CVE-2026-80812: Linux Kernel ALSA Privilege Escalation Flaw

CVE-2026-80812 Overview

CVE-2026-80812 affects the Linux kernel's Advanced Linux Sound Architecture (ALSA) dummy driver. The snd_dummy_probe() function trusts the devptr->id value without validating that it falls within the valid card index range. When the driver creates devices at module probe time, the index is safe. However, when a device is bound manually through the sysfs interface, the id can be -1 (interpreted as "none"), leading to out-of-bounds access on the index[] array and related parameters.

The fix adds a sanity check on the card index at probe and corrects it if the value falls outside the valid range.

Critical Impact
A local user with privileges to bind devices via sysfs can trigger out-of-bounds memory access in the kernel, potentially causing a denial of service or memory corruption.

Affected Products

Linux kernel with the ALSA snd-dummy driver compiled and loadable
Multiple stable kernel branches (see referenced git commits for backports)
Distributions shipping the affected sound/drivers/dummy.c code path

Discovery Timeline

2026-09-04 - CVE-2026-80812 published to NVD
2026-09-07 - Last updated in NVD database

Technical Details for CVE-2026-80812

Vulnerability Analysis

The vulnerability resides in the snd_dummy_probe() function within the ALSA dummy sound driver. The function receives a platform device pointer and uses devptr->id directly as an index into fixed-size arrays such as index[], id[], enable[], and other module parameter arrays. These arrays are sized according to the maximum supported sound cards (SNDRV_CARDS).

The driver assumes the id value is always a valid, non-negative integer within array bounds. This assumption holds for devices created programmatically during module initialization. It breaks when a user binds a device manually through the sysfs bind interface, where the platform device id can be -1 to indicate "no id assigned".

Using -1 as an array index in C produces access to memory preceding the parameter arrays. This constitutes an out-of-bounds read at minimum, and depending on downstream code paths that write based on the id, potential out-of-bounds writes.

Root Cause

The root cause is missing input validation on an externally influenced integer used as an array index. The snd_dummy_probe() function did not verify that devptr->id was within [0, SNDRV_CARDS) before using it to dereference module parameter arrays. This is an out-of-bounds access issue rooted in improper input validation.

Attack Vector

Exploitation requires local access with sufficient privileges to write to the sysfs bind interface for the snd-dummy platform driver. An attacker with such access can bind a device with id -1, triggering the probe function and forcing the out-of-bounds access. This is not remotely exploitable and requires the snd-dummy module to be loaded on the target system.

The vulnerability is described in prose because no verified proof-of-concept code is published. Refer to the upstream commits for the exact source-level fix, including Kernel Git Commit b7579e8 and the related backports.

Detection Methods for CVE-2026-80812

Indicators of Compromise

Kernel warning messages or oops entries originating from snd_dummy_probe in dmesg or /var/log/kern.log
Unexpected writes to /sys/bus/platform/drivers/snd_dummy/bind from non-root or unusual processes
Presence of the snd-dummy module loaded on systems that have no functional need for a dummy sound device

Detection Strategies

Enable KASAN (Kernel Address Sanitizer) on test kernels to surface the exact out-of-bounds access if the flaw is triggered
Audit kernel version and patch level against the fixed commits referenced in the kernel stable tree
Monitor auditd for PATH records touching sysfs bind interfaces under /sys/bus/platform/drivers/snd_dummy/

Monitoring Recommendations

Collect and centralize kernel logs to detect probe-time warnings introduced by the patched sanity check
Track loaded kernel modules across the fleet and alert on unexpected snd-dummy presence on production servers
Correlate sysfs write events with the initiating user and process to identify unauthorized bind attempts

How to Mitigate CVE-2026-80812

Immediate Actions Required

Update the Linux kernel to a version that includes the fix from the upstream commits listed in the CVE references
Blacklist the snd-dummy module on systems that do not require it by adding blacklist snd_dummy to /etc/modprobe.d/
Restrict write access to /sys/bus/platform/drivers/snd_dummy/bind and related sysfs entries to root only

Patch Information

The fix is available in the mainline and stable kernel trees. Reference commits include Kernel Git Commit 02442d5, Kernel Git Commit 3dba0e9, Kernel Git Commit 4d0892a, Kernel Git Commit 690b721, Kernel Git Commit b20eb7e, Kernel Git Commit b7579e8, Kernel Git Commit c9f10a0, and Kernel Git Commit f20c2c3. Apply the update supplied by your distribution vendor as soon as it becomes available.

Workarounds

Unload the snd-dummy module using modprobe -r snd_dummy on systems where it is not required
Add a modprobe blacklist entry to prevent automatic loading of the dummy sound driver
Ensure only privileged administrators can write to platform driver sysfs bind endpoints

bash

# Blacklist the snd-dummy module to prevent load
echo "blacklist snd_dummy" | sudo tee /etc/modprobe.d/blacklist-snd-dummy.conf
sudo modprobe -r snd_dummy 2>/dev/null || true

# Verify the module is not loaded
lsmod | grep snd_dummy