---
id: "CVE-2026-98742"
kind: "vulnerability"
aliases: ["CVE-2026-98742"]
title: "Linux ALSA sequencer: racing compat port ioctls can free a subscriber twice"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["alsa", "kernel", "linux", "multi-user-hosts", "runtime"]
not_affected_if: ["snd-seq-not-loaded"]
published_at: "2026-10-18T16:17:27+00:00"
first_seen_at: "2026-10-23T21:57:16+00:00"
updated_at: "2026-10-25T05:17:03+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98742", "first_seen_at": "2026-10-23T21:57:16+00:00"}]
---

# Linux ALSA sequencer: racing compat port ioctls can free a subscriber twice

Concurrent 32-bit compatibility port-info ioctl calls to the ALSA sequencer skip the client mutex, so port indexes can wrap onto existing ones. Later subscriber teardown then reaches a freed subscriber, which can corrupt kernel memory.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- `uname -r` to see the running kernel version, then compare it against the fixed kernel in the NVD entry
- Check whether the ALSA sequencer is loaded with `lsmod | grep snd_seq`; if it is absent, the flaw is not reachable
- unknown

## Fix

- Update the Linux kernel to a release that includes the upstream commit 'ALSA: seq: Serialize compat port-info ioctls'
- unknown

## Timeline

- 2026-10-23T21:57:16+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98742

## From the sources

In the Linux kernel, the following vulnerability has been resolved:

ALSA: seq: Serialize compat port-info ioctls

The native sequencer ioctl path serializes handler calls with
client->ioctl_mutex, but the translated port-info compat path invokes the
same handlers through snd_seq_kernel_client_ctl() without taking that
mutex.

This lets concurrent compat CREATE_PORT requests pass the port-count
check before any request reaches the serialized insertion. The computed
integer port index can then exceed the address field range and wrap to an
existing index. Subsequent subscriber teardown can resolve the duplicate
address to the wrong port and access a freed subscriber.

Take ioctl_mutex while dispatching converted port-info requests, matching
the native ioctl path. All translated port-info commands share this
helper, so their accesses to the client port state are serialized as
well.

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