[CVE-2026-68153][MODERATE REGULAR] libceph: remove debugfs files before client teardown

[CVE-2026-68153][MODERATE REGULAR] libceph: remove debugfs files before client teardown

[AL-KERNEL]

CVE: CVE-2026-68153
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: libceph: remove debugfs files before client teardown
Commit: fc1010e7e0204ece6cc0f9af4f473e9553535eab
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fc1010e7e0204ece6cc0f9af4f473e9553535eab
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68153
Analysis date: Mon, 10 Aug 2026 13:28:10 -0400
ActionableScore: 4
ActionableScore lower bound: 1
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A local race in libceph client teardown can let a debugfs monmap read run after monc monmap is freed, causing a use after free with likely kernel crash and possible limited stale memory exposure.

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

The original Linux kernel CVE announcement for CVE-2026-68153 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68153

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 REGULAR
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-2026-68153	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A race in libceph client teardown can allow a debugfs monmap read handler to run after ceph_monc_stop has freed monc monmap. This creates a use after free in a local debugfs callback and can plausibly cause a kernel crash or limited exposure of stale kernel memory through the show path. For the CVSS the PR:L is used in the paranoid score because some deployments may expose debugfs access or Ceph client teardown control to a local service account, container root, or reduced capability root rather than only to a full administrator. The issue is not directly network reachable because the trigger is local debugfs access racing client destruction, although it affects systems using Ceph client infrastructure. Impact is at least local denial of service via kernel crash and in worst case may allow limited confidentiality or integrity impact due to UAF memory corruption and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3)	YES	REMOTE RACE UAF NETWORK DEBUGFS LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=4
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended**

## 2. Signal breakdown

Conservative signals:

* Memory corruption, weak primitive: +1. The patch describes a race based UAF in monmap_show after monc->monmap is freed.
* Real lifetime corruption: +1. This is a stale pointer after free during client teardown.
* Reliable kernel crash / strong DoS: +1. A debugfs read racing teardown can plausibly crash the kernel.
* Hard or unreliable race / special timing required: -1. Triggering requires concurrent debugfs access and Ceph client teardown.
* Requires admin/root/CAP in typical deployments: -2. debugfs access and Ceph client teardown are normally administrator controlled.

Paranoid additional interpretation:

* Local unprivileged or reduced privilege trigger concern: +1. Some environments may expose debugfs reads or Ceph lifecycle operations to a service account, container root, or reduced capability root.
* Confidentiality impact plausible: +1. Because the UAF occurs in a debugfs show path, limited stale kernel data exposure is plausible, although not strongly demonstrated.
* No Strong LPE plausibility is awarded. The patch does not show attacker controlled reclaim, object replacement, write after free, type confusion, callback hijack, or refcount takeover.

Race-UAF downgrade applied: this is treated as weak UAF rather than strong corruption because the patch only fixes ordering between debugfs removal and client teardown.

## 3. Reachability analysis

The trigger is local. An attacker needs to read the per client Ceph monmap debugfs file while another path destroys the Ceph client. In normal deployments, debugfs is root accessible and client teardown usually requires administrative control such as unmounting or stopping the Ceph client. Namespaces or containers could reduce the practical privilege barrier only if debugfs or Ceph management is delegated into that environment. The issue is not network reachable by itself, even though it affects Ceph infrastructure.

Call-site confidence: high. The patch directly changes ceph_destroy_client ordering and the commit message identifies monmap_show, ceph_monc_stop, and debugfs_remove lifetime semantics.

## 4. Severity interpretation

This behaves like a local race based UAF with realistic DoS impact and limited possible information exposure. It is not an Important candidate by default because exploitation normally requires privileged local access and no strong LPE primitive is shown. It should not be treated as a pure cleanup either, because the bug is a real UAF in a kernel debugfs callback.

Theoretical memory corruption potential exists due to UAF. Realistic exploitation evidence supports crash or limited stale read, not reliable privilege escalation.

## 5. One-sentence report phrase

A local race in libceph client teardown can let a debugfs monmap read run after monc monmap is freed, causing a use after free with likely kernel crash and possible limited stale memory exposure.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is a real race based UAF, but the conservative score remains low because normal triggering requires privileged debugfs and Ceph teardown access.

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

Patch: libceph: remove debugfs files before client teardown
Commit: fc1010e7e0204ece6cc0f9af4f473e9553535eab
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fc1010e7e0204ece6cc0f9af4f473e9553535eab

Commit description:

ceph_destroy_client() tears down the monitor client before removing
the per-client debugfs files. A concurrent read of the monmap debugfs
file can enter monmap_show() after ceph_monc_stop() has freed
monc->monmap, triggering a use-after-free.

Remove the debugfs files before stopping the OSD and monitor clients.
debugfs_remove() drains active handlers and prevents new accesses, so
the debugfs callbacks can no longer race the rest of client teardown.

Cc: stable@vger.kernel.org
Fixes: 76aa844 ("ceph: debugfs")
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Zhengchuan Liang <zcliangcn@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Assisted-by: Codex:GPT-5.4
Signed-off-by: Douya Le <ldy3087146292@gmail.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Reviewed-by: Viacheslav Dubeyko <slava@dubeyko.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/ceph/ceph_common.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=fc1010e7e0204ece6cc0f9af4f473e9553535eab

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

The original Linux kernel CVE announcement for CVE-2026-68153 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68153

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:H/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 1
  Paranoid ActionableScore: 4

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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).