[CVE-2026-68160][IMPORTANT] ceph: fix pre-auth out-of-bounds read on snaptrace in ceph_handle_caps()

[CVE-2026-68160][IMPORTANT] ceph: fix pre-auth out-of-bounds read on snaptrace in ceph_handle_caps()

[AL-KERNEL]

CVE: CVE-2026-68160
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: ceph: fix pre-auth out-of-bounds read on snaptrace in ceph_handle_caps()
Commit: 9081c71796724ffe96cba253f68fbe42363c5295
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9081c71796724ffe96cba253f68fbe42363c5295
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68160
Analysis date: Mon, 10 Aug 2026 14:46:42 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A malicious or compromised Ceph MDS can send a crafted caps message with an oversized snap_trace_len that causes the CephFS client kernel code to read beyond the message buffer during snaptrace decoding, leading to remote DoS and possible limited kernel memory exposure.

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

The original Linux kernel CVE announcement for CVE-2026-68160 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68160

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
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CVE-2026-68160	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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:L/A:H';CWE-125;CWE-130;*CWE-20;Other CVSS 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '8.6';DESCR 'A pre auth out of bounds read exists in the CephFS client capability handling path because ceph_handle_caps reads snap_trace_len from a network supplied ceph_mds_caps header and uses it to construct the snaptrace end pointer before validating that the range is inside the message front buffer. A malicious or compromised MDS can set an oversized snap_trace_len and use a low message version so the version gated decoder blocks do not validate the field before the CEPH_CAP_OP_IMPORT path reaches ceph_update_snap_trace. This can make the kernel decode snap realm data past the legitimate message buffer and may lead to a kernel crash or limited exposure of adjacent kernel memory through decoder side effects. For the CVSS the PR:N is used because the attacker does not need privileges on the victim host and only needs network level ability to act as or influence the MDS endpoint used by the Ceph client. The issue is network reachable for systems that mount CephFS from an attacker controlled or compromised Ceph cluster. Impact is at least remote denial of service and in the paranoid score may include limited confidentiality and integrity impact due to the kernel OOB read primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	OOB DISK IMPROVEONLY LINUS KPANIC 	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: **6**
* Paranoid score: **7**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* **Remote reachable / network-triggerable: +2**
  The malformed `ceph_mds_caps` message is supplied by an MDS endpoint over the CephFS client protocol. Practical triggering requires a malicious or compromised MDS, or equivalent influence over the Ceph client connection.

* **Reliable kernel crash / strong DoS: +1**
  An oversized `snap_trace_len` can make the kernel decoder read beyond the legitimate message front buffer. This can plausibly cause an Oops or kernel crash.

* **Availability impact realistic: +1**
  The affected code runs in kernel CephFS client handling. A crash is host-wide and not limited to a single user process.

* **Confidentiality impact plausible: +1**
  The primitive is an attacker-controlled OOB read in kernel message decoding. Direct disclosure is not demonstrated, but limited adjacent-memory exposure through decoder behavior is technically plausible.

* **Important filesystem/storage path: +1**
  The bug is in CephFS client capability handling, a network filesystem metadata/control path.

Paranoid-only signal:

* **Integrity impact plausible: +1**
  The OOB data can be interpreted as snap realm metadata and influence subsequent decode/state handling. This is not a demonstrated write primitive, so it is only counted in the paranoid score.

Not counted:

* **Generic memory corruption: +0**
  This is an OOB read, not an OOB write, UAF, double-free, arbitrary write, or controlled overwrite.

* **Privilege escalation plausible: +0**
  No concrete LPE primitive is shown.

* **Local unprivileged trigger: +0**
  The primary attacker is the remote MDS side, not a local unprivileged process.

Call-site confidence: **high**. The patch and description show the exact vulnerable call flow from `ceph_handle_caps()` to `ceph_update_snap_trace()`.

## 3. Reachability analysis

The bug is triggerable by a malicious or compromised Ceph MDS that can send crafted capability messages to a CephFS client. The victim does not need to grant local privileges to the attacker, so practical PR is effectively **PR:N** from the victim host perspective, assuming the attacker controls or can influence the MDS endpoint used by the client.

This is not a public Internet exposure in most deployments. CephFS is usually used inside storage or data-center networks. However, within a Ceph deployment the affected path is a normal client protocol path and does not require unusual local kernel configuration once CephFS is mounted.

Namespaces and containers do not materially reduce the remote MDS-side trigger condition. The key prerequisite is that the target host runs a vulnerable CephFS client connected to an attacker-controlled or compromised cluster endpoint.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because it is a network-reachable kernel OOB read in a filesystem client protocol path. The realistic impact is remote DoS via kernel crash.

The paranoid interpretation is higher because the attacker controls the length used to construct decoder bounds, and the decoded OOB data can influence snap realm parsing. Still, there is no demonstrated OOB write, UAF reclaim, arbitrary write, type confusion, or direct privilege escalation primitive. Therefore this should be treated as **Actionable Moderate at minimum**, with a defensible **Strong Important candidate** classification for manual review.

## 5. One-sentence report phrase

A malicious or compromised Ceph MDS can send a crafted caps message with an oversized snap_trace_len that causes the CephFS client kernel code to read beyond the message buffer during snaptrace decoding, leading to remote DoS and possible limited kernel memory exposure.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

This is network reachable in real CephFS deployments and involves an attacker-controlled kernel OOB read before proper bounds validation. Even though LPE is not demonstrated, the combination of remote protocol reachability, kernel memory access, and filesystem metadata parsing warrants manual security review.

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

Patch: ceph: fix pre-auth out-of-bounds read on snaptrace in ceph_handle_caps()
Commit: 9081c71796724ffe96cba253f68fbe42363c5295
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9081c71796724ffe96cba253f68fbe42363c5295

Commit description:

ceph_handle_caps() reads snap_trace_len from the wire-format
ceph_mds_caps header and uses it unconditionally to build a fake
end pointer (snaptrace + snaptrace_len) that is later handed to
ceph_update_snap_trace() in the CEPH_CAP_OP_IMPORT case:

    snaptrace     = h + 1;
    snaptrace_len = le32_to_cpu(h->snap_trace_len);
    p             = snaptrace + snaptrace_len;
    ...
    case CEPH_CAP_OP_IMPORT:
        if (snaptrace_len) {
            ...
            if (ceph_update_snap_trace(mdsc, snaptrace,
                                       snaptrace + snaptrace_len,
                                       false, &realm)) { ... }

ceph_update_snap_trace() then decodes a struct ceph_mds_snap_realm
from snaptrace using ceph_decode_need(&p, e, sizeof(*ri), bad)
with the attacker-supplied fake end e == snaptrace + snaptrace_len.
With snaptrace_len == 0xFFFFFFFF the bound check is trivially
satisfied, ri = p reads sizeof(struct ceph_mds_snap_realm) past
the legitimate msg->front buffer, and ri->num_snaps /
ri->num_prior_parent_snaps then drive further out-of-bounds
reads of the encoded snap arrays.

The eleven msg_version >= 2 .. msg_version >= 12 decoder blocks
above the op switch each catch this OOB through their
ceph_decode_*_safe() / ceph_decode_need() helpers, but they sit
behind a hdr.version-gated if, so a malicious or compromised
MDS that sets msg->hdr.version = 1 reaches the IMPORT path with
no version-gated decoder having validated snap_trace_len. The
shape has been present since ceph_handle_caps() was introduced.

Validate snap_trace_len against the message front buffer before
consuming it, using the canonical ceph_decode_need() / ceph_has_room()
helper.  The helper bounds the length with subtraction (n <= end - p,
guarded by end >= p) rather than pointer addition, so it is wrap-safe
for the attacker-controlled u32 length on 32-bit builds where
p + snap_trace_len could overflow the address space.  This matches the
rest of the ceph decode path (e.g. the pool_ns_len check a few lines
below), and the existing goto bad cleanup already covers this exit
path.

Cc: stable@vger.kernel.org
Fixes: a8599bd ("ceph: capability management")
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Reviewed-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/ceph/caps.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=9081c71796724ffe96cba253f68fbe42363c5295

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

The original Linux kernel CVE announcement for CVE-2026-68160 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68160

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:L/A:H
  The Best / paranoid CVSS score: 8.6

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: 6
  Paranoid ActionableScore: 7

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).