the fix
- Distributions shipping stable kernels referenced by commits 0bfeec21984f, 1947b6411460, and c40090f8d19b
- Systems that load the usbio auxiliary bus driver with attached client devices
Discovery Timeline
- 2026-07-25 - CVE-2026-64453 published to NVD
- 2026-07-25 - Last updated in NVD database
Technical Details for CVE-2026-64453
Vulnerability Analysis
The usbio_disconnect() function tears down auxiliary devices attached to a USB IO parent by traversing usbio->cli_list in reverse order. Each iteration calls auxiliary_device_uninit(), which decrements the device reference count. For an unbound child device, this reference drop is the final one and triggers usbio_auxdev_release(), freeing the struct usbio_client that contains the current list node.
The iteration uses list_for_each_entry_reverse(), which advances the cursor after the loop body executes by reading client->link.prev from the current entry. Because the current entry has already been freed, this pointer read dereferences slab memory that has been returned to the allocator. KASAN reports confirm this pattern as a slab-use-after-free in usbio_disconnect+0x12e/0x150.
Root Cause
The root cause is unsafe list iteration during object destruction. The list_for_each_entry_reverse() macro does not cache the next iterator position before the loop body runs, so any callee that frees the current element invalidates the iterator. The usbio driver violated this contract by allowing auxiliary_device_uninit() to release the containing client structure mid-iteration.
Attack Vector
Exploitation requires local access to trigger the disconnect path, typically through USB device removal or driver unbind operations. An attacker with the ability to attach and detach USB devices, or induce a probe failure that leads to disconnect, can force the vulnerable teardown path to execute. Successful exploitation corrupts kernel slab memory and may enable code execution in kernel context depending on heap layout and reallocation timing.
The vulnerability mechanism is described in the upstream commit messages linked from the Linux Kernel Git tree. No public proof-of-concept is available at this time.
Detection Methods for CVE-2026-64453
Indicators of Compromise
- KASAN reports containing slab-use-after-free in usbio_disconnect in kernel logs
- Unexpected kernel oopses or panics originating from usb_unbind_interface call paths involving the usbio module
- dmesg entries showing corruption warnings from the SLUB allocator following USB device disconnect events
Detection Strategies
- Enable KASAN on test kernels to surface use-after-free conditions in the usbio teardown path during QA cycles
- Audit loaded kernel modules with lsmod | grep usbio to identify hosts running the vulnerable driver
- Correlate USB hotplug events with kernel taint flag changes to identify potentially exploited hosts
Monitoring Recommendations
- Forward kernel ring buffer and journald logs to a centralized log platform for KASAN and oops pattern matching
- Monitor /proc/sys/kernel/tainted for state transitions on production Linux hosts
- Alert on repeated USB device attach and detach sequences from untrusted physical or virtualized USB sources
How to Mitigate CVE-2026-64453
Immediate Actions Required
- Update to a Linux stable kernel release that includes the fix commits 0bfeec21984f, 1947b6411460, or c40090f8d19b
- Restrict physical USB access on servers and workstations handling sensitive workloads
- Disable or blacklist the usbio module on systems that do not require it using /etc/modprobe.d/ configuration
Patch Information
The fix replaces list_for_each_entry_reverse() with list_for_each_entry_safe_reverse() in usbio_disconnect(). The safe variant caches the previous list entry before the loop body executes, so freeing the current client no longer corrupts the iterator. Patch details are available at the Linux Kernel Commit c40090f8, commit 0bfeec21, and commit 1947b641.
Workarounds
- Blacklist the usbio kernel module on hosts that do not require Intel USB IO bridge functionality
- Enforce USB device access policies via udev rules or USBGuard to prevent unauthorized attach and detach cycles
- Apply physical port controls and disable unused USB controllers in firmware for high-value systems
# Blacklist the vulnerable usbio module
echo "blacklist usbio" | sudo tee /etc/modprobe.d/blacklist-usbio.conf
sudo update-initramfs -u
sudo reboot
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
