[CVE-2026-99039][MODERATE 7.0] memstick: core: wait for request completion before freeing card

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-99039
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: memstick: core: wait for request completion before freeing card
Commit: c3ab92542475d59ae685cbb294e70ca4d0ba38e9
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c3ab92542475d59ae685cbb294e70ca4d0ba38e9
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99039
Analysis date: Tue, 27 Oct 2026 01:36:33 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
A delayed MemoryStick request can outlive and write into its freed card object, causing a physically triggered, constrained slab UAF write and plausible kernel crash.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-99039 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99039

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: MODERATE 7.0
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-2026-99039	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-99039 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=MODERATE_KPANIC RESULT=SAME V39_AEGIS_ONE_STEP_UP=MODERATE->MODERATE_KPANIC (final reconciliation agrees; DECISION: both MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:P/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '6.4';DESCR 'A memstick request can remain active after the old 500 ms completion timeout while memstick_alloc_card frees the card object. A host worker such as rtsx_usb_ms_handle_req can later write through host req data into the freed slab object, providing a confirmed use-after-free write and a direct kernel memory corruption primitive. For the CVSS the PR:N value reflects triggering through a malicious or faulty physically attached device without requiring an authenticated software account. AC:H reflects the timing and heap reuse conditions needed for security relevant corruption beyond a simple crash. Impact is at least denial of service and the confirmed stale write may permit confidentiality or integrity impact if the freed allocation is reused, although an arbitrary write or reliable privilege escalation is not demonstrated. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 6.4 and the production ActionableScore returned 3 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage IMPORTANT to MODERATE_KPANIC because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. final reconciliation stage MODERATE to MODERATE_KPANIC because the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 2.4 and ActionableScore 4 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	MAYBE	WRITE OOB DANGER UAF HARDWARE LINUS SYZBOT  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 KPANIC V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED	-	-	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=3
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=REQUIRED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 3.
* Conservative score: 3; no floor or cap applied.
* Raw paranoid score: 3.
* Paranoid score: 3; generic slab reuse does not justify another point.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +2 — Real UAF: the 500 ms timeout permits `kfree(card)` while the asynchronous host request still references storage inside `card`.
* +1 — Constrained post-free overwrite: `ms_read_bytes()` performs a confirmed one-byte write into the freed slab allocation. The destination follows the stale request buffer and is not an arbitrary target.
* +1 — Plausible kernel crash/strong DoS from writing through a dangling request buffer.
* +1 — Device-mediated external influence: a delayed malicious or faulty attached device can plausibly keep the request active beyond the timeout.
* -2 — Physical/specialized hardware requirement: the demonstrated path requires MemoryStick host/controller hardware and an attached device.

Not awarded: controlled reclaim, selected adjacent victim, arbitrary write, callback control, disclosure, LPE, or C/I impact. No extra availability point duplicates the same crash. B5-R does not apply: there is no retry-accumulated index or heap OOB sequence. B3/B4 pending profiles are unrelated.

3. Reachability analysis

The grounded attacker model is a malicious or faulty physically attached MemoryStick-side device interacting with a supported host controller. No host UID 0, capability, namespace, or prior privileged software configuration is shown as necessary once the hardware is present. The timeout ordering is asynchronous, but the UAF does not require a narrow race: request delay beyond 500 ms followed by completion is sufficient. Exploit-relevant slab reuse remains timing-dependent.

4. Primitive and severity reading

This is fixed asynchronous stale storage, not an attacker-replaced active structured object. The card is freed while the controller worker retains an in-flight request pointer, and later completion writes into that freed allocation. This is CLASS_B lifetime corruption with a confirmed constrained post-free write. Crash and slab corruption are supported; useful reclaimed-object corruption is unproven. The specialized physical trigger and lack of target selection keep it below an Important candidate, so downgrade after review remains permissible.

5. One-sentence report phrase

A delayed MemoryStick request can outlive and write into its freed card object, causing a physically triggered, constrained slab UAF write and plausible kernel crash.

6. Manual review advice

MANUAL CHECK REQUIRED

Confirm device control over returned bytes, write extent, allocator reuse behavior, and whether any controller path enables broader post-free corruption.

7. Call-site confidence

Call-site confidence: high

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: memstick: core: wait for request completion before freeing card
Commit: c3ab92542475d59ae685cbb294e70ca4d0ba38e9
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c3ab92542475d59ae685cbb294e70ca4d0ba38e9

Commit description:

In memstick_alloc_card() and memstick_set_rw_addr(),
wait_for_completion_timeout() is used to wait for device identification
and address configuration requests to complete.

The memstick subsystem does not provide an abort or cancellation
callback in struct memstick_host for in-flight requests. If
wait_for_completion_timeout() expires (for instance, when a USB transfer
or command retry is delayed), memstick_alloc_card() returns an error and
frees the memstick_dev structure via kfree(card).

However, the host controller driver (such as rtsx_usb_ms) is still
running the request asynchronously in worker context. When the transfer
eventually finishes, the driver writes into host->req->data, which
points to memory inside the already freed card structure. This leads to
a KASAN slab-use-after-free write:

  BUG: KASAN: slab-use-after-free in ms_read_bytes+0x8fe/0x990
  Write of size 1 at addr ffff88813c188079 by task kworker/1:5/5239
  Workqueue: events rtsx_usb_ms_handle_req
  Call Trace:
   ms_read_bytes+0x8fe/0x990 drivers/memstick/host/rtsx_usb_ms.c:450
   rtsx_usb_ms_issue_cmd drivers/memstick/host/rtsx_usb_ms.c:477 [inline]
   rtsx_usb_ms_handle_req+0x557/0x1a00 drivers/memstick/host/rtsx_usb_ms.c:531
   process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396
   worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
   kthread+0x373/0x450 kernel/kthread.c:436

  Allocated by task 1662:
   memstick_alloc_card drivers/memstick/core/memstick.c:383 [inline]
   memstick_check+0x2c1/0x10d0 drivers/memstick/core/memstick.c:452
   process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396

  Freed by task 1662:
   kfree+0x20c/0x650 mm/slub.c:6792
   memstick_alloc_card drivers/memstick/core/memstick.c:420 [inline]
   memstick_check+0x72b/0x10d0 drivers/memstick/core/memstick.c:452
   process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396

Host controller drivers (rtsx_usb_ms, jmb38x_ms, tifm_ms, r592) already
implement their own hardware and bus timeouts, and callers in
mspro_block and ms_block already rely on wait_for_completion()
unconditionally.

Replace wait_for_completion_timeout() with wait_for_completion() in
memstick_set_rw_addr() and memstick_alloc_card() so that the card
structure is never freed while an asynchronous request is in flight.

Fixes: baf8532 ("memstick: initial commit for Sony MemoryStick support")
Reported-by: syzbot+ccffdf05833ebdaeae70@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=ccffdf05833ebdaeae70
Cc: stable@vger.kernel.org
Signed-off-by: Raj Ojha <rajojha047@gmail.com>
Signed-off-by: Ulf Hansson <ulfh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/memstick/host/rtsx_usb_ms.c
  kernel/workqueue.c
  kernel/kthread.c
  drivers/memstick/core/memstick.c
  mm/slub.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=c3ab92542475d59ae685cbb294e70ca4d0ba38e9

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-99039 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99039

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: AV:P/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:P/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.4

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: 3

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: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).