CVE-2026-98428 in Linux
Summary
by MITRE • 10/14/2026
In the Linux kernel, the following vulnerability has been resolved:
ALSA: usb: 6fire: Avoid embedded URBs
The USB 6fire driver uses URBs embedded in different structs for PCM, MIDI and communication, and this is basically a buggy implementation nowadays; since a URB is managed with a refcount, this may lead to a UAF when the URB is released asynchronously.
For addressing the problem, this patch converts those embedded URBs to ones that are properly allocated via usb_alloc_urb(). The pcm_urb.packets[] is gone, as it's allocated by usb_alloc_urb(), hence
it's found in urb.iso_frame_desc[] instead.
The conversions are rather straightforward; each embedded struct urb is changed to a pointer, and its callers are updated accordingly. The resource for those structs are released in the common destructor functions (usb6fire_comm_free(), etc), which are called at both the init error path and the disconnect.
No functional changes, only compile-tested.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 10/14/2026
The Linux kernel's Advanced Linux Sound Architecture subsystem contains a driver for the M-Audio 6Fire USB audio interface that suffers from improper memory management of Universal Request Blocks. In this specific implementation, URBs were embedded directly within various data structures used for PCM audio streams, MIDI communication, and general device control. This design choice creates a critical flaw because URB objects in the Linux kernel are reference-counted entities managed by the USB core subsystem to handle asynchronous operations safely. When an URB is allocated statically or embedded within another structure rather than being dynamically allocated with usb_alloc_urb(), it does not adhere to the expected lifecycle management protocols. Specifically, when such an embedded URB is released asynchronously after a disconnect event or during error handling paths, the reference counting mechanism may attempt to free memory that was never heap-allocated in a manner compatible with kfree, leading to undefined behavior and potential use-after-free conditions.
This vulnerability represents a classic instance of improper resource management where the allocation strategy conflicts with the deallocation logic enforced by the kernel's USB subsystem. The core issue lies in the mismatch between how the URB is created and how it is destroyed. Because the embedded structures are part of larger structs that may persist or be accessed after certain asynchronous callbacks trigger, any attempt to release the URB can result in accessing freed memory if the reference count logic assumes a standard dynamic allocation model. This scenario aligns with CWE-416, Use After Free, as well as CWE-755, Improper Handling of Exceptional Conditions, since the error paths and disconnect handlers fail to correctly manage the lifetime of these embedded resources. The risk is exacerbated by the asynchronous nature of USB I/O operations, where timing issues can expose race conditions or stale pointer dereferences if the underlying memory state becomes inconsistent during teardown sequences.
The operational impact of this vulnerability includes potential kernel crashes, data corruption, and in worst-case scenarios, privilege escalation if an attacker can trigger the specific code paths that lead to the asynchronous release of these URBs. By converting the embedded URBs into dynamically allocated pointers using usb_alloc_urb(), the patch ensures that each URB has a proper reference count and memory footprint managed by the kernel's standard allocation mechanisms. This change also necessitates updating all callers to handle pointer indirection rather than direct struct access, particularly for fields like pcm_urb.packets which are now accessed via urb.iso_frame_desc after dynamic allocation. The resource cleanup is centralized in common destructor functions such as usb6fire_comm_free, ensuring that memory is correctly released during both initialization failure paths and device disconnect events, thereby eliminating the ambiguity of when embedded structures should be freed relative to their containing structs.
From a mitigation perspective, this issue has been resolved through upstream kernel patching which enforces strict adherence to USB subsystem allocation standards. System administrators managing systems with M-Audio 6Fire devices must ensure that the Linux kernel is updated to include this fix. For organizations unable to immediately update kernels, disabling the specific ALSA usb audio driver for the 6fire device via modprobe blacklist configurations can serve as a temporary workaround to prevent exploitation vectors related to USB enumeration and disconnection events. Long-term remediation involves continuous monitoring of kernel updates and adherence to secure coding practices that prioritize dynamic allocation for objects managed by reference-counted subsystems, thereby preventing similar structural mismatches in future driver developments. This case underscores the importance of aligning hardware-specific drivers with core subsystem expectations regarding memory lifecycle management to maintain system stability and security integrity.