CVE-2026-98116
Received Received - Intake

Use-After-Free in Linux Kernel ALSA PCM Subsystem

Publication date: 2026-09-25

Last updated on: 2026-09-25

Assigner: kernel.org

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.

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Meta Information

Published
2026-09-25
Last Modified
2026-09-25
Generated
2026-09-25
AI Q&A
2026-09-25
EPSS Evaluated
N/A
NVD
CVE-2026-98116
EUVD
EUVD-2026-86947

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *

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Exploitability

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This is a use-after-free vulnerability in the Linux kernel's ALSA PCM subsystem. It occurs when a concurrent mmap() operation accesses a buffer that is being reallocated. The issue arises because buffer reallocation and mmap operations are not properly synchronized, allowing a stale writable mapping of freed pages to persist. This can lead to local privilege escalation.

Detection Guidance

This vulnerability is specific to the Linux kernel's ALSA PCM subsystem and requires kernel-level detection. Check if your kernel version includes the fix by running uname -a and comparing against patched versions. Monitor system logs for ALSA-related errors or crashes, particularly during audio buffer operations.

Impact Analysis

This vulnerability allows an attacker with local access to escalate privileges on a vulnerable system. By exploiting the race condition, an attacker could gain root-level access, potentially leading to full system compromise. It does not require network access, only local execution.

Mitigation Strategies

Apply the latest kernel security updates from your Linux distribution. If immediate patching is not possible, disable ALSA PCM functionality by blacklisting the snd-pcm module or restricting access to audio devices. Monitor vendor advisories for kernel updates addressing this issue.

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