[CVE-2026-46119][MODERATE 7.0] libceph: Fix slab-out-of-bounds access in auth message processing

[CVE-2026-46119][MODERATE 7.0] libceph: Fix slab-out-of-bounds access in auth message processing

[AL-KERNEL]

CVE: CVE-2026-46119
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: libceph: Fix slab-out-of-bounds access in auth message processing
Commit: 2ae0afd98432536562fa8261538ae795446f0589
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2ae0afd98432536562fa8261538ae795446f0589
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46119
Analysis date: Thu, 28 May 2026 14:19:29 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A malicious Ceph monitor can send a positive auth result that libceph reuses as an auth request front length, causing a slab out-of-bounds read and leaking kernel memory back to the peer.

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

The original Linux kernel CVE announcement for CVE-2026-46119 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46119

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-2026-46119	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:H/I:N/A:H';CWE-125;*CWE-200;*CWE-20;Other CVSS 'AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L';BEST CVSS score: '9.1';DESCR 'A malicious or compromised Ceph monitor can return a positive auth result value that libceph incorrectly treats as an error code and later reuses as the front segment length for a preallocated CEPH_MSG_AUTH request. This can make the client send bytes beyond the allocated auth front buffer, causing a slab out-of-bounds read and leaking guest or host kernel memory back to the peer. For the CVSS the PR:N is used because the attacker needs only network position as the Ceph monitor endpoint or equivalent traffic control, not a local account on the victim. The issue is network reachable in the Ceph client to monitor authentication path, but exposure is usually limited to Ceph storage networks rather than the public Internet. Impact is primarily high confidentiality loss. Availability can also be affected if the OOB read faults or triggers hardened kernel diagnostics, while no integrity or privilege escalation primitive is shown.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 6) 	MAYBE	REMOTE OOB SIMPLEFIX NETWORK LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	-	-	checked

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

ActionableScore=6
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: **5**
* Paranoid score: **6**
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

* Remote reachable / network-triggerable: **+2**. A malicious or compromised Ceph monitor, or an attacker with equivalent monitor traffic control, can send the crafted `CEPH_MSG_AUTH_REPLY`.
* Confidentiality impact plausible: **+1**. The commit explicitly states that memory beyond the allocated auth front buffer can be sent out.
* Practical exploit chain strongly implied: **+1**. The described chain is concrete: positive auth result value -> reused as front segment length -> OOB read -> data sent to peer.
* Important filesystem/storage path: **+1**. Ceph is a storage/filesystem client path, and authentication to monitors is security-sensitive.
* Availability impact realistic, paranoid: **+1**. The OOB read may fault or trigger hardened/debug checks, especially with the added `BUG_ON()` indicating this state is invalid.
* No write primitive: **+0**. The patch shows slab OOB read and disclosure, not OOB write, UAF, arbitrary write, or direct privilege escalation.
* No integrity signal: **+0**. There is no demonstrated modification of kernel state or attacker-controlled write.

## 3. Reachability analysis

The attacker needs to influence the Ceph monitor authentication reply. This is realistic for a malicious, compromised, or spoofed Ceph monitor endpoint, or for an attacker with MITM capability on the Ceph monitor path. No local account on the victim is required. The issue is network reachable in the Ceph client-to-monitor authentication path, but practical exposure is usually limited to Ceph storage networks rather than the public Internet. Containers are not central unless they control Ceph client configuration or can make the host connect to an attacker-controlled monitor.

## 4. Severity interpretation

This behaves like an **Actionable Moderate**, close to an Important candidate in environments where Ceph monitor traffic is exposed to untrusted actors. The realistic demonstrated impact is high-confidence kernel memory disclosure to the peer. It is not a proven LPE or RCE issue because the primitive is read-only and no write or control-flow corruption is shown. However, network-triggered kernel memory disclosure from a storage authentication path should not be auto-closed.

## 5. One-sentence report phrase

A malicious Ceph monitor can send a positive auth result that libceph reuses as an auth request front length, causing a slab out-of-bounds read and leaking kernel memory back to the peer.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Manual review is required because this is a network-reachable kernel memory disclosure in Ceph authentication handling, with an explicit OOB read and data exfiltration path.

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

Patch: libceph: Fix slab-out-of-bounds access in auth message processing
Commit: 2ae0afd98432536562fa8261538ae795446f0589
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2ae0afd98432536562fa8261538ae795446f0589

Commit description:

If a (potentially corrupted) message of type CEPH_MSG_AUTH_REPLY
contains a positive value in its result field, it is treated as an
error code by ceph_handle_auth_reply() and returned to
handle_auth_reply(). Thereafter, an attempt is made to send the
preallocated message of type CEPH_MSG_AUTH, where the returned value is
interpreted as the size of the front segment to send. If the result
value in the message is greater than the size of the memory buffer
allocated for the front segment, an out-of-bounds access occurs, and
the content of the memory region beyond this buffer is sent out.

This patch fixes the issue by treating only negative values in the
result field as errors. Positive values are therefore treated as success
in the same way as a zero value. Additionally, a BUG_ON is added to
__send_prepared_auth_request() comparing the len parameter to
front_alloc_len to prevent sending the message if it exceeds the bounds
of the allocation and to make it easier to catch any logic flaws leading
to this.

Cc: stable@vger.kernel.org
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/auth.c
  net/ceph/mon_client.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=2ae0afd98432536562fa8261538ae795446f0589

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

The original Linux kernel CVE announcement for CVE-2026-46119 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46119

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:H/I:N/A:L
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
  The Best / paranoid CVSS score: 9.1

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: 5
  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).