# CVE-2026-74388: ALSA: seq: oss: Fix UAF at handling events with embedded SysEx data

> A use-after-free in the Linux kernel ALSA OSS sequencer allows local attackers to execute arbitrary code or escalate privileges via concurrent port closure.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **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:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 21 Oct 2026
- **Also known as:** BELL-CVE-2026-74388, DEBIAN-CVE-2026-74388, GHSA-qr2g-fp68-m7q5, UBUNTU-CVE-2026-74388

## What is CVE-2026-74388?

CVE-2026-74388 is a high-severity use after free vulnerability in Linux, published on 15 Aug 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: 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 (?:?)

## Which versions are affected by CVE-2026-74388?


## How do I fix CVE-2026-74388?

Apply the vendor's patch.

## Is CVE-2026-74388 being exploited?

There is no known exploitation of CVE-2026-74388 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74388 and fix it if it is affected.

What it is: CVE-2026-74388 is a high-severity use after free vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-74388 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-74388/ (Markdown: https://insights.sbomify.com/CVE-2026-74388/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74388
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74388
- OSV: https://osv.dev/vulnerability/CVE-2026-74388

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74388/
Summaries are generated and may contain mistakes; the official description above is the record.