CVE-2026-52964: Linux Kernel Buffer Overflow Vulnerability

CVE-2026-52964 Overview

CVE-2026-52964 is an out-of-bounds read vulnerability in the Linux kernel's Advanced Linux Sound Architecture (ALSA) USB-audio driver. The flaw resides in the USB MIDI 2.0 endpoint descriptor parser, which reuses the same descriptor walking pattern as the legacy MIDI parser. The parser validates bLength against bNumGrpTrmBlock before reading baAssoGrpTrmBlkID[], but does not validate against the remaining bytes in the endpoint-extra scan. A malformed USB device can supply a crafted descriptor that causes subsequent baAssoGrpTrmBlkID[] reads to consume bytes past the walked descriptor boundary.

Critical Impact
A malicious or malformed USB MIDI 2.0 device can trigger out-of-bounds memory reads in the kernel by presenting crafted endpoint descriptors, enabling potential information disclosure or kernel instability.

Affected Products

Linux kernel versions containing the USB MIDI 2.0 endpoint parser in sound/usb/
ALSA USB-audio driver (snd-usb-audio)
Systems with USB host controllers exposed to untrusted MIDI devices

Discovery Timeline

2026-06-24 - CVE-2026-52964 published to the National Vulnerability Database (NVD)
2026-06-24 - Last updated in NVD database

Technical Details for CVE-2026-52964

Vulnerability Analysis

The vulnerability affects the USB MIDI 2.0 endpoint descriptor parsing path within the ALSA USB-audio driver. When the kernel walks USB endpoint-extra descriptors during device enumeration, it parses Group Terminal Block descriptors that contain a variable-length array of association IDs (baAssoGrpTrmBlkID[]). The parser performs a single bounds check that compares the descriptor's bLength field against bNumGrpTrmBlock, but it does not cross-check that the remaining bytes in the endpoint-extra buffer are sufficient to hold the declared array.

When an attacker-supplied descriptor declares a small bLength but a larger logical structure, the subsequent reads from baAssoGrpTrmBlkID[] step beyond the validated boundary. This results in reading adjacent kernel memory contents as MIDI block identifiers, leading to undefined parser behavior and possible information disclosure of adjacent descriptor or heap data.

Root Cause

The root cause is incomplete bounds validation during descriptor walking. The parser trusts the device-supplied bLength field without verifying that it is non-zero, not overlong relative to the remaining buffer, and large enough to cover the trailing variable-length array. The upstream fix rejects zero-length and overlong descriptors while walking endpoint extras, terminating the scan before any out-of-bounds access can occur.

Attack Vector

Exploitation requires physical or logical access to a USB port on the target system. An attacker connects a USB device that advertises itself as a MIDI 2.0 endpoint and returns malformed Class-Specific MIDI Streaming descriptors during enumeration. The host kernel parses the descriptors automatically when the device is bound by the snd-usb-audio driver, triggering the out-of-bounds read without any user interaction beyond plugging in the device.

No synthetic exploitation code is provided. The vulnerable code path and corrective patches are available in the upstream commits referenced in the Linux Kernel Commit history.

Detection Methods for CVE-2026-52964

Indicators of Compromise

Unexpected USB device enumeration events in dmesg or journalctl referencing snd-usb-audio with malformed descriptor warnings
Kernel KASAN reports flagging out-of-bounds reads inside ALSA USB MIDI parsing functions
USB devices presenting MIDI 2.0 class descriptors with inconsistent bLength values relative to declared block counts

Detection Strategies

Enable Kernel Address Sanitizer (KASAN) on test systems to catch out-of-bounds reads in the ALSA USB MIDI parser during device enumeration
Audit USB device connection telemetry for unknown MIDI 2.0 class devices, especially on servers and workstations not expected to handle audio peripherals
Compare running kernel versions against the fixed commits referenced in the advisory to identify unpatched hosts

Monitoring Recommendations

Forward kernel logs containing usb, snd-usb-audio, and MIDI substrings to a centralized log platform for correlation
Alert on new USB vendor and product ID combinations enumerating MIDI class interfaces in production environments
Track USB device plug events on critical hosts and flag anomalies in descriptor parsing or driver binding failures

How to Mitigate CVE-2026-52964

Immediate Actions Required

Apply the upstream Linux kernel patches referenced in the advisory and rebuild or upgrade affected kernels
Restrict physical access to USB ports on servers, kiosks, and shared workstations
Disable the snd-usb-audio kernel module on systems that do not require USB audio or MIDI functionality

Patch Information

The fix rejects zero-length and overlong descriptors while walking USB MIDI 2.0 endpoint extras, preventing reads past the validated descriptor boundary. The corrective patches are available in the following upstream commits:

Workarounds

Blacklist the snd-usb-audio module on systems that do not need USB audio support using /etc/modprobe.d/
Enforce USB device allowlisting via udev rules or USBGuard to block unauthorized MIDI 2.0 devices
Apply physical port locks or disable unused USB controllers in BIOS or UEFI on high-value hosts

bash

# Configuration example: blacklist the ALSA USB audio module
echo "blacklist snd-usb-audio" | sudo tee /etc/modprobe.d/blacklist-snd-usb-audio.conf
sudo update-initramfs -u
sudo modprobe -r snd-usb-audio