[CVE-2026-43304][IMPORTANT] libceph: define and enforce CEPH_MAX_KEY_LEN [ Upstream

[CVE-2026-43304][IMPORTANT] libceph: define and enforce CEPH_MAX_KEY_LEN [ Upstream

[AL-KERNEL]

CVE: CVE-2026-43304
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: libceph: define and enforce CEPH_MAX_KEY_LEN [ Upstream
Commit: 6405e8c680974bb74e2c98d5249fb52c7b12a6c6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6405e8c680974bb74e2c98d5249fb52c7b12a6c6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43304
Analysis date: Wed, 20 May 2026 19:59:14 -0400
ActionableScore: 8
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate
Manual review required: YES

Summary:
An oversized Ceph authentication key from an attacker-controlled or compromised monitor endpoint can reach fixed libceph messenger v2 auth buffers, creating a kernel memory corruption and crash risk during authentication.

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

The original Linux kernel CVE announcement for CVE-2026-43304 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43304

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: IMPORTANT
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-2026-43304	IMPORTANT	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-121;*CWE-20;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.1';DESCR 'libceph accepted key material length from a Ceph authentication reply without enforcing that it fits the fixed session key buffer used by messenger v2 auth completion. A malicious or compromised Ceph monitor endpoint, or an attacker able to tamper with monitor traffic, could provide an oversized key and potentially corrupt kernel memory during auth processing. For the CVSS the PR:N is used because the attacker does not need credentials on the victim if they control or can impersonate the Ceph auth endpoint. The issue is network reachable only in the Ceph monitor/auth path and requires that the client talks to an attacker influenced endpoint, so AC:H is used. Impact is at least denial of service via kernel crash, and worst case may allow confidentiality or integrity impact because the primitive is an oversized network supplied key reaching fixed kernel auth buffers. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 7)	YES	REMOTE NETWORK LINUS KPANIC 	NO	NO	checked

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

ActionableScore=8
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate**::

## 2. Signal breakdown

Conservative score signals:

* Firmware or endpoint mediated external influence: +1. The malicious input comes from the Ceph authentication peer, typically a monitor or an attacker able to tamper with that traffic.
* Generic memory corruption, strong primitive: +2. The commit explicitly adds a maximum key length because decoded key material must fit a fixed size buffer in `process_auth_done()`.
* Reliable kernel crash / strong DoS: +1. Oversized authentication material reaching fixed kernel buffers can plausibly crash the kernel.
* Availability impact realistic: +1. A kernel crash in the Ceph client auth path is a system-wide DoS.
* Integrity impact plausible: +1. Oversized attacker-influenced key material reaching a fixed buffer is a plausible corruption sink.
* Rare/configuration-dependent exposure: -1. This only affects systems using kernel Ceph/libceph clients and messenger v2 authentication with attacker-influenced monitor/auth replies.

Paranoid additions:

* Remote reachable / network-triggerable interpretation: +1 over conservative. If the attacker controls or impersonates the Ceph monitor/auth endpoint, the trigger is network-delivered and does not require local access on the victim.
* Weak privilege-escalation or kernel compromise concern: +1. Fixed-buffer corruption during network authentication is security-sensitive, although no arbitrary write or reliable exploitation primitive is shown.
* Confidentiality impact plausible: +1. In worst case, kernel memory corruption during auth processing may create disclosure or broader compromise paths.

## 3. Reachability analysis

The attacker is not an arbitrary Internet packet sender in the usual case. They need to control a Ceph monitor/auth endpoint, compromise it, impersonate it, or tamper with Ceph monitor traffic. No local user account on the victim is required in that model. Containers do not materially change the trigger unless they can cause the host kernel Ceph client to connect to attacker-controlled Ceph infrastructure. The path is not default-enabled on all Linux systems, but it is realistic on hosts using CephFS/RBD or other kernel Ceph clients.

## 4. Severity interpretation

Conservatively this is an Actionable Moderate because exposure is Ceph-specific and requires attacker influence over the auth peer. Paranoid triage reaches Strong Important candidate because the patch prevents oversized network-supplied key material from reaching fixed kernel authentication buffers, which is a concrete memory corruption pattern. Practical exploitation beyond DoS is not demonstrated, but the bug should not be auto-closed.

## 5. One-sentence report phrase

An oversized Ceph authentication key from an attacker-controlled or compromised monitor endpoint can reach fixed libceph messenger v2 auth buffers, creating a kernel memory corruption and crash risk during authentication.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: this is network-influenced fixed-buffer memory corruption in kernel Ceph authentication. Exposure is deployment-specific, but the primitive is strong enough to require manual review.

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

Patch: libceph: define and enforce CEPH_MAX_KEY_LEN [ Upstream
Commit: 6405e8c680974bb74e2c98d5249fb52c7b12a6c6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6405e8c680974bb74e2c98d5249fb52c7b12a6c6

Changed files:
  net/ceph/crypto.c
  net/ceph/crypto.h
  net/ceph/messenger_v2.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=6405e8c680974bb74e2c98d5249fb52c7b12a6c6

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

The original Linux kernel CVE announcement for CVE-2026-43304 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43304

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:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 8.1

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: 6
  Paranoid ActionableScore: 8

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).