[CVE-2026-52930][MODERATE 7.0] ipc/shm: serialize orphan cleanup with shm_nattch updates

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

CVE: CVE-2026-52930
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ipc/shm: serialize orphan cleanup with shm_nattch updates
Commit: b1e9aef48e4d8a0c1b54fb913077b0824ed7d650
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b1e9aef48e4d8a0c1b54fb913077b0824ed7d650
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52930
Analysis date: Wed, 24 Jun 2026 04:46:50 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum**:: Actionable Moderate at minimum. Not enough evidence for Strong Important as the main classification.
Manual review required: YES

Summary:
A local race in SysV shared memory orphan cleanup can allow shm_destroy_orphaned to destroy a segment based on stale shm_nattch state while another task is attaching to it, creating a UAF-like lifetime corruption risk with realistic DoS impact and possible privilege-escalation concern.

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

The original Linux kernel CVE announcement for CVE-2026-52930 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52930

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-52930	MODERATE	CHECK	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-362;*CWE-416;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'SysV shared memory orphan cleanup can race with concurrent attach updates because shm_destroy_orphaned walks the idr under the namespace rwsem while shm_nattch can be changed under shm_perm.lock without that rwsem. The stale check can make cleanup decide that an orphaned segment is unused before the object lock is taken, and a concurrent attach can then leave the kernel destroying a segment that is becoming referenced. This is a local race in the shm lifecycle and the main confirmed impact is denial of service via crash or corrupted object lifetime state. For the CVSS the PR:L is used because a local unprivileged process can normally create or attach SysV shm objects in its IPC namespace, although reliable triggering depends on the orphan cleanup path and timing. The issue is not network reachable. For the paranoid score, the same race and UAF class is treated as potentially affecting confidentiality and integrity, because destroying a shared memory object while attach state changes may leave stale references and should be manually reviewed for privilege escalation risk.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	LOCK SIMPLEFIX IMPROVEONLY TEST  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: Actionable Moderate at minimum. Not enough evidence for Strong Important as the main classification.

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1
  SysV shared memory operations such as shmget and shmat are normally reachable by local unprivileged users inside an IPC namespace.

* Memory corruption, weak/indirect corruption candidate: +1
  The bug is a race in object lifetime decisions. The stale shm_may_destroy check can destroy a segment after shm_nattch changed, but the patch does not show controlled reclaim, overwrite, callback dispatch, or type confusion.

* Real lifetime corruption: +1
  The fix moves the destroy eligibility check under shm_perm.lock, which indicates a real lifetime/refcount synchronization issue.

* Reliable kernel crash / strong DoS concern: +1
  Destroying a shared memory segment while attach state changes can plausibly cause stale references, corrupted IPC object state, or kernel crash.

* Broad/default/common subsystem: +1
  SysV IPC shared memory is a standard Linux kernel facility and not a rare driver path.

Negative signal:

* Hard or unreliable race / special timing required: -1
  Triggering requires a race between orphan cleanup and concurrent attach/nattch updates, plus the segment must be in the orphan cleanup path.

Conservative total: 4.

Paranoid adjustment:

* The paranoid score does not apply the timing penalty because repeated local shm create/attach/exit activity may make the race practically reachable under stress.
  Paranoid total: 5.

No strong LPE bonus is counted because the patch does not demonstrate attacker-controlled reclaim, writable UAF, object replacement, function-pointer reachability, refcount takeover, or arbitrary write.

## 3. Reachability analysis

A local user can normally interact with SysV shared memory, including creating and attaching segments, subject to normal IPC namespace and resource limits. The vulnerable cleanup path depends on orphaned shared memory segment cleanup, so reliable triggering likely requires arranging creator exit and concurrent attach activity around shm_destroy_orphaned. IPC namespaces can make the interface available to containerized users, but the impact is expected to remain within the kernel instance if the race corrupts shared kernel IPC state. The issue is not network reachable. It is default kernel functionality rather than a rare device-specific configuration, but exploitation requires timing.

## 4. Severity interpretation

This behaves above an ordinary Moderate because it is a real local kernel object lifetime race in a common IPC subsystem. The realistic demonstrated impact is local DoS or corrupted shared memory object lifetime state. Theoretical privilege escalation cannot be excluded because destroying an object while it is concurrently becoming referenced is a UAF-like pattern, but the patch does not show a strong exploitation primitive. Therefore it is best treated as Actionable Moderate at minimum, with manual review required, rather than auto-closed as low-risk.

## 5. One-sentence report phrase

A local race in SysV shared memory orphan cleanup can allow shm_destroy_orphaned to destroy a segment based on stale shm_nattch state while another task is attaching to it, creating a UAF-like lifetime corruption risk with realistic DoS impact and possible privilege-escalation concern.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the bug is a race in shared-memory object lifetime management and has a plausible UAF-like failure mode, even though the patch does not prove a controlled privilege-escalation primitive.

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

Patch: ipc/shm: serialize orphan cleanup with shm_nattch updates
Commit: b1e9aef48e4d8a0c1b54fb913077b0824ed7d650
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b1e9aef48e4d8a0c1b54fb913077b0824ed7d650

Commit description:

shm_destroy_orphaned() walks the shm idr under shm_ids(ns).rwsem, but that
does not serialize all fields tested by shm_may_destroy().  In particular,
shm_nattch is updated while holding shm_perm.lock, and attach paths can do
that without holding the rwsem.

Do not decide that an orphaned segment is unused before taking the object
lock.  Move the shm_may_destroy() check under shm_perm.lock, matching the
other destroy paths, and unlock the segment when it no longer qualifies
for removal.

Link: https://lore.kernel.org/9d97cc1031de2d0bace0edf3a668818aa2f4eca6.1777410234.git.zylzyl2333@gmail.com
Fixes: 4c677e2 ("shm: optimize locking and ipc_namespace getting")
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Signed-off-by: Yilin Zhu <zylzyl2333@gmail.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jeongjun Park <aha310510@gmail.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Liam Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Serge Hallyn <sergeh@kernel.org>
Cc: Vasiliy Kulikov <segoon@openwall.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Serge Hallyn <serge@hallyn.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  ipc/shm.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=b1e9aef48e4d8a0c1b54fb913077b0824ed7d650

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

The original Linux kernel CVE announcement for CVE-2026-52930 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52930

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:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  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: 4
  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: 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).