CVE-2026-98837 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
ALSA: caiaq: unregister the input device when probe fails
setup_card() registers the input device, whose name and phys point into struct snd_usb_caiaqdev, and then goes on to snd_card_register() and snd_usb_caiaq_control_init(). If either fails, snd_probe() calls snd_card_free(), which frees the device state but leaves the input device registered: card_free() only clears the pointer, and the input device is unregistered from snd_disconnect() alone. Reading its "uevent" attribute afterwards dereferences freed memory:
BUG: KASAN: slab-use-after-free in string+0x4a9/0x4f0 Read of size 1 at addr ffff8880208f5043 by task caiaq/4967 add_uevent_var+0x183/0x3a0 input_dev_uevent+0x162/0x900 dev_uevent+0x2f1/0x870 uevent_show+0x1ca/0x3a0 ...
Unregister the input device on the probe error path, as snd_disconnect() does. snd_usb_caiaq_input_disconnect() is a no-op when no input device was registered.
Reproduced with a raw-gadget Audio Kontrol 1 and a temporary hack that makes snd_usb_caiaq_control_init() fail.
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Analysis
by VulDB Data Team • 10/18/2026
The Linux kernel vulnerability identified in the ALSA caiaq driver represents a critical use-after-free condition arising from improper resource cleanup during device initialization failures. The core technical flaw resides within the setup_card function, which is responsible for initializing various components of the USB audio interface. During this process, an input device structure is registered with the kernel's input subsystem. Crucially, the name and physical path fields of this input device are pointers that reference memory locations within the snd_usb_caiaqdev structure. This creates a tight coupling between the lifecycle of the input device object and the underlying hardware state structure managed by the driver.
The vulnerability manifests when subsequent initialization steps fail. Specifically, if either the snd_card_register function or the snd_usb_caiaq_control_init function returns an error code, the probe routine invokes snd_card_free to release resources associated with the sound card. While this cleanup process correctly frees the memory allocated for the device state structure, it fails to unregister the previously registered input device. The snd_disconnect function, which is typically responsible for cleaning up these resources during normal disconnection or removal sequences, contains the logic to properly unreference and destroy the input device. However, because the error path in probe bypasses this disconnect routine, the kernel retains a reference to an input device whose underlying data structures have already been deallocated.
This architectural oversight leads directly to a slab-use-after-free condition as detected by Kernel Address Sanitizer (KASAN). When a user space process attempts to read the uevent attribute of the now-dangling input device node in sysfs, the kernel executes dev_uevent and subsequently string operations that attempt to access the name field. Since this pointer still points into freed memory from the snd_usb_caiaqdev structure, any read operation results in accessing invalid heap memory. The resulting crash or potential information leak demonstrates a severe integrity violation where the system attempts to dereference memory that is no longer validly mapped for use by the driver context.
From an industry standards perspective, this vulnerability aligns with CWE-416, Use After Free, which describes situations where software continues to use a pointer after it has been freed. The specific mechanism of accessing device attributes via sysfs uevent events also relates to improper resource management during error handling paths. In the context of MITRE ATT&CK for Linux, this flaw could potentially be leveraged in techniques related to System Information Discovery or Denial of Service if an attacker can trigger the probe failure condition repeatedly. The lack of proper cleanup on initialization errors is a common pattern that undermines system stability and security posture by leaving zombie objects accessible through standard interfaces.
The operational impact of this vulnerability includes kernel panics, which cause denial of service for the host system or specific services relying on stable audio input devices. Furthermore, depending on memory layout and heap state at the time of exploitation, there is a theoretical risk of information disclosure where sensitive data from previously freed allocations could be leaked through the uevent attribute read operation. This poses a significant security risk in environments where unprivileged users have access to device attributes or when automated monitoring tools frequently query such sysfs entries for hardware status updates.
To mitigate this vulnerability, the driver code must be updated to ensure that all registered resources are properly released upon any failure during the probe sequence. The recommended fix involves explicitly calling snd_usb_caiaq_input_disconnect within the error handling path of setup_card before returning an error code from snd_probe. This function is designed as a no-op if no input device was successfully registered, making it safe to call unconditionally in cleanup routines. By mirroring the logic found in snd_disconnect, developers ensure that reference counts are decremented and memory is freed correctly regardless of whether initialization succeeds or fails at any stage after registration.
System administrators should apply kernel updates containing this patch as soon as they become available through their distribution channels. For systems where immediate patching is not feasible, mitigating the risk involves restricting access to the specific sysfs attributes associated with caiaq devices if possible, although complete prevention requires addressing the root cause in the driver code itself. Regular auditing of kernel drivers for proper error path cleanup practices remains essential to prevent similar use-after-free vulnerabilities from being introduced or persisting in future releases.