CVE-2026-97930 in Linux
Summary
by MITRE • 09/25/2026
In the Linux kernel, the following vulnerability has been resolved:
ALSA: usbusx2y: fix in04_last array size mismatch with in04_buf
The in04_last array in struct usx2ydev is declared as char[24], but
in04_buf is allocated as sizeof(struct us428_ctls) which is 21 bytes. In i_usx2y_in04_int(), when ctl_snapshot_last == -2 (initialization path):
memcpy(usx2y->in04_last, usx2y->in04_buf, sizeof(usx2y->in04_last));
This copies 24 bytes from a 21-byte slab allocation, reading 3 bytes past the end of the source object.
Introduce a USX2Y_IN04_SIZE constant defined as sizeof(struct us428_ctls) and use it consistently for the in04_last array, the in04_buf allocation, the URB transfer length, and the comparison loop, replacing the bare 24 and 21 literals throughout.
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Analysis
by VulDB Data Team • 09/25/2026
The Linux kernel's Advanced Linux Sound Architecture (ALSA) subsystem contains a memory safety vulnerability within the usbusx2y USB audio driver that results in an out-of-bounds read operation. This flaw stems from a structural inconsistency where the destination buffer, specifically the in04_last array defined as char[24] within the struct usx2ydev structure, is larger than the source buffer allocated for it. The source buffer, known as in04_buf, is dynamically allocated based on the size of the struct us428_ctls structure, which occupies only 21 bytes. This discrepancy creates a scenario where memory operations attempt to transfer data from a smaller allocation into a larger fixed-size array without proper boundary checks relative to the actual source capacity.
The vulnerability manifests during the initialization phase of the driver's interrupt endpoint handling function, i_usx2y_in04_int(). When the control snapshot state is set to -2, indicating an initialization path, the code executes a memcpy operation that copies sizeof(usx2y->in04_last) bytes from in04_buf. Since this size evaluates to 24 bytes while the source allocation contains only 21 bytes, the function reads three bytes past the end of the allocated slab object. This constitutes an out-of-bounds read vulnerability where kernel memory beyond the intended buffer boundary is accessed. Such access patterns can potentially expose sensitive kernel data or lead to unpredictable system behavior depending on what resides in the adjacent memory regions.
From a technical classification perspective, this issue aligns with CWE-125, which describes Out-of-Bounds Read vulnerabilities. The improper limitation of array bounds allows for reading beyond allocated limits, violating fundamental principles of safe memory management. In terms of attack vector and tactical mapping under MITRE ATT&CK, this flaw relates to techniques involving unauthorized access to system information or potential exploitation through data leakage if the read values are subsequently used in logic that influences control flow. While primarily a stability issue, out-of-bounds reads can sometimes be leveraged for information disclosure or as part of more complex exploit chains targeting kernel integrity.
The operational impact of this vulnerability includes potential kernel panics due to accessing unmapped memory pages, which would result in system crashes and denial of service conditions. Even if the accessed memory is mapped, reading uninitialized or unrelated data can lead to logic errors within the audio processing pipeline, causing corrupted sound output or driver instability. For systems relying on these specific USB audio interfaces, such instabilities disrupt continuous operation and require manual intervention or reboots to restore functionality.
To mitigate this vulnerability, the resolution involves refactoring the code to enforce consistent sizing across all related structures and operations. A new constant, USX2Y_IN04_SIZE, is introduced and defined as sizeof(struct us428_ctls). This ensures that the in04_last array declaration, the dynamic allocation of in04_buf, the USB Request Block transfer length, and subsequent comparison loops all utilize a single source of truth for size determination. By replacing hardcoded literals like 24 and 21 with this consistent constant, the mismatch is eliminated at compile time or through uniform runtime behavior. This approach prevents future drift between buffer declarations and allocations, enhancing code maintainability and security posture by adhering to strict memory boundary constraints.