CVE-2026-80968: Linux Kernel ALSA Privilege Escalation Flaw

CVE-2026-80968 is a privilege escalation vulnerability in the Linux kernel ALSA mts64 driver caused by improper card index validation. This flaw could allow OOB access leading to elevated privileges. This article covers technical details, affected versions, impact assessment, and mitigation strategies.

CVE-2026-80968 Overview

CVE-2026-80968 is a Linux kernel vulnerability in the Advanced Linux Sound Architecture (ALSA) mts64 driver. The driver validates the devptr->id value at probe time but fails to check for negative identifier values. When the driver is bound through sysfs, callers may supply values such as "none" that resolve to negative integers. This missing check can lead to out-of-bounds access on the index[] array and other driver parameters. The fix adds a sanity check for the card index and warns or corrects the value when it falls outside the valid range.

Critical Impact
A local user with permission to bind kernel drivers via sysfs can trigger out-of-bounds memory access in the ALSA mts64 driver, resulting in kernel memory corruption or denial of service.

Affected Products

Linux kernel — ALSA mts64 sound driver
Multiple stable kernel branches referenced by the upstream fix commits
Systems exposing the mts64 driver through sysfs binding

Discovery Timeline

2026-09-11 - CVE-2026-80968 published to the National Vulnerability Database
2026-09-14 - Last updated in NVD database

Technical Details for CVE-2026-80968

Vulnerability Analysis

The ALSA mts64 driver supports the Miditerminal 4140 MIDI interface on the Linux kernel. During probe, the driver reads devptr->id to determine the card index used for indexing arrays such as index[] and related per-card parameter tables. The existing validation checks the upper bound of devptr->id but does not reject negative values. When a user binds the device through sysfs with an identifier like "none", the resulting integer can be negative and bypass the existing range check. The driver then uses the negative index to dereference array entries, producing an out-of-bounds read or write in kernel memory. The upstream fix introduces a sanity check that warns on invalid indices and corrects the value to a safe range before it is used.

Root Cause

The root cause is incomplete input validation on the card index parameter supplied during driver probe. The original bounds check only compared against the maximum permitted index and treated the value as effectively unsigned. Negative identifiers passed by the sysfs bind path were never rejected, allowing arbitrary negative offsets into fixed-size driver arrays.

Attack Vector

Exploitation requires local access with privileges sufficient to write to sysfs bind attributes for the mts64 driver, typically root or a user with the CAP_SYS_ADMIN capability. An attacker binds the driver using an identifier that resolves to a negative card index. The driver probe path then performs out-of-bounds access using that index, which can cause kernel memory corruption, unpredictable driver state, or a system crash.

No verified public exploit code is available. Refer to the upstream fix commits linked under references for the exact code change:

Detection Methods for CVE-2026-80968

Indicators of Compromise

Kernel log entries from the ALSA mts64 driver referencing invalid card indices or newly added sanity-check warnings
Kernel oops or panic traces originating in snd_mts64 probe functions
Unexpected writes to /sys/bus/*/drivers/snd-mts64/bind from non-administrative processes

Detection Strategies

Monitor dmesg and journalctl -k for warnings emitted by the patched mts64 sanity check or for oops traces referencing sound driver symbols
Audit sysfs bind and unbind operations on ALSA drivers using auditd rules on /sys/bus/platform/drivers/ and related paths
Inventory kernel versions across Linux endpoints and flag hosts that lack the fix commits listed in the vendor references

Monitoring Recommendations

Forward kernel logs to a centralized log platform and alert on ALSA driver crashes or repeated bind attempts
Track privileged process activity that interacts with sysfs driver binding interfaces
Correlate sound driver probe failures with local user or container activity to identify potential abuse attempts

How to Mitigate CVE-2026-80968

Immediate Actions Required

Apply the stable kernel updates that include the referenced fix commits from kernel.org
Restrict access to sysfs driver bind and unbind interfaces to trusted administrators only
Blacklist the snd-mts64 module on systems that do not require Miditerminal 4140 MIDI hardware support

Patch Information

The fix adds a sanity check for the card index in the mts64 probe path. It warns when the value is out of range and corrects it before it is used to index driver arrays. Backports are available across multiple stable branches through the following commits: 036e7aa, 1566ca9, 5168a62, 5d986d8, 9cd7c59, a4e774e, cf3af45, and d18a260. See the Linux Kernel Commit 5d986d8 and Linux Kernel Commit cf3af45 references for backport details.

Workarounds

Prevent the snd-mts64 module from loading by adding blacklist snd-mts64 to /etc/modprobe.d/
Remove or restrict permissions on sysfs driver bind entries so unprivileged workloads cannot trigger driver probes
On systems that do not expose MIDI hardware, unload the module with modprobe -r snd-mts64 until the kernel is patched

bash

# Configuration example: prevent the vulnerable driver from loading
echo "blacklist snd-mts64" | sudo tee /etc/modprobe.d/disable-mts64.conf
sudo modprobe -r snd-mts64 2>/dev/null || true
sudo update-initramfs -u