[CVE-2026-68158][MODERATE 7.0] libceph: Fix multiplication overflow in decode_new_up_state_weight()

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

CVE: CVE-2026-68158
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: libceph: Fix multiplication overflow in decode_new_up_state_weight()
Commit: 05c90e059269f087becfcce23348496085835c29
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=05c90e059269f087becfcce23348496085835c29
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68158
Analysis date: Mon, 10 Aug 2026 18:14:29 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A multiplication overflow in libceph decode_new_up_state_weight() can make CEPH_MSG_OSD_MAP bounds validation use an incorrect length, allowing a malicious or corrupted OSD map from a trusted Ceph control path to trigger out-of-bounds reads and likely kernel DoS.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-68158 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68158

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-2026-68158	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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-190;CWE-125;*CWE-20;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A multiplication overflow in libceph decode_new_up_state_weight() can make the bounds check for the new_state part of a CEPH_MSG_OSD_MAP message use a smaller length than the real encoded data. A malicious or corrupted OSD map can then make the kernel decoder advance with an invalid size and perform out of bounds reads while parsing the message. For the CVSS the PR:N is used for the paranoid score because no privileges are needed on the victim once an attacker can supply an accepted Ceph OSD map message. The issue is network delivered through the Ceph control path, but practical exploitation usually requires a malicious or compromised Ceph monitor or a trusted internal Ceph network position. Impact is at least denial of service via kernel crash. In the worst still defensible interpretation, limited confidentiality or integrity impact may be possible due to out of bounds reads and parser state confusion, so manual review is recommended.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE WRITE OOB DANGER SIMPLEFIX NETWORK LINUS KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

* Remote reachable / network-triggerable: +2
  CEPH_MSG_OSD_MAP is received through the Ceph control path. Practical triggering requires the victim Ceph client to accept a malicious or corrupted OSD map, usually from a malicious or compromised monitor or from an attacker able to tamper with trusted Ceph network traffic.

* Reliable kernel crash / strong DoS: +1
  The commit explicitly describes out-of-bounds memory accesses during decode. The most realistic impact is kernel Oops or crash while parsing the malformed OSD map.

* Important filesystem/storage path: +1
  libceph OSD map parsing is part of the Ceph storage client control plane. A crash here can affect mounted CephFS or RBD users.

* Weak/indirect corruption candidate: +1 for paranoid score only
  The concrete primitive shown is integer overflow leading to out-of-bounds reads, not OOB write or UAF. However, because this is a network-delivered kernel parser that advances decode state based on attacker-influenced length fields, manual review is justified for possible parser state confusion. This does not justify treating it as strong memory corruption.

Not applied:

* Strong memory corruption: +0
  The patch shows OOB reads, not OOB write, UAF, double free, arbitrary write, or type confusion.

* Privilege escalation plausible: +0
  No concrete LPE primitive is shown.

* Confidentiality / integrity impact: +0 conservative
  OOB read exists, but no clear user-visible disclosure or controlled integrity corruption path is shown in the patch.

## 3. Reachability analysis

A remote party can influence the vulnerable input only if it can supply an accepted Ceph OSD map to the client. In normal deployments this usually means a malicious or compromised Ceph monitor, or a trusted internal network attacker capable of tampering with Ceph control traffic. No local privileges are required on the victim once such a message is accepted. This is not a general Internet-facing kernel path, but it is network-delivered in Ceph deployments and should not be treated as a purely local issue.

Call-site confidence: medium. The provided patch shows the vulnerable decoder and malformed length handling, but not all downstream decode users.

## 4. Severity interpretation

This behaves like an actionable Moderate issue rather than ordinary Low or auto-close Moderate. The realistic impact is DoS through kernel crash from malformed Ceph protocol data. The theoretical risk is higher than a simple NULL dereference because the bug is an integer overflow in a kernel network/storage parser that can cause OOB reads and decode state confusion. However, the patch does not support classifying it as Important by default because there is no demonstrated write primitive, UAF, reclaim primitive, arbitrary memory corruption, or privilege escalation path.

## 5. One-sentence report phrase

A multiplication overflow in libceph decode_new_up_state_weight() can make CEPH_MSG_OSD_MAP bounds validation use an incorrect length, allowing a malicious or corrupted OSD map from a trusted Ceph control path to trigger out-of-bounds reads and likely kernel DoS.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: network-delivered kernel parser input plus integer overflow and OOB read risk. The likely impact is DoS, but parser state confusion in a storage control path is important enough to avoid automatic closure.

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

Patch: libceph: Fix multiplication overflow in decode_new_up_state_weight()
Commit: 05c90e059269f087becfcce23348496085835c29
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=05c90e059269f087becfcce23348496085835c29

Commit description:

If a message of type CEPH_MSG_OSD_MAP contains a (maliciously) corrupted
osdmap, out-of-bounds memory accesses may occur in
decode_new_up_state_weight(). This happens because the bounds check for
the new_state part is based on calculating its length depending on a len
value read from the incoming message. This calculation may overflow
leading to an incorrect bounds check. Subsequently, out-of-bounds reads
may occur when decoding this part.

This patch switches the multiplication to use check_mul_overflow() to
abort processing the osdmap if an overflow occurred. Therefore,
osdmaps/messages containing large values for len that result in a
multiplication overflow are treated as invalid.

[ idryomov: rename new_state_len -> new_state_item_size, formatting ]

Cc: stable@vger.kernel.org
Fixes: 930c532 ("libceph: apply new_state before new_up_client on incrementals")
Signed-off-by: Raphael Zimmer <raphael.zimmer@tu-ilmenau.de>
Reviewed-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.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=05c90e059269f087becfcce23348496085835c29

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

The original Linux kernel CVE announcement for CVE-2026-68158 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68158

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:N/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: 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).