[CVE-2026-46024][MODERATE REGULAR] libceph: Prevent potential null-ptr-deref in ceph_handle_auth_reply()

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

CVE: CVE-2026-46024
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: libceph: Prevent potential null-ptr-deref in ceph_handle_auth_reply()
Commit: 4b2738b93edad661178340239de657d876b73d3d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4b2738b93edad661178340239de657d876b73d3d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46024
Analysis date: Wed, 27 May 2026 10:45:34 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A crafted Ceph auth reply with protocol 0 can leave `ac->ops` NULL and trigger a kernel NULL pointer dereference during authentication, mainly allowing DoS from a malicious or intercepted monitor path.

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

The original Linux kernel CVE announcement for CVE-2026-46024 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46024

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
======================================================================

CVE-2026-46024	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:N/I:N/A:H';**CWE-476;*CWE-20;CWE-703;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'A NULL pointer dereference can occur in libceph auth handling when a CEPH_MSG_AUTH_REPLY carries protocol 0 and result 0 during negotiation. This can reset ac protocol to 0 and ac ops to NULL, skip protocol initialization, and later call ac ops handle_reply through a NULL pointer. For the CVSS the PR:N is used in the paranoid score because a malicious or compromised Ceph monitor endpoint, or an attacker able to tamper with monitor traffic, can provide the crafted auth reply without local privileges on the victim. The issue is network reachable only in deployments where the Ceph client connects to an attacker controlled or intercepted monitor path. Impact is denial of service via kernel crash only. The patch context does not support UAF, out of bounds write, arbitrary write, information disclosure, or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 4)	YES	REMOTE NULLPTR SIMPLEFIX NETWORK LINUS  INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Remote/network-influenced trigger: +2
  A crafted `CEPH_MSG_AUTH_REPLY` can be supplied by a malicious or compromised Ceph monitor, or by an attacker able to tamper with monitor traffic.

* Reliable kernel crash / strong DoS: +1
  The bad state leads to `ac->ops == NULL` followed by `ac->ops->handle_reply()`, causing NULL pointer dereference.

* Availability impact realistic: +1
  Successful triggering can crash the kernel or at least the Ceph client kernel path.

Subtracting signals:

* Deployment and trust-path dependent: -1
  The attacker generally must control or intercept the Ceph monitor/auth reply path. This is not arbitrary Internet packet exposure.

Paranoid additional consideration:

* Storage/network service exposure concern: +1
  In Ceph deployments, monitor traffic is a critical network dependency. A compromised monitor endpoint can affect multiple clients, so this should not be auto-closed as a trivial local-only NULL dereference.

No signals apply for UAF, OOB write, arbitrary write, page-cache corruption, privilege escalation, or direct confidentiality/integrity impact.

## 3. Reachability analysis

The bug is reachable during Ceph authentication negotiation when a `CEPH_MSG_AUTH_REPLY` contains `protocol = 0` and `result = 0`. A normal local user is not the expected trigger. The realistic attacker is a malicious Ceph monitor, a compromised monitor, or a network attacker capable of modifying monitor traffic.

Namespaces and containers are not central unless they control Ceph client configuration or monitor reachability. The path is not broadly exposed like TCP/IP core packet parsing, but it is network-influenced in systems using kernel Ceph clients.

## 4. Severity interpretation

This behaves like a network-influenced DoS issue, not an Important memory-corruption issue. The primitive is a NULL pointer dereference caused by invalid auth protocol state, not UAF, heap corruption, OOB access, or arbitrary write.

The realistic impact is kernel crash or Ceph client disruption. The theoretical risk does not extend to privilege escalation based on the patch alone.

## 5. One-sentence report phrase

A crafted Ceph auth reply with protocol 0 can leave `ac->ops` NULL and trigger a kernel NULL pointer dereference during authentication, mainly allowing DoS from a malicious or intercepted monitor path.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is network-influenced and affects a storage authentication path, but the supported primitive is NULL dereference DoS only with no evidence of memory corruption or privilege escalation.

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

Patch: libceph: Prevent potential null-ptr-deref in ceph_handle_auth_reply()
Commit: 4b2738b93edad661178340239de657d876b73d3d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4b2738b93edad661178340239de657d876b73d3d

Commit description:

If a message of type CEPH_MSG_AUTH_REPLY contains a zero value for both
protocol and result, this is currently not treated as an error. In case
of ac->negotiating == true and ac->protocol > 0, this leads to setting
ac->protocol = 0 and ac->ops = NULL. Thereafter, the check for
ac->protocol != protocol returns false, and init_protocol() is not
called. Subsequently, ac->ops->handle_reply() is called, which leads to
a null pointer dereference, because ac->ops is still NULL.

This patch changes the check for ac->protocol != protocol to
!ac->protocol, as this also includes the case when the protocol was set
to zero in the message. This causes the message to be treated as
containing a bad auth protocol.

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

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=4b2738b93edad661178340239de657d876b73d3d

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

The original Linux kernel CVE announcement for CVE-2026-46024 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46024

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:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 7.5

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: 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).