CVE-2026-90207 ALSA: seq: midi: Serialize input teardown with event_input
A race condition in the Linux kernel ALSA MIDI driver causes a null pointer dereference, leading to a system crash.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-90207?
CVE-2026-90207 is a high-severity vulnerability in Linux, published on 17 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
ALSA: seq: midi: Serialize input teardown with event_input
snd_midi_input_event() must not be running while a rawmidi substream is closing, since this can lead to the trigger state becoming out-of-step through this sequence in snd_rawmidi_input_trigger():
snd_rawmidi_input_trigger(up=0) snd_midi_input_event() -> snd_rawmidi_kernel_read() -> snd_rawmidi_input_trigger(up=1) -> cancel_work_sync()
which ends with the underlying device being active unexpectedly.
When this is called from close_substream(), further input can re-trigger the input event leaving it running after rawmidi_release_priv() has set rfile->rmidi to NULL which leads to:
Unable to handle kernel NULL pointer dereference at virtual address 00000000000000b0 Call trace: snd_midi_input_event+0x3c/0x134 [snd_seq_midi] (P) snd_rawmidi_input_event_work+0x1c/0x2c process_one_work+0x150/0x3a4 worker_thread+0x190/0x318
Apply a similar approach to commit ef7607ab1c8ad ("ALSA: seq: midi: Serialize output teardown with event_input") which fixed the same issue in the output direction, but updated to use RCU following Takashi Iwai's proposed follow-on patch [1].
With this change in place, midisynth_unsubscribe() clears the input file so snd_midi_input_event() will not re-trigger the stream and will be quiesced by the cancel_work_sync() in snd_rawmidi_input_trigger().
[1] https://lore.kernel.org/linux-sound/[email protected]/
Which versions are affected by CVE-2026-90207?
How do I fix CVE-2026-90207?
Apply the vendor's patch.
Is CVE-2026-90207 being exploited?
There is no known exploitation of CVE-2026-90207 in the wild and no public exploit code.
Sources
Also known as AZL-102687, BELL-CVE-2026-90207, DEBIAN-CVE-2026-90207, GHSA-hhf3-44mr-39mw, UBUNTU-CVE-2026-90207.