# CVE-2026-64479: ALSA: seq: Fix uninitialised heap leak in snd_seq_event_dup()

> An unprivileged local user can leak 4 bytes of uninitialized kernel heap memory via the ALSA sequencer interface when specific UMP filtering conditions are met.

- **Severity:** Not scored
- **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:** 25 Jul 2026
- **Updated:** 17 Aug 2026
- **Also known as:** BELL-CVE-2026-64479, DEBIAN-CVE-2026-64479, GHSA-6695-37p4-x7m5, ROOT-OS-UBUNTU-2204-CVE-2026-64479, UBUNTU-CVE-2026-64479

## What is CVE-2026-64479?

CVE-2026-64479 is a vulnerability in Linux, published on 25 Jul 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: Fix uninitialised heap leak in snd_seq_event_dup()

snd_seq_event_dup() copies an incoming event into a pool cell and, in
the UMP-enabled build, clears the trailing cell->ump.raw.extra word that
the memcpy() did not cover.  The guard deciding whether to clear it
compares the copied size against sizeof(cell->event):

	memcpy(&cell->ump, event, size);
	if (size < sizeof(cell->event))
		cell->ump.raw.extra = 0;

For a legacy (non-UMP) event, size == sizeof(struct snd_seq_event) ==
sizeof(cell->event), so the condition is false and the extra word keeps
stale data.  The cell pool is allocated with kvmalloc() (not zeroed) and
cells are reused via a free list, so that word holds uninitialised heap
or leftover event data.

When such a cell is delivered to a UMP client (client->midi_version > 0)
that set SNDRV_SEQ_FILTER_NO_CONVERT -- so the legacy event reaches it
unconverted -- snd_seq_read() reads it out as the larger struct
snd_seq_ump_event and copies the stale word to user space, a 4-byte
kernel heap infoleak to an unprivileged /dev/snd/seq client.

Compare against sizeof(cell->ump) instead, so the trailing word is zeroed
for every event shorter than the UMP cell.

## Which versions are affected by CVE-2026-64479?


## How do I fix CVE-2026-64479?

Apply the vendor's patch.

## Is CVE-2026-64479 being exploited?

There is no known exploitation of CVE-2026-64479 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-64479 and fix it if it is affected.

What it is: CVE-2026-64479 is a vulnerability in Linux, published on 25 Jul 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-2026-64479 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-2026-64479/ (Markdown: https://insights.sbomify.com/CVE-2026-64479/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64479
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64479
- OSV: https://osv.dev/vulnerability/CVE-2026-64479

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64479/
Summaries are generated and may contain mistakes; the official description above is the record.