CVE-2026-98266 in Linux
Summary
by MITRE • 10/06/2026
In the Linux kernel, the following vulnerability has been resolved:
ALSA: core: Fix potential UAF after asynchronous card release
Usually a sound driver releases the resources assigned to the card via snd_card_free(), and it synchronizes with the whole release procedure. However, when the card is released asynchronously via snd_card_free_when_closed() like USB-audio driver, the situation is slightly different; although the snd_card_disconnect() call at the disconnection guarantees that any newer accesses will be gated, the in-flight tasks might be still accessing to the underlying card->dev device even after the disconnection, which would cause a use-after-free in the end, as reported by fuzzers.
For addressing the bug above, this patch takes the refcount of card->dev at initialization of the card object, and releases at its destructor. This assures the availability of the card->dev in its whole lifecycle.
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Analysis
by VulDB Data Team • 10/07/2026
The Linux kernel's Advanced Linux Sound Architecture (ALSA) subsystem contains a critical use-after-free vulnerability that arises during the asynchronous release of sound cards, particularly affecting USB-audio drivers. In standard operation, sound drivers manage resource allocation and deallocation through synchronous calls such as snd_card_free(), which ensures that all associated resources are properly released only after confirming that no active processes are accessing them. This synchronization prevents race conditions where a driver might attempt to access memory or hardware devices that have already been freed by the kernel's cleanup routines. However, when a sound card is disconnected from the system bus, such as in the case of unplugging a USB audio device, the release process often shifts to an asynchronous model via snd_card_free_when_closed(). This function defers the actual freeing of resources until all open file descriptors associated with the card are closed, aiming to prevent immediate disruption to ongoing playback or recording sessions.
The core technical flaw lies in the handling of the underlying device structure, specifically card->dev, during this deferred release phase. While snd_card_disconnect() effectively gates new access attempts by marking the connection as inactive, it does not stop tasks that were already executing at the moment of disconnection. These in-flight kernel threads or interrupt handlers may continue to reference and manipulate the card->dev object even after the disconnect signal has been issued. Because the asynchronous release mechanism delays the actual deallocation until all users have closed their handles, there exists a window where these lingering tasks can access memory that is scheduled for deletion but not yet freed, leading to undefined behavior or crashes if the timing aligns unfavorably with other kernel operations. Fuzzing tools have successfully identified this scenario as a potential use-after-free condition, highlighting the risk of data corruption and system instability when such race conditions are exploited.
This vulnerability maps directly to CWE-416, Use After Free, where software continues to use a pointer after it has been freed, leading to unpredictable behavior that can be leveraged for denial-of-service or potentially arbitrary code execution depending on memory layout exploitation techniques. From an offensive security perspective, this aligns with ATT&CK technique T1203, Exploitation for Defense Evasion, as attackers might exploit the race condition between disconnection and final resource release to crash the kernel or escalate privileges by manipulating the state of freed objects before they are completely reclaimed by the memory allocator. The lack of proper reference counting on the device structure during this critical window allows an attacker with local access to trigger a denial-of-service attack simply by rapidly connecting and disconnecting USB audio devices, causing kernel panics that disrupt system availability.
The remediation for this issue involves implementing strict reference counting mechanisms for the card->dev object throughout its lifecycle. By incrementing the reference count during the initialization of the card object and ensuring it is only decremented in the destructor, the patch guarantees that the device structure remains valid as long as any part of the kernel holds a reference to it. This approach decouples the logical state of the sound card from the physical presence or immediate availability of the hardware interface, preventing premature deallocation while asynchronous tasks are still active. The fix ensures that snd_card_free_when_closed() waits not just for file descriptor closure but also for all internal references held by kernel threads and drivers to be released before freeing the underlying device memory.
To mitigate this vulnerability in environments where immediate patching is not feasible, administrators should consider disabling automatic suspend or power management features for USB audio devices if they are not strictly required, thereby reducing the frequency of disconnect events that trigger the asynchronous release path. Additionally, restricting physical access to USB ports can prevent unauthorized users from triggering rapid connect-disconnect cycles designed to exploit this race condition. For developers and system integrators, ensuring that all custom sound drivers adhere to synchronous release patterns where possible or properly implement reference counting for device structures is essential to maintaining kernel stability. Regular updates of the Linux kernel are critical as they incorporate these fixes into stable releases, closing the gap between hardware state changes and software resource management.