[CVE-2026-68433][MODERATE REGULAR] libceph: bound get_version reply decode to front len

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

CVE: CVE-2026-68433
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: libceph: bound get_version reply decode to front len
Commit: 340e0386aa39da181015bee38f309018c335ce16
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=340e0386aa39da181015bee38f309018c335ce16
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68433
Analysis date: Tue, 11 Aug 2026 20:51:46 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A truncated Ceph MON_GET_VERSION_REPLY can make libceph decode stale bytes from a reused front buffer because the handler used the allocated buffer length instead of the received length, creating a network-reachable stale-read condition with limited confidentiality and integrity concern.

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

The original Linux kernel CVE announcement for CVE-2026-68433 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68433

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
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CVE-2026-68433	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	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:L';CWE-125;*CWE-457;*CWE-20;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N';BEST CVSS score: '5.6';DESCR 'libceph handle_get_version_reply used msg front_alloc_len as the decode boundary for MON_GET_VERSION_REPLY instead of msg front iov_len, so a truncated monitor reply could pass length checks and decode stale bytes left in the reused front buffer. This is an invalid read of data that was not received from the wire, with possible low confidentiality impact if stale buffer content influences an observable version result and possible low integrity impact if the client acts on a corrupted version value. For the CVSS the PR:N value is used because the attacker does not need local privileges on the victim, but practical triggering usually requires a malicious or compromised Ceph monitor endpoint or the ability to tamper with monitor traffic. The issue is network reachable over the Ceph monitor connection, but Ceph monitor networks are normally internal storage networks rather than public Internet services. Impact is not a direct kernel crash or privilege escalation based on the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 4)	YES	REMOTE READ SIMPLEFIX NETWORK LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	guess

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

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

## 2. Signal breakdown

Triggered signals:

* Remote reachable / network-triggerable: +2
  The malformed MON_GET_VERSION_REPLY is received over the Ceph monitor connection. Practical triggering likely requires a malicious or compromised monitor, or MITM capability on Ceph monitor traffic.

* Confidentiality impact plausible: +1
  The bug can decode stale bytes from a reused kernel message buffer. This is an uninitialized or stale read, but no direct user-visible leak primitive is demonstrated.

* Integrity impact plausible: +1
  A corrupted decoded version value could influence client-side logic for the get_version reply, but this is limited and not equivalent to arbitrary state corruption.

Paranoid-only signal:

* Availability impact plausible: +1
  A malformed reply could plausibly cause request failure or client misbehavior, but the patch does not show a reliable kernel crash.

Negative / limiting signals:

* Rare or deployment-limited exposure: -1
  Ceph monitor traffic is normally on internal storage networks and requires a configured Ceph client environment.

Not awarded:

* No generic memory corruption bonus. This is an invalid stale-buffer read, not UAF, OOB write, double free, type confusion, or arbitrary write.
* No privilege escalation bonus. No reclaim, overwrite, callback control, refcount abuse, or LPE primitive is shown.
* No strong DoS bonus. The patch does not describe panic, Oops, or reliable crash.

Call-site confidence: medium. The affected handler and decode boundary are visible, but broader user-visible consequences of the decoded version value are not shown in the patch.

## 3. Reachability analysis

The bug can be triggered by a truncated Ceph monitor reply to a Linux Ceph client. In CVSS terms the attacker needs no local privileges on the victim, but practical exploitation usually requires control of a Ceph monitor endpoint or ability to tamper with monitor traffic. Namespaces and containers do not materially lower the privilege requirement unless they can influence the victim host Ceph client connection. The path is not generally Internet-facing and is only relevant on systems using libceph/Ceph client functionality.

## 4. Severity interpretation

This behaves more like an actionable Moderate / borderline manual-review issue than an Important-class kernel vulnerability. The theoretical concern is stale kernel-buffer data being decoded from a network reply, which supports low confidentiality and integrity concern. Realistic exploitation evidence is weaker: there is no demonstrated crash, no write primitive, no UAF, and no privilege escalation path.

## 5. One-sentence report phrase

A truncated Ceph MON_GET_VERSION_REPLY can make libceph decode stale bytes from a reused front buffer because the handler used the allocated buffer length instead of the received length, creating a network-reachable stale-read condition with limited confidentiality and integrity concern.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the issue is network-reachable in Ceph deployments and involves stale kernel-buffer reads, but the patch does not support strong memory corruption, reliable DoS, or privilege escalation.

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

Patch: libceph: bound get_version reply decode to front len
Commit: 340e0386aa39da181015bee38f309018c335ce16
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=340e0386aa39da181015bee38f309018c335ce16

Commit description:

handle_get_version_reply() uses msg->front_alloc_len as the decode
boundary for MON_GET_VERSION_REPLY.  That is the size of the reused
reply buffer, not the number of bytes actually received.

A truncated reply can therefore pass ceph_decode_need() and decode the
second u64 from stale tail bytes left in the buffer by an earlier
message, causing an uninitialized memory read.

Use msg->front.iov_len as the receive-side decode boundary, matching
other libceph reply handlers and limiting decoding to the bytes that
were actually read from the wire.

Cc: stable@vger.kernel.org
Fixes: 513a824 ("libceph: mon_get_version request infrastructure")
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Zhengchuan Liang <zcliangcn@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Assisted-by: Codex:GPT-5.4
Signed-off-by: Douya Le <ldy3087146292@gmail.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Reviewed-by: Viacheslav Dubeyko <slava@dubeyko.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  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=340e0386aa39da181015bee38f309018c335ce16

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

The original Linux kernel CVE announcement for CVE-2026-68433 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68433

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:L/I:L/A:N
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L
  The Best / paranoid CVSS score: 5.6

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: 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).