[CVE-2026-68131][MODERATE 7.0] rbd: Reset positive result codes to zero in object map update path

[CVE-2026-68131][MODERATE 7.0] rbd: Reset positive result codes to zero in object map update path

[AL-KERNEL]

CVE: CVE-2026-68131
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: rbd: Reset positive result codes to zero in object map update path
Commit: 14995c4250f04b58bf6fc00e0e973a2e1b3cfb9b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=14995c4250f04b58bf6fc00e0e973a2e1b3cfb9b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68131
Analysis date: Mon, 10 Aug 2026 10:24:28 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A corrupted or malicious Ceph OSD reply can pass a positive result code through the RBD object map update path and trigger a kernel assertion in `__rbd_obj_handle_request()`, causing a network-adjacent denial of service on affected RBD clients.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-68131 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68131

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-2026-68131	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-755;CWE-617;*CWE-20;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.5';DESCR 'An RBD object map update can receive a corrupted positive result code for a write style reply, even though writes must not return a data payload. In the affected path this positive result can be passed through rbd_object_map_callback into __rbd_obj_handle_request and can trigger rbd_assert, causing a kernel crash. For the CVSS the PR:N is used because the attacker does not need a local account on the victim system when acting as a malicious or compromised Ceph OSD endpoint. The issue is network adjacent rather than broadly Internet reachable because RBD and Ceph storage traffic is typically deployed on isolated storage or data center networks. Impact is denial of service only based on the visible primitive, with no supported evidence for information disclosure, integrity corruption, or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	WRITE OOB DANGER 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. A corrupted or malicious Ceph OSD reply can reach the RBD client over the storage network.
* Reliable kernel crash / strong DoS: +1. The positive result code can trigger `rbd_assert(*result < 0)` and crash the kernel.
* Important filesystem/storage path: +1. RBD is a block storage path and failures affect mounted or attached storage clients.

Conservative total: 4

Paranoid additional signal:

* Availability impact realistic: +1. If an attacker controls or compromises an OSD endpoint, the crash condition appears repeatable and host-wide for affected RBD clients.

Paranoid total: 5

Not counted:

* No generic memory corruption. The patch shows assertion-triggered crash, not UAF, OOB write, double free, type confusion, or arbitrary write.
* No privilege escalation plausible. No concrete corruption primitive is visible.
* No confidentiality or integrity impact. The visible impact is DoS only.
* No admin/root penalty. The attacker model is a malicious or compromised Ceph-side endpoint, not a local admin on the victim.

## 3. Reachability analysis

The bug can be triggered by a corrupted, malicious, or compromised Ceph OSD reply to an RBD object map update. The attacker does not need a local account on the victim host if they can influence the storage endpoint or storage-network traffic.

This is not broadly Internet reachable in typical deployments. RBD and Ceph traffic is usually confined to storage or data-center networks. However, it is still network-adjacent and externally influenced from the victim kernel perspective.

Namespaces and containers do not materially lower the trigger requirement unless a containerized workload can configure or route RBD traffic to an attacker-controlled Ceph endpoint. The affected path is only relevant on systems using RBD with object-map or fast-diff related functionality.

Call-site confidence: high. The commit message describes the exact path from `rbd_object_map_callback()` to `__rbd_obj_handle_request()` and the assertion condition.

## 4. Severity interpretation

This behaves like an actionable network-adjacent storage DoS, not like an Important memory-corruption issue. The practical impact is a kernel crash caused by malformed storage protocol state.

Theoretical escalation is not supported by the patch. There is no evidence of attacker-controlled memory reuse, stale pointer use, write-after-free, refcount takeover, object confusion, or page-cache corruption.

Because the trigger is storage-network reachable and affects a kernel block storage client, it should not be treated as an ordinary low-priority Moderate issue.

## 5. One-sentence report phrase

A corrupted or malicious Ceph OSD reply can pass a positive result code through the RBD object map update path and trigger a kernel assertion in `__rbd_obj_handle_request()`, causing a network-adjacent denial of service on affected RBD clients.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Manual review is required because the issue is network-adjacent through Ceph storage traffic and causes a reliable kernel crash, even though the patch does not support memory corruption, information disclosure, or privilege escalation.

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

Patch: rbd: Reset positive result codes to zero in object map update path
Commit: 14995c4250f04b58bf6fc00e0e973a2e1b3cfb9b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=14995c4250f04b58bf6fc00e0e973a2e1b3cfb9b

Commit description:

In a reply message to an RBD request, a positive result code indicates
a data payload, which is not allowed for writes. While
rbd_osd_req_callback() already resets a positive result code for writes
to zero, rbd_object_map_callback() does not. This allows a corrupted
reply to an object map update to trigger the rbd_assert(*result < 0) in
__rbd_obj_handle_request(). This happens, because
rbd_object_map_callback() calls rbd_obj_handle_request() ->
__rbd_obj_handle_request() and passes this positive result code. From
__rbd_obj_handle_request(), rbd_obj_advance_write() is called, which
leaves the positive result code unchanged and returns true. Therefore,
the if(done && *result) branch is executed in __rbd_obj_handle_request()
and the assertion triggers.

This patch fixes the issue by adjusting the logic in the
rbd_object_map_callback() path. A positive result code for an object map
update is now reset to zero (similar to rbd_osd_req_callback()), and the
message is subsequently handled the same way as if the result code was
zero from the beginning. Additionally, a WARN_ON_ONCE() is added for
this case.

Cc: stable@vger.kernel.org
Fixes: 22e8bd5 ("rbd: support for object-map and fast-diff")
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:
  drivers/block/rbd.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=14995c4250f04b58bf6fc00e0e973a2e1b3cfb9b

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

The original Linux kernel CVE announcement for CVE-2026-68131 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68131

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:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 6.5

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: 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).