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CVE-2026-68201
ALSA: timer: drain a slave's callback before its master detaches it
Published 2026-08-10 (2 months ago) by the Linux kernel CNA. Subsystem sound/core. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-68201 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 | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | fixed | 6.12.101-1 | Update the kernel and reboot. Fixed in 6.12.101-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.6-1 | Update the kernel and reboot. Fixed in 7.1.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.6-1 | Update the kernel and reboot. Fixed in 7.1.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4745-1 · 2026-08-18 · text | 6.12.101-1~deb12u1 | Update the kernel and reboot. DLA-4745-1 shipped the fix on 2026-08-18, in 6.12.101-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
snd_timer_close_locked() drains the closing instance's own in-flight callback (IFLG_CALLBACK) before freeing it, but not its slaves'. When a master instance is closed, remove_slave_links() clears each slave's ->timer; the slave's own close then reads timer == NULL and takes the branch that skips the drain entirely (snd_timer_stop_slave() also no-ops on a NULL timer). So a slave whose callback is still running when the master is closed is freed underneath the live callback, leading to use-after-free. Drain the slaves too before remove_slave_links() severs them. snd_timer_stop() has already taken this instance off the active list, so no new slave callback can be queued. Take the slaves off the ack list so a pending one can't fire either, then wait for any that is already in flight.
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.
sound/core/timer.c
- What this is
- SOUNDMAINTAINERS section matched on sound/ · linux-sound@vger.kernel.org · Maintained
- Kernel module
- snd_timer
Check it on the machine
grep -wE 'CONFIG_SND|CONFIG_SND_TIMER' /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 snd_timerPrints 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.
- bookworm, trixie, forky, sid, bookworm · linux-6.12Mnot built on amd64/cloud-amd64, arm64/cloud-arm64
- M
- a module where it is built at all; some flavours do not build it
- Build switches
- CONFIG_SND, CONFIG_SND_TIMER
- 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
- 2026-08-10 (2 months 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
- 0.17%, higher than 6.0% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- sound/core
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.12 | 6.12.101 | cd461bcfcdf8 |
| 6.12 | 6.18.42 | 426c0ff1c433 |
| 6.12 | 7.1.6 | 2b2989977868 |
| 6.12 | 7.2 | bdefe1346a8e |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4745-1 | 2026-08-18 | bookworm 6.12.101-1~deb12u1 | 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 bug is reached only through the local ALSA timer character device /dev/snd/timer (open, SNDRV_TIMER_IOCTL_SELECT/START/CREATE/TRIGGER, close) — no remote or network path exists into sound/core/timer.c.
- AC:LAttack complexity, low
- The attacker owns both sides of the race: it creates the master/slave instances, drives callback delivery itself via the userspace-driven timer's SNDRV_TIMER_IOCTL_TRIGGER ioctl, and chooses the close ordering, and can widen the window with many slaves and queued events, so the UAF is reliably reproducible.
- PR:LPrivileges required, low
- No capable() or CAP_* check exists on any part of the path; any local user with access to /dev/snd/timer (normal for desktop/Android audio-group users and sandboxed apps) can create utimers and open master and slave instances.
- UI:NUser interaction, none
- A single unprivileged process performs all steps — open, select, start, trigger and close — with no action from any other user or victim process required.
- S:UScope, unchanged
- The corruption is confined to the kernel's own heap and the ALSA timer subsystem; no VM, IOMMU or other security-authority boundary is crossed.
- C:HConfidentiality impact, high
- The freed snd_timer_instance/snd_timer_user objects can be reclaimed by attacker-sprayed data, and the still-running callback reads and later exposes freed-slab contents through the timer read queue, enabling disclosure of arbitrary kernel heap data.
- I:HIntegrity impact, high
- The in-flight callback writes attacker-influenced tread records into the already-freed tqueue and performs list and waitqueue updates on freed memory, giving a controllable use-after-free write usable for heap corruption and control-flow hijack.
- A:HAvailability impact, high
- The use-after-free corrupts slab memory and list pointers, readily producing an oops, list_del corruption BUG or panic that takes down the whole system.