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CVE-2026-89736
usb: gadget: u_audio: Fix use-after-free on sound card disconnect
Published 2026-09-11 (37 days ago) by the Linux kernel CNA. Subsystem drivers/usb. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-89736 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | fixedDLA-4841-1 · 2026-10-17 · text | 6.1.190-1 | Update the kernel and reboot. DLA-4841-1 shipped the fix on 2026-10-17, in 6.1.190-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
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.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
drivers/usb/gadget/function/u_audio.c
- What this is
- USB SUBSYSTEMMAINTAINERS section matched on drivers/usb/ · linux-usb@vger.kernel.org · Supported
- Kernel module
- u_audio
Check it on the machine
grep -wE 'CONFIG_OF|CONFIG_PCI|CONFIG_USB|CONFIG_USB_GADGET|CONFIG_USB_PHY|CONFIG_USB_SUPPORT|CONFIG_USB_U_AUDIO' /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w u_audioPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookwormMnot built on amd64/amd64, amd64/cloud-amd64, amd64/rt/amd64, arm64/cloud-arm64, i386/686, i386/686-pae, i386/rt/686-pae, ppc64el/powerpc64le
- trixieMnot built on amd64/amd64, amd64/cloud-amd64, amd64/rt/amd64, arm64/cloud-arm64, armel/rpi, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, s390x/s390x
- forky, sidMnot built on amd64/amd64, amd64/cloud-amd64, amd64/rt-amd64, arm64/cloud-arm64, loong64/loong64, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, s390x/s390x
- bookworm · linux-6.12Mnot built on amd64/amd64, amd64/cloud-amd64, amd64/rt/amd64, arm64/cloud-arm64, ppc64el/powerpc64le, ppc64el/powerpc64le-64k
- M
- a module where it is built at all; some flavours do not build it
- Build switches
- CONFIG_OF, CONFIG_PCI, CONFIG_USB, CONFIG_USB_GADGET, CONFIG_USB_PHY, CONFIG_USB_SUPPORT, CONFIG_USB_U_AUDIO
- Reads as
- all on means the file is compiled; any one off means it is not.
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-09-11 (37 days ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.13%, higher than 2.1% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- drivers/usb
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.10.177 | 5.10.270 | a7ecd1a04f4f |
| 5.15.105 | 5.15.221 | f983793f0314 |
| 6.1.22 | 6.1.188 | 6f46762196f0 |
| 6.3 | 6.6.157 | 891a8d11f4d5 |
| 6.3 | 6.12.109 | c74ff0b1a0fc |
| 6.3 | 6.18.50 | 4e747c864a88 |
| 6.3 | 7.2.4 | 79a92896e2bb |
| 6.3 | 7.3 | 858965947081 |
| 4.14.312 | 0 | 0 |
| 4.19.280 | 0 | 0 |
| 5.4.240 | 0 | 0 |
| 6.2.9 | 0 | 0 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4841-1 | 2026-10-17 | bookworm 6.1.190-1 | tracker |
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- The UAF is reached from local userspace: configfs UDC unbind calls afunc_unbind/f_audio_unbind → g_audio_cleanup, which frees snd_uac_chip while ALSA kctl/PCM fds still reference it; g_audio_setup runs at function bind with no USB host required, matching gadget teardown scores such as CVE-2024-38628.
- AC:LAttack complexity, low
- The attacker controls both sides by issuing SNDRV_CTL_IOCTL_ELEM_READ/WRITE on the UAC mixer kctls while concurrently unbinding the gadget; snd_card_disconnect does not drain in-flight ioctls before g_audio_cleanup kfree()s the chip, so kctl get/put callbacks dereference freed uac_rtd_params and the race is freely retryable.
- PR:LPrivileges required, low
- Android and embedded USB gadget HALs commonly delegate /sys/kernel/config/usb_gadget UDC writes to non-root service accounts, and the UAC gadget's ALSA control/PCM nodes are reachable by unprivileged local users; init-namespace root is not required once the gadget is deployed.
- UI:NUser interaction, none
- The attacker performs gadget unbind, holds ALSA fds, and issues mixer ioctls itself; no separate victim action such as plugging a cable or mounting a filesystem is required.
- S:UScope, unchanged
- The use-after-free corrupts kernel heap objects (snd_uac_chip and its playback/capture rings) within the same host kernel security authority; no VM, IOMMU, or sandbox boundary is crossed.
- C:HConfidentiality impact, high
- Kctl get/info/tlv callbacks (u_audio_volume_get, u_audio_rate_get, u_audio_volume_tlv) read volume, rate, and TLV fields from the already-freed snd_uac_chip and copy them to userspace, yielding a use-after-free disclosure primitive that kernel scoring treats as High confidentiality.
- I:HIntegrity impact, high
- Kctl put callbacks (u_audio_volume_put, u_audio_mute_put, u_audio_pitch_put) take prm->lock and write volume/mute/pitch into the kfree()'d snd_uac_chip, providing a write-after-free primitive that can be turned into arbitrary write or control-flow hijack.
- A:HAvailability impact, high
- Use of the freed snd_uac_chip, including spin_lock_irqsave on prm->lock and USB ISO completions with req->context pointing into the freed object, reliably produces KASAN reports, oops, and kernel panic.