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CVE-2026-74388
ALSA: seq: oss: Fix UAF at handling events with embedded SysEx data
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem sound/core. Debian urgency: not yet assigned.
Debian does not build this code. The per-release build detail is under "Where it lives" below.
What to do, per Debian release
Debian's own status for CVE-2026-74388 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 | vulnerable | 6.1.190-1 | No fix published anywhere yet, neither in Debian nor upstream for the series bookworm tracks. Watch the Debian tracker page for this CVE. Advisories for bookworm have historically landed a median of 23 days after publication. |
| Debian 13trixie | vulnerable | 6.12.113-1 | No fix published anywhere yet, neither in Debian nor upstream for the series trixie tracks. Watch the Debian tracker page for this CVE. Advisories for trixie have historically landed a median of 11 days after publication. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
The OSS sequencer processes the input MIDI bytes into a sequencer event to be dispatched later (in snd_seq_oss_midi_putc() called from snd_seq_oss_process_event()). When it's a SysEx data, the event record contains data.ext.ptr pointer to the original SysEx bytes, and the referred data is copied into the pool afterwards at dispatching. The problem is that, if the sequencer port gets closed concurrently before the dispatch, the OSS sequencer core also releases the resources (in snd_seq_oss_midi_check_exit_port()), while the pending event may hold a stale pointer, eventually leading to a UAF at a later dispatch. Fortunately, there is already a refcounting mechanism (snd_use_lock_t) for the OSS MIDI device access, and for addressing the issue above, we just need to extend the refcount until the event gets dispatched. This patch extends snd_seq_oss_process_event() to give back the refcount object, which is in turn released after calling the sequencer dispatcher with the given event in the caller side. According to the original report, KASAN report as below: KASAN slab-use-after-free in snd_seq_event_dup+0x40c/0x470 RIP: 0033:0x7f2cb66a6340 Read of size 6 Call trace: dump_stack_lvl+0x73/0xb0 (?:?) print_report+0xd1/0x650 (?:?) srso_alias_return_thunk+0x5/0xfbef5 (?:?) __virt_addr_valid+0x1a7/0x340 (?:?) kasan_complete_mode_report_info+0x64/0x200 (?:?) kasan_report+0xf7/0x130 (?:?) snd_seq_event_dup+0x40c/0x470 (?:?) kasan_check_range+0x10c/0x1c0 (?:?) __asan_memcpy+0x27/0x70 (?:?) snd_seq_event_dup+0x9/0x470 (?:?) snd_seq_client_enqueue_event+0x139/0x240 (?:?) _raw_spin_unlock_irqrestore+0x4b/0x60 (?:?) snd_seq_kernel_client_enqueue+0x102/0x120 (?:?) snd_seq_oss_write+0x416/0x4e0 (?:?) apparmor_file_permission+0x20/0x30 (?:?) odev_write+0x3b/0x60 (?:?) vfs_write+0x1ce/0x850 (?:?) lock_release+0xc8/0x2a0 (?:?) __kasan_check_write+0x18/0x20 (?:?) __mutex_unlock_slowpath+0x129/0x510 (?:?) ksys_write+0xe1/0x180 (?:?) mutex_unlock+0x16/0x20 (?:?) odev_ioctl+0x65/0xc0 (?:?) __x64_sys_write+0x46/0x60 (?:?) x64_sys_call+0x7d/0x20d0 (?:?) do_syscall_64+0xc1/0x360 (arch/x86/entry/syscall_64.c:87) entry_SYSCALL_64_after_hwframe+0x77/0x7f (?:?)
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/seq/oss/seq_oss_event.c
sound/core/seq/oss/seq_oss_event.h
sound/core/seq/oss/seq_oss_ioctl.c
sound/core/seq/oss/seq_oss_midi.c
sound/core/seq/oss/seq_oss_midi.h
sound/core/seq/oss/seq_oss_rw.c
- What this is
- SOUNDMAINTAINERS section matched on sound/ · linux-sound@vger.kernel.org · Maintained
- Kernel module
- none to look for. The file would have gone into snd_seq_oss, and Debian does not compile it into that module, so finding snd_seq_oss in lsmod would say nothing about this CVE.
Check it on the machine
grep -wE 'CONFIG_SND|CONFIG_SND_SEQUENCER|CONFIG_SND_SEQUENCER_OSS' /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.
Show whether Debian builds this, per release
Debian does not build this code. In 4 releases below, every kernel flavour Debian publishes has the switch off, so the vulnerable file is compiled into no kernel binary Debian ships.
- bookworm, trixie, forky, sidn
- n
- not enabled on any flavour - this release does not build the code
- Build switches
- CONFIG_SND, CONFIG_SND_SEQUENCER, CONFIG_SND_SEQUENCER_OSS
- 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
- 2026-08-15 (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
- 0.12%, higher than 1.9% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- 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 |
|---|---|---|
| 2.6.12 | 6.18.40 | 6dc781778b59 |
| 2.6.12 | 7.1.5 | 7aad70cabd8f |
| 2.6.12 | 7.2 | 7c349b4f2a60 |
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 only via local OSS sequencer character devices (/dev/sequencer, /dev/music) through write(2) or SNDCTL_SEQ_OUTOFBAND ioctl into snd_seq_oss_write(); there is no network, Bluetooth, or physical-device input path to this OSS sequencer code.
- AC:LAttack complexity, low
- The attacker controls both sides of the race: one thread streams SysEx MIDI bytes (SEQ_MIDIPUTC) while another concurrently deletes the backing ALSA sequencer port via /dev/snd/seq or triggers PORT_EXIT teardown, and the window is freely repeatable.
- PR:LPrivileges required, low
- Exploitation requires only a local unprivileged account with access to OSS sequencer and ALSA sequencer device nodes, routinely granted via the audio group or seat ACLs on desktop, studio, and kiosk systems; no capability or init-namespace root is checked on this path.
- UI:NUser interaction, none
- The attacker's own process(es) perform the SysEx write and concurrent port-close/delete sequence; no separate victim action such as opening files, mounting filesystems, or plugging in hardware is required beyond the attacker's own device access.
- S:UScope, unchanged
- The use-after-free corrupts kernel heap memory within the same kernel security authority, enabling local privilege escalation or denial of service, but does not cross a VM, IOMMU, or sandbox security boundary.
- C:HConfidentiality impact, high
- This is a slab use-after-free where snd_seq_event_dup() memcpy-reads from a freed MIDI coder buffer (KASAN: read of size 6); UAF on kernel heap objects enables controlled reuse and arbitrary kernel memory disclosure via heap grooming.
- I:HIntegrity impact, high
- Freed seq_oss_midi/coder objects can be reallocated and corrupted through continued SysEx traffic, providing standard kernel heap overwrite primitives that can be leveraged for arbitrary write and local privilege escalation.
- A:HAvailability impact, high
- The UAF is observed as a KASAN slab-use-after-free during event enqueue and reliably causes kernel oops or panic on the vulnerable path; even without full exploitation, triggering the bug causes high availability impact.