CVE-2026-23208: Linux Kernel Buffer Overflow Vulnerability

CVE-2026-23208 Overview

CVE-2026-23208 is an out-of-bounds write vulnerability in the Linux kernel's ALSA (Advanced Linux Sound Architecture) USB-audio subsystem. The vulnerability occurs in the copy_to_urb function within sound/usb/pcm.c when processing audio data for USB audio devices. When a user constructs PCM playback parameters with specific configurations, the calculated number of frames can exceed the allocated URB (USB Request Block) buffer size, resulting in a kernel memory corruption.

This vulnerability was discovered through syzbot, the automated kernel fuzzing system, which detected a KASAN (Kernel Address Sanitizer) slab-out-of-bounds error during write operations to the ALSA PCM playback stream.

Critical Impact

An attacker with local access could exploit this vulnerability by crafting malicious USB audio parameters to trigger an out-of-bounds write, potentially leading to denial of service, privilege escalation, or arbitrary code execution in kernel context.

Affected Products

• Linux kernel (multiple versions with ALSA USB-audio support)
• Systems with USB audio device support enabled
• Linux distributions using affected kernel versions

Discovery Timeline

• 2026-02-14 - CVE-2026-23208 published to NVD
• 2026-02-18 - Last updated in NVD database

Technical Details for CVE-2026-23208

Vulnerability Analysis

The vulnerability exists in the ALSA USB-audio PCM playback path. When processing audio data, the kernel calculates the buffer size for each data URB using the formula maxpacksize * packets. However, during write operations, the actual number of frames calculated as packsize[N] * packets can exceed this allocated buffer size.

In the reported case, the following configuration triggered the bug:

• maxpacksize: 40 bytes
• Sample rate: 22050 Hz
• Packets per second (pps): 1000
• packsize[0]: 22
• packsize[1]: 23

This results in a URB buffer size of 40 * 6 = 240 bytes, but the calculated frame count of packsize * packets yields 264 bytes worth of data to be written, exceeding the buffer boundary by 24 bytes.

Root Cause

The root cause is insufficient validation of the relationship between the calculated frame count and the allocated URB buffer size. The copy_to_urb function in sound/usb/pcm.c at line 1487 writes data without verifying that the number of frames being copied fits within the URB buffer allocation. The vulnerability stems from improper bounds checking when packsize[N] * packets exceeds maxpacksize * packets.

Attack Vector

The attack requires local access to the system with the ability to interact with USB audio devices through the ALSA subsystem. An attacker can exploit this vulnerability through the following mechanism:

1. Configure a USB audio playback stream with carefully crafted parameters
2. Set maxpacksize to a value lower than the effective packet sizes
3. Initiate a write operation to the PCM playback stream
4. The kernel copies more data than allocated, corrupting adjacent slab memory

The vulnerability was triggered through the call chain:

• copy_to_urb (sound/usb/pcm.c:1487)
• prepare_playback_urb (sound/usb/pcm.c:1611)
• prepare_outbound_urb (sound/usb/endpoint.c:333)

Detection Methods for CVE-2026-23208

Indicators of Compromise

• KASAN reports indicating slab-out-of-bounds writes in copy_to_urb function
• Kernel panic or oops messages referencing sound/usb/pcm.c
• Unexpected system crashes during USB audio playback operations
• Memory corruption artifacts detected by kernel memory debugging tools

Detection Strategies

• Enable KASAN (Kernel Address Sanitizer) to detect out-of-bounds memory access attempts
• Monitor kernel logs for ALSA USB-audio related errors or warnings using dmesg | grep -i "usb.*audio\|snd_usb"
• Deploy endpoint detection solutions capable of monitoring kernel-level memory access patterns
• Use kernel tracing tools such as ftrace to monitor the copy_to_urb and prepare_playback_urb functions

Monitoring Recommendations

• Implement centralized kernel log collection to detect exploitation attempts
• Configure alerting on KASAN or UBSAN reports related to the sound subsystem
• Monitor for unusual USB audio device enumeration patterns
• Track system stability metrics for hosts with USB audio hardware

How to Mitigate CVE-2026-23208

Immediate Actions Required

• Update the Linux kernel to a patched version that includes the frame count validation fix
• Consider disabling USB audio support if not required using kernel module blacklisting
• Restrict local user access to USB audio devices through udev rules or access controls
• Deploy SentinelOne Singularity Platform for runtime kernel-level threat detection and protection

Patch Information

The Linux kernel maintainers have released patches to address this vulnerability. The fix adds proper validation for the number of single data URB frames when calculating the total frame count, preventing the out-of-bounds write condition.

Patches are available through the following kernel git commits:

• Kernel Git Commit 282aba5
• Kernel Git Commit 480a149
• Kernel Git Commit 62932d9
• Kernel Git Commit ab0b5e9
• Kernel Git Commit c4dc012
• Kernel Git Commit d67dde0
• Kernel Git Commit e0ed5a3
• Kernel Git Commit ef5749e

Workarounds

• Blacklist the snd-usb-audio kernel module if USB audio functionality is not required
• Implement strict access controls to limit which users can access audio devices
• Use container isolation or namespacing to restrict direct USB device access
• Apply kernel hardening options such as KASAN in production to detect exploitation attempts early

# Blacklist USB audio module as a temporary workaround
echo "blacklist snd-usb-audio" | sudo tee /etc/modprobe.d/disable-usb-audio.conf
sudo update-initramfs -u

# Verify module is not loaded
lsmod | grep snd_usb_audio