* [CVE-2026-98116][IMPORTANT] ALSA: pcm: Serialize PCM mmap with buffer reallocation to fix page UAF [ Upstream
@ 2026-09-26 19:07 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-26 19:07 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98116
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: ALSA: pcm: Serialize PCM mmap with buffer reallocation to fix page UAF [ Upstream
Commit: cbc7ec97601d09b74e05e44470fa6b0bcdabf3f5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cbc7ec97601d09b74e05e44470fa6b0bcdabf3f5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98116
Analysis date: Sat, 26 Sep 2026 15:07:45 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98116 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98116
The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.
This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.
The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.
Published priority for this report: IMPORTANT
Manual review required: YES
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98116 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-98116 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;CWE-367;BEST CVSS score: '7';DESCR 'A race in ALSA PCM buffer handling can create a stale writable user mapping of DMA pages that have already been returned to the page allocator. The issue occurs when snd_pcm_mmap_data remaps pages while a concurrent snd_pcm_hw_params or snd_pcm_hw_free operation validates mmap_count and later frees the same buffer. Writable PTEs can remain mapped after the pages are freed and reused, creating a page level use-after-free primitive that may allow corruption of newly allocated kernel or user data. For the CVSS the PR:L because exploitation requires a local process with access to the affected PCM device interface. The race requires timing control so AC:H is appropriate. The issue is not network reachable. Impact includes local denial of service and plausible local privilege escalation due to the stale writable mapping of freed pages.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) YES READ DANGER INIT RACE UAF DMAorINTERRUPT HARDWARE LINUS KPANIC MEMORY KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 4
* Conservative score: 5
* Raw paranoid score: 4
* Paranoid score: 5
* Applied conservative floor: REAL UAF FLOOR 5, 4 -> 5.
* Applied paranoid floor: REAL UAF FLOOR 5, 4 -> 5.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
Positive signals:
* +2 Real UAF or active lifetime violation. `snd_pcm_mmap_data()` installs writable PTEs for PCM DMA-buffer pages without retaining page references. A concurrent buffer reallocation can subsequently free the same pages while the user VMA remains writable.
* +1 Attacker-influenced active-object lifetime manipulation. The relevant PCM client can drive mmap and PCM buffer reallocation operations repeatedly. The patch specifically serializes these two operations because their interleaving creates the stale mapping.
* +1 Weak LPE concern. The resulting primitive is stronger than an ordinary invalid dereference because userspace retains a writable mapping after the mapped pages have returned to the page allocator. This permits post-free modification of subsequently reused page contents, although target selection and controlled reuse are not demonstrated.
Negative signals:
* No hard-race penalty applied. The issue is concurrent, but the commit describes two attacker-drivable PCM operations and provides a reproducer for obtaining the stale writable mapping. The supplied evidence does not establish a rare one-shot or externally uncontrollable timing condition.
* No host-admin penalty applied. Access requirements for the complete affected PCM mmap and reallocation sequence are not fully resolved by the supplied patch. `HostAdminRequired=UNKNOWN` is therefore appropriate.
* No niche-subsystem penalty applied. ALSA PCM is broadly deployed and ordinary audio devices are common. The supplied evidence does not establish a rare hardware-only requirement.
Important non-awarded signals:
* Controlled reclaim or controlled replacement of the freed page by a chosen kernel object is not demonstrated.
* Arbitrary or directed kernel write is not demonstrated.
* Confidentiality impact is not awarded. The patch establishes stale writable access, not read-back of sensitive reused kernel data.
* Integrity impact is not separately awarded. Corruption of a specifically protected kernel object, credential, or file-backed page is not demonstrated.
* Strong LPE plausibility +2 is not awarded. The commit states that local privilege escalation may be possible, but it does not establish attacker-controlled page reuse, target placement, callback influence, or a working escalation chain.
* Reliable kernel crash +1 is not separately awarded. A crash is plausible if a reused page is corrupted, but no direct crash consequence is established as the primary demonstrated result.
* Remote reachability is not established.
3. Reachability analysis
The evaluated attacker is a local process using an affected ALSA PCM device interface. The process must be able to perform PCM buffer operations and mmap the PCM DMA buffer. The patch and commit establish that the relevant mmap and buffer-reallocation operations can race, but they do not fully establish whether every affected deployment grants this complete interface to an ordinary unprivileged account, an audio-group account, a desktop-session account, or only an administrator-managed service.
Accordingly, host-admin-equivalent privilege is not positively established, but below-host-admin reachability is also not fully proven from the supplied evidence. `HostAdminRequired=UNKNOWN` is therefore used. No namespace-specific capability model is involved in the shown path, and there is no evidence that the complete trigger is namespace-scoped. `NamespaceScopedPrivilege=UNKNOWN` is appropriate.
No prior host configuration, sysctl, boot option, special device assignment, or rare hardware prerequisite is identified. The race is likely repeatable for an actor that has PCM mmap and buffer-management access because both relevant operations are part of the same PCM lifetime.
4. Primitive and severity interpretation
The exact primitive is a page-level use-after-free with a stale writable userspace mapping. This is not a simple stale pointer that immediately faults. `remap_pfn_range()` installs writable PTEs for the DMA-buffer pages, and `do_free_pages()` can later return those same pages to the page allocator while the VMA still maps them. The process can therefore write to physical pages after their original PCM-buffer lifetime has ended.
This is active page ownership and lifetime corruption rather than fixed stale storage or an ordinary cleanup-only dereference. The stale mapping is useful after free because it remains writable and can modify data stored in a later allocation of the same pages. However, the supplied evidence does not demonstrate controlled reclaim, chosen kernel-object placement, a callback path, arbitrary read/write, or an actual privilege-escalation exploit.
The issue is therefore `CLASS_B`, not `CLASS_A`. It has meaningful exploitation leverage beyond a crash because the stale VMA provides a post-free write capability. The commit explicitly states that the primitive can be leveraged for local privilege escalation and that a reproducer can create the stale writable mapping. Nevertheless, the complete exploitation chain is not supplied, so the conservative score remains Actionable Moderate rather than directly classifying the issue as Strong Important.
`ImportantCandidate=YES` because page-level writable UAF corruption requires Important-versus-Moderate review. `AutoDowngradeAllowed=NO` because automatically closing the issue as an ordinary race or crash-only ALSA problem would discard a concrete writable post-free page-corruption primitive.
5. One-sentence report phrase
A race between ALSA PCM mmap and buffer reallocation can leave a writable userspace mapping of pages after they are returned to the page allocator, creating a page-level use-after-free primitive that may support local privilege escalation.
6. Manual review recommendation
MANUAL CHECK REQUIRED
The patch establishes a concrete stale writable mapping of freed pages, which is materially stronger than a crash-only UAF, but controlled page reuse and the full local privilege-escalation chain require additional verification.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: ALSA: pcm: Serialize PCM mmap with buffer reallocation to fix page UAF [ Upstream
Commit: cbc7ec97601d09b74e05e44470fa6b0bcdabf3f5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cbc7ec97601d09b74e05e44470fa6b0bcdabf3f5
Changed files:
sound/core/pcm_native.c
Diff excerpt:
Not included in this email. See the upstream URL for the full patch.
Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cbc7ec97601d09b74e05e44470fa6b0bcdabf3f5
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98116 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98116
The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.
The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.
This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.
The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.
Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:
Conservative CVSS vector: Not available
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 7
The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.
CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.
A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.
Conservative ActionableScore: unknown
Paranoid ActionableScore: 5
The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.
For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:
ActionableScore below 5 -> MODERATE REGULAR
ActionableScore 5 or more -> MODERATE 7.0
The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.
There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).
KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.
AL-KERNEL base severity for this report: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT
These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).
Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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