CVE-2026-74388
HighCVSS 7.8Exploitation Probability (EPSS)
Low risk3th percentile - higher than 3% of all known CVEs
Summary
A use-after-free (UAF) vulnerability was found in the Linux kernel's ALSA OSS sequencer subsystem. The issue occurs when SysEx data is processed and the sequencer port is closed before the event is dispatched, leading to use of freed memory. The patch extends the refcounting mechanism to protect resources until the event is dispatched.
Risk Assessment
The vulnerability can lead to kernel memory corruption, potentially causing system crashes or privilege escalation. The attack requires access to the OSS sequencer interface, which may be exploited locally by an unprivileged user.
Recommendation
Immediately update the Linux kernel to a patched version. If updating is not possible, restrict access to OSS sequencer devices (e.g., via file permissions) and monitor the system for unusual behavior.
Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: ALSA: seq: oss: Fix UAF at handling events with embedded SysEx data 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 (?:?)