CVE-2025-40269 in Linux
Summary
by MITRE • 12/07/2025
In the Linux kernel, the following vulnerability has been resolved:
ALSA: usb-audio: Fix potential overflow of PCM transfer buffer
The PCM stream data in USB-audio driver is transferred over USB URB packet buffers, and each packet size is determined dynamically. The packet sizes are limited by some factors such as wMaxPacketSize USB descriptor. OTOH, in the current code, the actually used packet sizes are determined only by the rate and the PPS, which may be bigger than the size limit above. This results in a buffer overflow, as reported by syzbot.
Basically when the limit is smaller than the calculated packet size, it implies that something is wrong, most likely a weird USB descriptor. So the best option would be just to return an error at the parameter setup time before doing any further operations.
This patch introduces such a sanity check, and returns -EINVAL when the packet size is greater than maxpacksize. The comparison with ep->packsize[1] alone should suffice since it's always equal or
greater than ep->packsize[0].
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Analysis
by VulDB Data Team • 02/23/2026
The vulnerability identified as CVE-2025-40269 represents a critical buffer overflow condition within the Linux kernel's ALSA USB-audio driver component. This flaw exists in the handling of PCM (Pulse Code Modulation) stream data transfer over USB Universal Resource Bus communication channels. The USB-audio driver utilizes URB (USB Request Block) packet buffers to facilitate data transfer between USB audio devices and the system's audio subsystem, where each packet size is dynamically determined based on audio sample rates and period parameters.
The technical implementation flaw stems from an inadequate validation mechanism that fails to properly enforce USB descriptor limitations during the audio stream initialization phase. Specifically, the driver calculates packet sizes based on audio rate and period parameters without adequately verifying that these calculated values remain within the constraints imposed by the USB endpoint's wMaxPacketSize descriptor. This mismatch occurs because the current code determines packet sizes using only rate and PPS (Periods Per Second) parameters while ignoring the fundamental USB protocol constraints that govern maximum packet sizes for each endpoint. The vulnerability manifests when dynamically calculated packet sizes exceed the maximum packet size limits defined in the USB descriptors, creating a scenario where buffer overflow conditions can occur during data transfer operations.
The operational impact of this vulnerability extends beyond simple data corruption, as it represents a potential attack vector that could be exploited to cause system instability or facilitate privilege escalation within the kernel space. When packet sizes exceed the USB descriptor limits, the system encounters buffer overflow conditions that can result in memory corruption, system crashes, or potentially allow malicious actors to execute arbitrary code with kernel privileges. This risk is particularly concerning given that the vulnerability affects the core ALSA USB-audio subsystem that handles audio input/output operations for numerous audio devices including microphones, speakers, and audio interfaces. The syzbot automated testing system identified this issue, indicating it likely occurs under specific audio configuration scenarios involving USB audio devices with non-standard or malformed USB descriptors.
The mitigation strategy implemented in this patch addresses the vulnerability through proactive input validation and parameter checking. The fix introduces a sanity check mechanism that verifies packet size calculations against the maximum packet size limits defined in the USB endpoint descriptors before any actual data transfer operations commence. When the calculated packet size exceeds the maximum packet size limit (specifically comparing against ep->packsize[1] which is always equal to or greater than ep->packsize[0]), the driver returns a -EINVAL error code to indicate invalid parameters. This approach aligns with security best practices by preventing potentially harmful operations from executing and follows the principle of least privilege by rejecting malformed configurations at the earliest possible stage of parameter processing. The solution directly addresses the underlying CWE-129 vulnerability pattern related to insufficient input validation and incorporates elements consistent with the ATT&CK framework's privilege escalation techniques by preventing unauthorized kernel memory access patterns. This defensive programming approach ensures that audio device configurations with malformed USB descriptors cannot proceed to cause buffer overflows, thereby maintaining system stability and preventing potential exploitation scenarios while preserving legitimate audio functionality for compliant devices.