CVE-2026-64363 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
HID: appleir: fix UAF on pending key_up_timer in remove()
appleir_remove() runs hid_hw_stop() before timer_delete_sync(). hid_hw_stop() synchronously unregisters the HID input device via hid_disconnect() -> hidinput_disconnect() -> input_unregister_device(), which drops the last reference and frees the underlying input_dev when no userspace handle holds it open.
key_up_tick() reads appleir->input_dev and calls input_report_key() / input_sync() on it. The timer is armed from appleir_raw_event() with a HZ/8 (~125 ms) timeout on every keydown and key-repeat report. If a key was pressed shortly before the device is disconnected, the timer can fire after hid_hw_stop() has freed input_dev but before the teardown drains it.
A simple reorder is not sufficient. Putting the timer drain first still leaves a window where a USB URB completion (raw_event) running during hid_hw_stop() can call mod_timer() and re-arm the timer, which then fires after hidinput_disconnect() has freed input_dev. The same URB-completion window also lets raw_event() reach key_up(), key_down() and battery_flat() directly, all of which dereference appleir->input_dev.
Introduce a 'removing' flag on struct appleir, gated by the existing spinlock. appleir_remove() sets the flag under the lock and then shuts down the timer with timer_shutdown_sync(), which both drains any in-flight callback and permanently disables further mod_timer() calls. appleir_raw_event() and key_up_tick() bail out early if the flag is set, so no path can arm or run the timer, or dereference appleir->input_dev, after remove() has started tearing down.
The keyrepeat and flatbattery branches of appleir_raw_event() previously called into the input layer without holding the spinlock; take it now so the flag check is well-defined. This incidentally closes a pre-existing read-side race on appleir->current_key in the keyrepeat branch.
This bug is structurally a sibling of commit 4db2af929279 ("HID: appletb-kbd: fix UAF in inactivity-timer cleanup path") and has been present since the driver was introduced.
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Analysis
by VulDB Data Team • 07/25/2026
The vulnerability described represents a use-after-free condition affecting the appleir HID driver within the Linux kernel, specifically manifesting during device removal operations. This issue arises from improper synchronization between the timer management and device teardown processes, creating a window where asynchronous operations can access freed memory structures. The problem is particularly concerning as it occurs in a kernel module responsible for handling input devices from Apple's infrared remote control hardware, potentially leading to system instability or privilege escalation if exploited by malicious actors.
The technical flaw stems from the sequence of operations in the appleir_remove() function where hid_hw_stop() is invoked before timer_delete_sync(). The hid_hw_stop() function performs a synchronous HID device unregister via hid_disconnect() -> hidinput_disconnect() -> input_unregister_device(), which ultimately drops the last reference to the input device and frees the underlying input_dev structure. However, the key_up_timer can still fire after this freeing process has begun but before all pending operations have completed, creating a race condition where key_up_tick() attempts to access the freed input_dev structure through input_report_key() and input_sync() calls.
The vulnerability's complexity increases due to the presence of multiple concurrent execution paths that can access the freed device structure. USB URB completions running during hid_hw_stop() can still call mod_timer() to re-arm the timer, creating another window where the timer fires after input_dev has been freed. Additionally, raw_event() operations can directly invoke key_up(), key_down(), and battery_flat() functions that all dereference appleir->input_dev, making the race condition even more pervasive across different code paths within the driver.
The proposed solution implements a 'removing' flag within the appleir structure to provide proper synchronization during device removal. This flag is managed under the existing spinlock to ensure atomic access and prevents any further timer modifications or callbacks once the removal process begins. The approach involves setting the flag before shutting down the timer with timer_shutdown_sync(), which not only drains in-flight callbacks but also permanently disables future mod_timer() calls. This prevents all potential code paths from accessing freed memory structures even if they execute concurrently with the removal process.
The fix also addresses additional race conditions present in the original implementation by ensuring proper locking around access to shared data structures during keyrepeat and flatbattery processing branches. Previously, these branches called into the input layer without holding the spinlock, creating read-side races on appleir->current_key in the keyrepeat branch. The updated implementation now acquires the spinlock before accessing shared data, making all flag checks well-defined and eliminating pre-existing race conditions that could have contributed to system instability.
This vulnerability aligns with common security patterns identified by CWE 416, which addresses Use-After-Free conditions, and demonstrates characteristics consistent with ATT&CK technique T1068, involving local privilege escalation through kernel vulnerabilities. The structural similarity to commit 4db2af929279 ("HID: appletb-kbd: fix UAF in inactivity-timer cleanup path") indicates this represents a class of issues affecting HID timer management across different Apple input device drivers in the Linux kernel ecosystem, suggesting that similar patterns may exist in other driver implementations requiring security review. The bug has remained present since the driver's introduction, highlighting the importance of thorough race condition analysis during kernel driver development and the need for comprehensive testing of device removal scenarios.