CVE-2026-97929 in Linux
Summary
by MITRE • 09/25/2026
In the Linux kernel, the following vulnerability has been resolved:
ALSA: usbusx2y: validate URB actual_length in interrupt callback
i_usx2y_in04_int() processes the interrupt URB data without checking urb->actual_length. A short transfer from a malfunctioning device would cause the handler to process uninitialized heap data from the kmalloc-allocated in04_buf, which is then copied to the mmap-accessible ctl_snapshot[] array.
Fix by using kzalloc() for in04_buf to zero-initialize the buffer, and adding an actual_length check to skip processing on short transfers while still resubmitting the URB.
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Analysis
by VulDB Data Team • 09/25/2026
The Linux kernel's Advanced Linux Sound Architecture (ALSA) subsystem contains a critical memory safety vulnerability within the usbusx2y USB audio driver interface. This specific flaw resides in the interrupt callback function i_usx2y_in04_int, which is responsible for processing incoming data from connected USB devices. The core technical deficiency involves the handler's failure to validate the actual_length field of the Uniform Resource Block (URB) structure before proceeding with data processing operations. In standard USB driver development, the actual_length field indicates how many bytes were successfully transferred by the device during a specific transaction. When this value is not checked against expected buffer sizes or zero values, the driver assumes that valid data has been received and proceeds to manipulate memory buffers based on potentially incorrect assumptions about data availability.
The operational impact of this oversight becomes severe when interacting with malfunctioning or malicious USB devices that return short transfers or empty responses. In such scenarios, the handler accesses in04_buf, a buffer allocated via kmalloc for storing incoming interrupt data. Because kmalloc does not guarantee zero-initialization of memory contents, any bytes beyond the actual transferred length remain as uninitialized heap data from previous allocations. By failing to verify that actual_length is sufficient or non-zero before copying this data into ctl_snapshot[], an array accessible through mmap mappings, the driver inadvertently exposes these uninitialized kernel heap regions to user-space applications. This creates a classic information disclosure vulnerability where sensitive kernel memory contents can be read by local users who have access to the associated audio device interface.
From a security architecture perspective, this flaw aligns with CWE-908, which describes the use of uninitialized resource in software systems that leads to unpredictable behavior or data leakage. Furthermore, it relates closely to CWE-125, Out-of-bounds Read, as the processing logic may attempt to interpret memory regions outside the valid bounds of received data if length checks are omitted entirely. In terms of adversarial tactics, this vulnerability facilitates privilege escalation and information gathering phases within the MITRE ATT&CK framework by allowing an attacker with local access to leak kernel pointers or other sensitive state information that could be leveraged for further exploitation steps such as bypassing Kernel Address Space Layout Randomization (KASLR).
The resolution implemented in the patch addresses both the immediate symptom and the underlying memory management weakness. First, the allocation method for in04_buf was changed from kmalloc to kzalloc. This ensures that every time the buffer is allocated, it is explicitly zero-initialized by the kernel allocator, thereby neutralizing the risk of leaking stale heap data even if a short transfer occurs. Second, and more critically, explicit validation logic was added to check urb->actual_length within the interrupt callback. If the actual length indicates no valid data or insufficient data for processing, the handler now skips the copy operation entirely while still resubmitting the URB to maintain proper device communication flow. This defensive programming approach ensures that only verified, complete, and safe data is ever exposed through the mmap interface, effectively closing the information disclosure vector without disrupting normal audio functionality.