CVE-2026-43324: Linux Kernel Race Condition Vulnerability

CVE-2026-43324 Overview

CVE-2026-43324 is a kernel-level synchronization flaw in the Linux dummy-hcd USB Host Controller Driver. The driver emulates a USB host controller for testing USB gadget drivers without real hardware. The vulnerability stems from incorrect ordering of the emulated synchronize_irq() call relative to the emulated interrupt-disable operation. As a result, callback handlers can still execute after synchronization has completed, leading to a race condition when a gadget driver is unbound. A local, low-privileged attacker on a system with dummy-hcd loaded can exploit this race to achieve memory corruption or escalation of privilege.

Critical Impact
Local attackers can trigger a race condition between emulated USB interrupt callbacks and gadget driver unbind, potentially leading to use-after-free and local privilege escalation on affected Linux kernels.

Affected Products

Linux Kernel (multiple stable branches prior to fix)
Linux Kernel 7.0-rc1 through 7.0-rc7 release candidates
Distributions shipping the dummy-hcd USB gadget testing driver

Discovery Timeline

2026-05-08 - CVE-2026-43324 published to NVD
2026-05-15 - Last updated in NVD database

Technical Details for CVE-2026-43324

Vulnerability Analysis

The flaw resides in the dummy-hcd driver, which emulates USB host controller behavior for gadget driver testing. The driver implements an emulated "interrupts enabled" flag plus an emulated synchronize_irq() that waits until in-flight handler callbacks return. The synchronization mechanism has been revised multiple times, but the current state still misorders two operations. The emulated synchronize_irq() runs before the emulated interrupt-disable. This means new emulated interrupts can fire after synchronization completes. A callback handler may then execute while the gadget driver is being unbound, producing a use-after-free or invalid-state condition.

The fix moves the synchronize_irq() emulation into the dummy_udc_async_callbacks() routine. This routine is responsible for enabling and disabling emulated interrupt requests, so synchronization runs immediately after interrupts are disabled, eliminating the window.

Root Cause

The root cause is an ordering bug in the lifecycle management of emulated interrupts. Prior commits — 7dbd8f4cabd9, 4a5d797a9f9c, 7dc0c55e9f30, and 04145a03db9d — attempted incremental fixes by adding the udc_async_callbacks gadget operation. None placed the synchronization barrier after the disable step. The result is a classic race condition [CWE-362] between interrupt teardown and driver unbind.

Attack Vector

Exploitation requires local code execution and the ability to load or interact with the dummy-hcd driver and an attached gadget driver. An attacker triggers repeated bind and unbind cycles of a gadget driver while emulated USB activity is in flight. By winning the race, the attacker causes a callback to dereference structures freed during unbind. This can be leveraged to corrupt kernel memory and escalate privileges from an unprivileged local account to root.

No public exploit code is available for CVE-2026-43324, and the CVE is not listed in the CISA Known Exploited Vulnerabilities catalog.

Detection Methods for CVE-2026-43324

Indicators of Compromise

Unexpected kernel oops, panic, or KASAN use-after-free reports referencing dummy_hcd, dummy_udc, or gadget_setup call sites.
Repeated module bind and unbind activity on dummy_hcd or attached gadget drivers from non-root processes.
Kernel log entries showing gadget driver callbacks executing after unbind notification.

Detection Strategies

Inventory running kernel versions against the patched commits (2ca9e46f, 5687a097, 5aa776c8, 8bcd8021, 94d4fab1, cbf7df5e, d847f375) and flag systems still on vulnerable builds.
Monitor auditd for init_module, finit_module, and delete_module syscalls targeting dummy_hcd and USB gadget modules from unexpected users.
Enable KASAN and lockdep in test environments to surface the race during continuous integration.

Monitoring Recommendations

Forward kernel ring buffer logs (dmesg, journald) to a central SIEM and alert on USB gadget subsystem stack traces.
Track process activity that loads kernel modules outside of approved configuration management workflows.
Baseline expected usage of dummy-hcd (typically only on developer or test systems) and alert on its presence in production.

How to Mitigate CVE-2026-43324

Immediate Actions Required

Apply the upstream kernel patches that move synchronize_irq() emulation into dummy_udc_async_callbacks(), available across the stable trees.
On production systems that do not require USB gadget testing, blacklist or remove the dummy_hcd module to eliminate the attack surface.
Restrict module loading to root and enable kernel lockdown where supported, preventing low-privileged users from loading dummy_hcd.

Patch Information

Fixes are available in the mainline and stable Linux kernel trees. See the upstream commits: Kernel Patch 2ca9e46, Kernel Patch 5687a09, Kernel Patch 5aa776c, Kernel Patch 8bcd802, Kernel Patch 94d4fab, Kernel Patch cbf7df5, and Kernel Patch d847f37. Rebuild and reboot affected hosts after applying distribution updates.

Workarounds

Blacklist the dummy_hcd module via /etc/modprobe.d/ to prevent it from loading on systems that do not require USB gadget emulation.
Set kernel.modules_disabled=1 after boot on systems with a fixed module set to prevent runtime loading of vulnerable modules.
Apply Mandatory Access Control policies (SELinux, AppArmor) that deny non-root users access to /dev/usb-ffs and USB gadget configfs paths.

bash

# Configuration example
echo 'blacklist dummy_hcd' | sudo tee /etc/modprobe.d/disable-dummy-hcd.conf
echo 'install dummy_hcd /bin/true' | sudo tee -a /etc/modprobe.d/disable-dummy-hcd.conf
sudo rmmod dummy_hcd 2>/dev/null || true
sudo update-initramfs -u