CVE-2025-38249 in Linux
Summary
by MITRE • 07/09/2025
In the Linux kernel, the following vulnerability has been resolved:
ALSA: usb-audio: Fix out-of-bounds read in snd_usb_get_audioformat_uac3()
In snd_usb_get_audioformat_uac3(), the length value returned from snd_usb_ctl_msg() is used directly for memory allocation without validation. This length is controlled by the USB device.
The allocated buffer is cast to a uac3_cluster_header_descriptor and its fields are accessed without verifying that the buffer is large enough. If the device returns a smaller than expected length, this leads to an out-of-bounds read.
Add a length check to ensure the buffer is large enough for uac3_cluster_header_descriptor.
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Analysis
by VulDB Data Team • 05/02/2026
The vulnerability CVE-2025-38249 represents a critical out-of-bounds read flaw within the Linux kernel's Advanced Linux Sound Architecture implementation specifically affecting USB audio devices. This issue resides in the snd_usb_get_audioformat_uac3() function which processes audio format information from USB audio devices compliant with the USB Audio Class 3.0 specification. The flaw demonstrates a classic buffer over-read vulnerability that can be exploited through malicious USB audio hardware, making it particularly concerning for systems that support USB audio peripherals. The vulnerability is categorized under CWE-129 as an "Improper Validation of Array Index" and aligns with ATT&CK technique T1059.001 for execution through kernel-level code manipulation.
The technical implementation of this vulnerability stems from insufficient input validation within the USB audio processing pipeline. When the kernel communicates with a USB audio device, it retrieves a length value through the snd_usb_ctl_msg() function that determines how much memory to allocate for processing audio format descriptors. This length value originates from the USB device itself and is therefore completely under attacker control. The function directly uses this unvalidated length to allocate memory, subsequently casting the buffer to a uac3_cluster_header_descriptor structure and accessing its fields without first verifying that the allocated buffer contains sufficient space for the entire structure. This design flaw creates a scenario where a malicious USB device can return a length value smaller than the actual size requirements of the uac3_cluster_header_descriptor, leading to memory access beyond the allocated buffer boundaries.
The operational impact of this vulnerability extends beyond simple memory corruption, potentially enabling privilege escalation and system instability. An attacker with physical access to a target system could plug in a malicious USB audio device that returns a crafted length value, triggering the out-of-bounds read condition. This condition could result in information disclosure through memory leaks, system crashes, or potentially more severe consequences if the read operation accesses sensitive kernel memory regions. The vulnerability affects systems running Linux kernels that support USB audio class 3.0 devices, particularly those in enterprise environments where USB audio peripherals are commonly used. According to ATT&CK framework, this vulnerability could be leveraged for privilege escalation through kernel memory corruption and system compromise. The out-of-bounds read opens possibilities for information disclosure and system instability that could be exploited in various attack scenarios including supply chain attacks or physical access exploitation.
Mitigation strategies for CVE-2025-38249 focus on implementing proper input validation and bounds checking within the kernel's USB audio subsystem. The fix implemented in the kernel patch adds a length validation check before memory allocation, ensuring that the buffer allocated is sufficient to contain the uac3_cluster_header_descriptor structure. This approach aligns with security best practices and follows the principle of least privilege by preventing untrusted input from determining memory allocation sizes. System administrators should prioritize applying kernel updates containing the patched version of snd_usb_get_audioformat_uac3() function, particularly in environments where USB audio devices are frequently connected or where physical access controls are weak. Additional mitigations include implementing USB device whitelisting policies, restricting USB device access through kernel modules, and monitoring for suspicious USB device connections. Organizations should also consider implementing kernel lockdown mechanisms and ensuring that USB audio support is disabled on systems where such devices are not required, following the principle of least functionality to reduce attack surface. The vulnerability highlights the importance of validating all inputs from external devices and implementing robust bounds checking in kernel code, especially in device driver implementations that handle untrusted external data.