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CVE-2026-53193
ALSA: timer: Forcibly close timer instances at closing
Published 2026-06-25 (4 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-2026-53193 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 | 6.12.94-1 | Update the kernel and reboot. Fixed in 6.12.94-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.0.13-1 | Update the kernel and reboot. Fixed in 7.0.13-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.13-1 | Update the kernel and reboot. Fixed in 7.0.13-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
When snd_timer object is freed via snd_timer_free() and still pending snd_timer_instance objects are assigned to the timer object, it tries to unlink all instances and just set NULL to each ti->timer, then releases the resources immediately. The problem is, however, when there are slave timer instances that are associated with a master instance linked to this timer: namely, those slave instances still point to the freed timer object although the master instance is unlinked, which may lead to user-after-free. The bug can be easily triggered particularly when a new userspace-driven timers (CONFIG_SND_UTIMER) is involved, since it can create and delete the timer object via a simple file open/close, while the other applications may keep accessing to that timer. This patch is an attempt to paper over the problem above: now instead of just unlinking, call snd_timer_close[_locked]() forcibly for each pending timer instance, so that all assigned slave timer instances are properly detached, too. Since snd_timer_close() might be called later by the driver that created that instance, the check of SNDRV_TIMER_IFLG_DEAD is added at the beginning, too.
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, sidMnot 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
- 2026-06-25 (4 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
- 0.14%, higher than 3.1% 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 | 6.12.94 | 586b219a22b1 |
| 6.12 | 6.18.36 | f46093dd2296 |
| 6.12 | 7.0.13 | 60e73ab87b84 |
| 6.12 | 7.1 | da3039e91d1f |
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 vulnerable path is reached through local `/dev/snd/timer` opens and ALSA timer ioctls, including `SNDRV_TIMER_IOCTL_CREATE`, `SELECT`, and later access to retained timer instances.
- AC:LAttack complexity, low
- The attacker can create the userspace-driven timer, bind matching master/slave timer instances, close the timer fd to free the object, and then access the stale slave instance without relying on uncontrollable conditions.
- PR:LPrivileges required, low
- The code path has no capability checks, but it requires a local user able to open `/dev/snd/timer` and issue ioctls.
- UI:NUser interaction, none
- No victim action is required after the attacker has local access; the attacker controls all needed file descriptors and ioctls.
- S:UScope, unchanged
- The impact is within the kernel/local system security authority and does not cross a VM, IOMMU, or other separate security boundary.
- C:HConfidentiality impact, high
- This is a kernel use-after-free of `struct snd_timer`; stale timer pointers can be dereferenced by later ioctls and may expose reclaimed kernel heap contents or enable broader memory disclosure.
- I:HIntegrity impact, high
- The stale timer pointer is used in paths that take locks and manipulate lists/callback-related state, making kernel heap corruption and control-flow-impacting exploitation defensible.
- A:HAvailability impact, high
- At minimum, dereferencing and locking a freed kernel timer object can trigger a kernel oops, panic, or hang.