Description
In the Linux kernel, the following vulnerability has been resolved:

ALSA: pcm: Serialize PCM mmap with buffer reallocation to fix page UAF

snd_pcm_hw_params() and snd_pcm_hw_free() guard buffer reallocation
with an mmap_count check performed under the PCM stream lock, but the
lock is released long before the buffer is actually freed:
snd_pcm_sync_stop(), constraint refinement and do_free_pages() all
happen in between. snd_pcm_mmap_data(), on the other hand, takes no
lock at all: it validates against the old buffer's state and
dma_bytes, remaps its pages into the VMA, and only then increments
mmap_count.

A concurrent mmap() can therefore slip in between the check and the
free. remap_pfn_range() installs writable PTEs for the old buffer's
pages without taking page references, and the subsequent
do_free_pages() returns those pages to the page allocator while the
VMA still maps them. This leaves a stale, writable mapping of freed
pages: a page-level use-after-free that can be leveraged for local
privilege escalation.

Make snd_pcm_mmap_data() participate in the buffer-access scheme
introduced for hw_params/hw_free: acquire runtime->buffer_accessing
before validating and remapping, and release it afterwards. Buffer
reallocation already fails with -EBUSY while accessors are active,
and the mmap side now fails with -EBUSY while a reallocation is in
progress, so the validate/remap sequence and the check/free sequence
can no longer interleave.

A reproducer that turns this race into a stale writable mapping of
the freed DMA buffer pages is available on request.
Published: 2026-09-25
Score: 7.8 High
EPSS: n/a
KEV: No
Impact: Privilege Escalation
Action: Immediate Patch
AI Analysis

Impact

A race condition exists in the ALSA PCM interface of the Linux kernel where concurrent memory-mapped operations can interleave with buffer deallocation. During this race a page that has been freed is still mapped as writable, creating a page-level use‑after‑free. An attacker can exploit this stale writable mapping to execute arbitrary code or modify system memory, thereby achieving local privilege escalation.

Affected Systems

All Linux kernel versions lacking the ALSA PCM mmap page‑UAF fix, regardless of vendor. The vulnerability is present in the kernel’s ALSA subsystem and applies to any system that allows a process to perform PCM mmap operations. No product or version exclusions are listed; users should consult kernel release notes for the commit that introduced the fix.

Risk and Exploitability

The vulnerability permits local exploitation only; a privileged user or a process that can invoke PCM mmap can race with the buffer free routine. No EPSS score is available and the issue is not listed in the CISA KEV catalog, suggesting a low to moderate likelihood of widespread exploitation. For systems that remain at risk, the high potential for local privilege escalation means that the CVSS impact should be viewed as high, and any kernel update that patches the race should be prioritized.

Generated by OpenCVE AI on September 25, 2026 at 11:41 UTC.

Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

  • Upgrade the Linux kernel to a version that contains the ALSA PCM mmap page‑UAF fix, such as the commit referenced in the advisory
  • Verify that the updated kernel implements the new snd_pcm_mmap_data protection and that the buffer‑access synchronization is active
  • If a kernel upgrade cannot be performed immediately, restrict access to ALSA PCM devices for untrusted processes or disable PCM mmap functionality where possible

Generated by OpenCVE AI on September 25, 2026 at 11:41 UTC.

Tracking

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Advisories

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History

Fri, 25 Sep 2026 15:00:00 +0000

Type Values Removed Values Added
Metrics cvssV3_1

{'score': 7.8, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'}


Fri, 25 Sep 2026 12:00:00 +0000

Type Values Removed Values Added
Weaknesses CWE-362
CWE-416

Fri, 25 Sep 2026 10:45:00 +0000

Type Values Removed Values Added
Description In the Linux kernel, the following vulnerability has been resolved: ALSA: pcm: Serialize PCM mmap with buffer reallocation to fix page UAF snd_pcm_hw_params() and snd_pcm_hw_free() guard buffer reallocation with an mmap_count check performed under the PCM stream lock, but the lock is released long before the buffer is actually freed: snd_pcm_sync_stop(), constraint refinement and do_free_pages() all happen in between. snd_pcm_mmap_data(), on the other hand, takes no lock at all: it validates against the old buffer's state and dma_bytes, remaps its pages into the VMA, and only then increments mmap_count. A concurrent mmap() can therefore slip in between the check and the free. remap_pfn_range() installs writable PTEs for the old buffer's pages without taking page references, and the subsequent do_free_pages() returns those pages to the page allocator while the VMA still maps them. This leaves a stale, writable mapping of freed pages: a page-level use-after-free that can be leveraged for local privilege escalation. Make snd_pcm_mmap_data() participate in the buffer-access scheme introduced for hw_params/hw_free: acquire runtime->buffer_accessing before validating and remapping, and release it afterwards. Buffer reallocation already fails with -EBUSY while accessors are active, and the mmap side now fails with -EBUSY while a reallocation is in progress, so the validate/remap sequence and the check/free sequence can no longer interleave. A reproducer that turns this race into a stale writable mapping of the freed DMA buffer pages is available on request.
Title ALSA: pcm: Serialize PCM mmap with buffer reallocation to fix page UAF
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References

Subscriptions

Linux Linux Kernel
cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-09-25T14:42:08.633Z

Reserved: 2026-09-25T10:25:14.317Z

Link: CVE-2026-98116

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-09-25T11:17:42.780

Modified: 2026-09-25T15:18:06.437

Link: CVE-2026-98116

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-09-25T12:30:08Z

Weaknesses
  • CWE-362

    Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

  • CWE-416

    Use After Free