[CVE-2026-68154][MODERATE 7.0] libceph: reject zero bucket types in crush_decode

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

CVE: CVE-2026-68154
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: libceph: reject zero bucket types in crush_decode
Commit: b8a9fb6bf806f9c4891e71ae1beab0c07c23a877
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b8a9fb6bf806f9c4891e71ae1beab0c07c23a877
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68154
Analysis date: Mon, 10 Aug 2026 16:59:56 -0400
ActionableScore: 6
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A malformed Ceph CRUSH map with bucket type 0 can break mapper invariants and cause a negative OSD weight array index in the kernel Ceph client, making this a network-mediated OOB read and DoS risk when attacker-controlled monitor data can reach the victim.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-68154 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68154

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-2026-68154	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';*CWE-20;CWE-129;CWE-125;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '7';DESCR 'A malformed Ceph CRUSH map can use bucket type 0 even though type 0 is reserved for leaf devices. This breaks the mapper invariant and can make a negative bucket ID be treated as a device ID, which is then passed to is_out and used as a negative index into the OSD weight array. This is an out of bounds read in the kernel Ceph client path and can plausibly cause a kernel crash or incorrect mapping decisions. For the CVSS the PR:N is used because the victim does not need to grant a local account when the attacker can control a Ceph monitor endpoint or tamper with monitor traffic. The issue is network reachable in Ceph deployments where monitor communication is accessible to the attacker, but practical exploitation usually requires a malicious or compromised monitor or a position able to alter CRUSH map delivery. Impact is at least denial of service via kernel crash. For the paranoid score, limited confidentiality and integrity impact are kept because the primitive is an attacker influenced OOB read and mapper state corruption, but no OOB write or arbitrary write primitive is shown.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE SIMPLEFIX NETWORK HARDWARE LINUS KPANIC 	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2
  A malformed CRUSH map is consumed by the kernel Ceph client from Ceph monitor communication. This is network mediated, although practical triggering usually requires a malicious or compromised monitor, or traffic tampering.

* Memory corruption, weak/indirect corruption candidate: +1
  The bug is an unchecked semantic invariant violation that can make a negative bucket ID be interpreted as a device ID, leading to negative indexing into the OSD weight array. This is an OOB read candidate, not an OOB write.

* Reliable kernel crash / strong DoS: +1
  Negative indexing in kernel code can plausibly cause an invalid read, Oops, or kernel crash.

* Important filesystem/storage path: +1
  The affected CRUSH map controls Ceph storage placement and OSD mapping decisions.

* Rare AND difficult-to-reach subsystem/configuration: -1
  Exposure is limited to systems using the in-kernel Ceph client and accepting CRUSH maps from reachable monitors.

Conservative total: 4

Paranoid additional signals:

* Confidentiality impact plausible: +1
  The primitive is an attacker-influenced OOB read in kernel memory. No direct disclosure path is shown, so this remains limited and paranoid only.

* Integrity impact plausible: +1
  Incorrect OSD weight lookup may influence mapper decisions or corrupt logical placement behavior. No write primitive is shown, so this is limited and paranoid only.

Paranoid total: 6

Not awarded:

* No strong memory corruption bonus. The patch shows OOB read / invalid indexing, not OOB write, UAF, double free, arbitrary write, or type confusion.
* No strong LPE bonus. There is no demonstrated reclaim, overwrite, callback control, refcount abuse, or privilege escalation path.
* No Dirty-Pipe-like or page-cache corruption bonus.

## 3. Reachability analysis

The likely attacker model is a malicious or compromised Ceph monitor, or an attacker able to tamper with monitor traffic and deliver a malformed CRUSH map to the kernel Ceph client. No local account on the victim is required in that model, so PR:N is reasonable for CVSS-style triage. The path is not Internet-default exposure, because Ceph monitor networks are normally internal storage or data-center networks. Namespaces and containers do not significantly lower the trigger requirement unless they can cause the host kernel Ceph client to consume attacker-controlled monitor data.

Call-site confidence: high. The commit message explicitly describes the downstream path from crush_decode() to mapper behavior, is_out(), and negative OSD weight array indexing.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because it is network-mediated in Ceph deployments and has a concrete OOB read primitive in kernel code. It is not a clear Important-class memory corruption issue because the patch does not show a write primitive, UAF, object replacement, or practical LPE path. The realistic impact is mainly kernel crash or incorrect storage mapping behavior. The paranoid interpretation keeps limited confidentiality and integrity concern due to attacker-influenced OOB read and mapper invariant violation.

## 5. One-sentence report phrase

A malformed Ceph CRUSH map with bucket type 0 can break mapper invariants and cause a negative OSD weight array index in the kernel Ceph client, making this a network-mediated OOB read and DoS risk when attacker-controlled monitor data can reach the victim.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: network-mediated input plus a concrete OOB read primitive in a kernel storage client path should not be auto-closed, even though the currently supported impact is closer to Actionable Moderate than a proven Important LPE.

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

Patch: libceph: reject zero bucket types in crush_decode
Commit: b8a9fb6bf806f9c4891e71ae1beab0c07c23a877
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b8a9fb6bf806f9c4891e71ae1beab0c07c23a877

Commit description:

CRUSH bucket type 0 is reserved for devices.  The mapper relies on
that invariant and uses type 0 to identify leaf devices.

If crush_decode() accepts a bucket with type 0, a malformed CRUSH map
can make the mapper treat a negative bucket ID as a device and pass it
to is_out(), which then indexes the OSD weight array with a negative
value.

Reject zero bucket types while decoding the CRUSH map so the invalid
state never reaches the mapper.

Cc: stable@vger.kernel.org
Fixes: f24e998 ("ceph: OSD client")
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: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/ceph/osdmap.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=b8a9fb6bf806f9c4891e71ae1beab0c07c23a877

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

The original Linux kernel CVE announcement for CVE-2026-68154 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68154

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:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/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: 6

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).