Cloudanix VulnDB

CVE-2026-89736

High · 7.8

CVSS

7.8

EPSS

0.1%

Published

Sep 11, 2026

CISA due date

—

Cloudanix analysis

Next patch cycle SSVC: Track

A flaw in Linux USB audio gadget handling can let a local user crash the system or gain elevated access by closing sound controls after a disconnect.

Exploitation
Local Privilege
Attacker needs
Low Privilege
Complexity
Low
Impact
Full Compromise
Component
OS kernel
Class
Use After Free
Remediation
Upgrade
Effort
Medium
Patch risk
Low

What it actually does

Use-after-free in Linux kernel USB gadget audio driver where snd_card_free_when_closed returns asynchronously after immediate freeing of snd_uac_chip, allowing kctl callbacks to dereference freed private_data pointers to c_prm/p_prm structures.

Why it matters to the business

Local attackers on affected Linux systems can trigger memory corruption leading to crashes, privilege escalation, or denial of service, with elevated risk on devices exposing USB audio gadget interfaces.

How an attack unfolds

A local attacker with access to trigger USB gadget disconnect while userspace ALSA control applications hold open file descriptors causes the freed uac structure to be accessed via stale kctl private_data pointers, resulting in UAF memory corruption.

How to fix it

Apply the upstream kernel fix that registers a card->private_free callback (u_audio_card_free) during g_audio_setup to defer snd_uac_chip destruction until the sound card reference count reaches zero.

How to confirm the fix worked

Verify kernel source contains the u_audio_card_free callback registration and that g_audio_cleanup no longer calls snd_card_free_when_closed before freeing the uac context; test by opening controls, disconnecting, and confirming no UAF on close.

Typical attack path

  1. Obtain local access on target Linux system using USB gadget audio
  2. Open ALSA control file descriptors via userspace application
  3. Trigger sound card disconnect via gadget teardown
  4. Access or close open descriptors to invoke kctl callbacks on freed memory
  5. Exploit resulting UAF for memory corruption or code execution

How to detect it

Inspect kernel logs for UAF oops or slab corruption involving snd_uac_chip or u_audio structures; correlate with USB gadget disconnect events followed by ALSA control activity.

  • u_audio_card_free
  • snd_uac_chip
  • g_audio_cleanup
  • kctl->private_data
  • uac->c_prm
  • uac->p_prm

What your security team should do

  • Prioritize kernel updates on all systems exposing USB gadget audio functionality
  • Restrict local user access to USB gadget interfaces where possible
  • Monitor for kernel oops or UAF-related crashes in audio gadget code paths
  • Audit custom gadget drivers for similar async teardown patterns

The record

In the Linux kernel, the following vulnerability has been resolved: usb: gadget: u_audio: Fix use-after-free on sound card disconnect g_audio_cleanup() invokes snd_card_free_when_closed() to initiate sound card teardown and immediately frees the underlying struct snd_uac_chip context. However, snd_card_free_when_closed() returns asynchronously while ALSA control elements (kctls) remain open in userspace. When userspace control applications access or close these open file descriptors, kctl callbacks attempt to dereference kctl->private_data pointing to &uac->c_prm or &uac->p_prm within the freed uac structure, resulting in a use-after-free (UAF) memory corruption. Fix this issue by deferring the destruction of struct snd_uac_chip until all references to the ALSA sound card are released. Register a custom card->private_free callback (u_audio_card_free) during g_audio_setup() that frees uac and its associated playback/capture request and ring buffers only when the sound card reference count drops to zero.

Affected packages

Ecosystem Package Introduced Fixed