[CVE-2026-52956][MODERATE 7.0] libceph: Fix potential out-of-bounds access in __ceph_x_decrypt()

[CVE-2026-52956][MODERATE 7.0] libceph: Fix potential out-of-bounds access in __ceph_x_decrypt()

[AL-KERNEL]

CVE: CVE-2026-52956
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: libceph: Fix potential out-of-bounds access in __ceph_x_decrypt()
Commit: c7e9b53aebe401970f1b5f5a01b4e021b18e8bb2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c7e9b53aebe401970f1b5f5a01b4e021b18e8bb2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52956
Analysis date: Wed, 24 Jun 2026 14:42:50 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A network-reachable out-of-bounds read in libceph CephX authentication can be triggered by a malicious or compromised monitor returning a too-short encrypted auth payload, causing at least kernel DoS and limited worst-case confidentiality concern.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-52956 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52956

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-2026-52956	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:N/A:H';CWE-125;CWE-126;*CWE-20;Other CVSS 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '8.2';DESCR 'An out-of-bounds read in the CephX decrypt path can occur because __ceph_x_decrypt() reads hdr magic from a decrypted buffer before verifying that the plaintext is large enough to contain a ceph_x_encrypt_header. A malicious or compromised Ceph monitor endpoint can trigger this by returning a short authentication payload such as a short FRAME_TAG_AUTH_REPLY_MORE ciphertext. For the CVSS the PR:N is used because no privileges are required on the victim host beyond network reachability to the Ceph authentication peer. The issue is network reachable in deployments where an attacker can act as the Ceph monitor or tamper with monitor traffic. Impact is at least denial of service via kernel crash. The paranoid score keeps limited confidentiality impact because the primitive is an invalid kernel read, but no arbitrary write or direct privilege escalation primitive is shown.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE WRITE OOB 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

Conservative signals:

* Remote reachable / network-triggerable: +2
  The affected CephX authentication path processes data received from a Ceph monitor or authentication peer over the network.
* Reliable kernel crash / strong DoS: +1
  A short encrypted authentication payload can cause an out-of-bounds read of `hdr->magic` in kernel code, which can plausibly lead to an Oops, KASAN report, or kernel crash.
* Important filesystem/storage path: +1
  This is in libceph authentication code used by Ceph-backed storage and filesystem clients.
* Rare AND difficult-to-reach subsystem/configuration: -1
  The path is relevant only on systems using Ceph/libceph authentication and reachable monitor traffic, not on a default generic Linux host.

Paranoid additional signal:

* Confidentiality impact plausible: +1
  The primitive is an invalid kernel read in a network authentication path. No direct disclosure primitive is shown, but limited confidentiality concern is defensible for manual-review sensitivity.

Not applied:

* Privilege escalation plausible: +0
  No write primitive, reclaim primitive, type confusion, callback corruption, or refcount takeover is shown.
* Generic memory corruption strong primitive: +0
  This is an out-of-bounds read, not an OOB write, UAF, double free, or arbitrary write.
* Integrity impact plausible: +0
  The patch only prevents a too-short plaintext from being interpreted as a header. No modification of protected data is indicated.

## 3. Reachability analysis

A malicious or compromised Ceph monitor, or an attacker able to tamper with Ceph monitor authentication traffic, can provide a short authentication response such as a short `FRAME_TAG_AUTH_REPLY_MORE` ciphertext. The victim does not need to run local attacker code, so the practical CVSS PR interpretation is PR:N when the Ceph authentication peer is reachable or attacker-controlled.

This is not Internet-default exposure for most systems. Ceph deployments are usually internal storage or data-center networks. However, for hosts using Ceph clients, the vulnerable parser is reached through normal network authentication traffic, so the issue should not be treated like a purely local cleanup bug.

Namespaces and containers do not materially reduce the attacker requirement unless they control Ceph client configuration or monitor reachability. The realistic attacker model is network-positioned, malicious monitor, compromised monitor, or MITM of monitor traffic.

## 4. Severity interpretation

This behaves like an actionable Moderate issue, with Important-class review sensitivity due to network reachability and kernel OOB access. The realistic demonstrated impact is DoS through an out-of-bounds read and possible kernel crash.

The theoretical worst case includes limited confidentiality concern because kernel memory is read out of bounds, but the patch does not show a direct disclosure channel, attacker-controlled write, privilege escalation primitive, or memory lifetime corruption. Therefore the conservative score remains below Important, while the paranoid score reaches the actionable threshold.

## 5. One-sentence report phrase

A network-reachable out-of-bounds read in libceph CephX authentication can be triggered by a malicious or compromised monitor returning a too-short encrypted auth payload, causing at least kernel DoS and limited worst-case confidentiality concern.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This is network-reachable kernel OOB access in an authentication path. The currently supported impact is mainly DoS, but the parser location and invalid kernel read justify manual review rather than auto-closure.

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

Patch: libceph: Fix potential out-of-bounds access in __ceph_x_decrypt()
Commit: c7e9b53aebe401970f1b5f5a01b4e021b18e8bb2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c7e9b53aebe401970f1b5f5a01b4e021b18e8bb2

Commit description:

In __ceph_x_decrypt(), a part of the buffer p is interpreted as a
ceph_x_encrypt_header, and the magic field of this struct is accessed.
This happens without any guarantee that the buffer is large enough to
hold this struct. The function parameter ciphertext_len represents the
length of the ciphertext to decrypt and is guaranteed to be at most the
remaining size of the allocated buffer p. However, this value is not
necessarily greater than sizeof(ceph_x_encrypt_header). E.g., a message
frame of type FRAME_TAG_AUTH_REPLY_MORE, that is just as long to hold
the ciphertext at its end with a ciphertext_len of 8 or less, can
trigger an out-of-bounds memory access when accessing hdr->magic.

This patch fixes the issue by adding a check to ensure that the
decrypted plaintext in the buffer is large enough to represent at least
the ceph_x_encrypt_header.

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_x.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=c7e9b53aebe401970f1b5f5a01b4e021b18e8bb2

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

The original Linux kernel CVE announcement for CVE-2026-52956 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52956

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:N/A:H
  The Best / paranoid CVSS score: 8.2

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).