[CVE-2026-52958][MODERATE 7.0] libceph: Fix potential out-of-bounds access in osdmap_decode()

[CVE-2026-52958][MODERATE 7.0] libceph: Fix potential out-of-bounds access in osdmap_decode()

[AL-KERNEL]

CVE: CVE-2026-52958
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: libceph: Fix potential out-of-bounds access in osdmap_decode()
Commit: 36a79759a288961b1ff28a68ec2d1f56f6848098
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=36a79759a288961b1ff28a68ec2d1f56f6848098
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52958
Analysis date: Thu, 25 Jun 2026 03:53:14 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A malformed Ceph osdmap can cause libceph osdmap_decode() to read past the received buffer because the size check accounts for only one osd_weight entry instead of map max_osd entries, making this a network-fed kernel OOB read with practical DoS impact and limited worst-case C/I concern.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-52958 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52958

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-2026-52958	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';CWE-125;*CWE-20;CWE-130;Other CVSS 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '8.6';DESCR 'An out of bounds read in libceph osdmap_decode() can occur because the ceph_decode_need() size check accounts for osd_weight only once while the decoder later reads osd_state and osd_weight for map max_osd entries. A corrupted or malicious osdmap with max_osd larger than the remaining message content can make the kernel decoder read past the end of the received buffer. For the CVSS the PR:N is used because a malicious or compromised Ceph monitor or network attacker able to tamper with Ceph traffic can deliver the malformed osdmap without local privileges on the victim. The issue is network reachable in Ceph client deployments that accept osdmap updates from the affected peer path, although Ceph storage networks are usually internal and trusted rather than public Internet exposed. Impact is at least denial of service via kernel crash. For the paranoid score, limited confidentiality or integrity impact is kept possible because the primitive is an out of bounds read in kernel memory, but there is no clear arbitrary write primitive in the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4) 	MAYBE	REMOTE WRITE OOB DANGER SIMPLEFIX NETWORK LINUS  DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2
  Malformed osdmap data is received over the Ceph protocol path. A malicious or compromised Ceph monitor, or an attacker able to tamper with Ceph traffic, can influence the input.
* Reliable kernel crash / strong DoS: +1
  The bounds check is too small and decoding can read beyond the received osdmap buffer, plausibly causing a kernel fault.
* Weak corruption / limited OOB read: +0
  The primitive is an out-of-bounds read, not an OOB write, UAF, double free, or arbitrary write.
* Rare / deployment-specific subsystem: -1
  Ceph client deployments are common in storage environments but not enabled by default on typical Linux systems.

Paranoid additional signals:

* Confidentiality impact plausible: +1
  The bug is an OOB read in kernel context. No direct disclosure path is shown, but manual review is justified to confirm whether adjacent decoded data can become visible or influence later behavior.
* Integrity impact plausible: +1
  Limited integrity concern is defensible because malformed decoded state could affect osdmap interpretation, although there is no demonstrated arbitrary write or strong corruption primitive.
* Important storage path: +1
  libceph is a kernel storage client path, and malformed cluster metadata can affect storage availability and client behavior.

## 3. Reachability analysis

The likely trigger is a corrupted or malicious osdmap delivered to a Linux Ceph client. No local privileges are required on the victim if the attacker controls or compromises a Ceph monitor, or can tamper with Ceph storage network traffic. This is not usually public Internet exposed, because Ceph is normally deployed on internal storage or data-center networks. Containers and namespaces do not significantly lower the trigger requirement unless they can configure or access the host Ceph client path. The realistic condition is access to the Ceph trust boundary, not ordinary unauthenticated Internet access.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because it is a network-fed kernel parser bug in a storage subsystem. The demonstrated primitive is still limited: an out-of-bounds read during decode, with no supported arbitrary write, UAF reclaim, or privilege escalation chain. Realistically it behaves mainly as remote or adjacent-network DoS against Ceph clients. Paranoid scoring raises it to Actionable Moderate because kernel OOB reads from network-controlled metadata can be underestimated and should not be auto-closed without manual review.

## 5. One-sentence report phrase

A malformed Ceph osdmap can cause libceph osdmap_decode() to read past the received buffer because the size check accounts for only one osd_weight entry instead of map max_osd entries, making this a network-fed kernel OOB read with practical DoS impact and limited worst-case C/I concern.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: network-reachable kernel out-of-bounds read in libceph storage metadata parsing. The obvious impact is DoS, but the OOB read and metadata decode context justify manual confirmation of any confidentiality or integrity side effects.

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

Patch: libceph: Fix potential out-of-bounds access in osdmap_decode()
Commit: 36a79759a288961b1ff28a68ec2d1f56f6848098
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=36a79759a288961b1ff28a68ec2d1f56f6848098

Commit description:

When decoding osd_state and osd_weight from an incoming osdmap in
osdmap_decode(), both are decoded for each osd, i.e., map->max_osd
times. The ceph_decode_need() check only accounts for
sizeof(*map->osd_weight) once. This can potentially result in an
out-of-bounds memory access if the incoming message is corrupted such
that the max_osd value exceeds the actual content of the osdmap message.

This patch fixes the issue by changing the corresponding part in the
ceph_decode_need() check to account for
map->max_osd*sizeof(*map->osd_weight).

Cc: stable@vger.kernel.org
Fixes: dcbc919 ("libceph: switch osdmap decoding to use ceph_decode_entity_addr")
Signed-off-by: Raphael Zimmer <raphael.zimmer@tu-ilmenau.de>
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=36a79759a288961b1ff28a68ec2d1f56f6848098

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

The original Linux kernel CVE announcement for CVE-2026-52958 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52958

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:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 8.6

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: 3
  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: NO
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).