[CVE-2026-45856][MODERATE 7.0] RDMA/uverbs: Validate wqe_size before using it in ib_uverbs_post_send [ Upstream

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

CVE: CVE-2026-45856
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: RDMA/uverbs: Validate wqe_size before using it in ib_uverbs_post_send [ Upstream
Commit: 9c15ec4cd4e7f57c6bbcb4e73e99290f150dd2a7
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9c15ec4cd4e7f57c6bbcb4e73e99290f150dd2a7
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45856
Analysis date: Thu, 28 May 2026 00:37:11 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
`ib_uverbs_post_send()` accepted an unvalidated userspace `wqe_size`, allowing a local user with RDMA uverbs access to cause kernel heap out-of-bounds reads and possible kernel information disclosure.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-45856 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45856

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-2026-45856	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:L';CWE-125;*CWE-20;*CWE-200;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:L';BEST CVSS score: '6.1';DESCR 'RDMA/uverbs ib_uverbs_post_send used a userspace controlled wqe_size before validating that the buffer was large enough for struct ib_uverbs_send_wr. A local user with access to an RDMA uverbs device can provide a too small wqe_size, causing later reads of fields such as opcode and num_sge to go out-of-bounds on a kernel heap allocation. For the CVSS the PR:L is used because triggering requires local access to the uverbs character device or an equivalent delegated RDMA device context, not full administrative privileges. The issue is not network reachable by itself. Impact is mainly possible kernel information disclosure from an out-of-bounds read, plus limited availability impact from allocator warnings for oversized requests. There is no supported write primitive or direct privilege escalation path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) 	MAYBE	READ OOB LEAK NETWORK LINUS KPANIC  KPANIC LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS 	-	-	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:

* Local unprivileged trigger: +1. A local user with access to `/dev/infiniband/uverbsX` can provide a crafted `wqe_size`.
* Confidentiality impact plausible: +1. The bug is an out-of-bounds read from kernel heap memory and may expose sensitive kernel data.
* Availability impact realistic: +1. Excessively large `wqe_size` values can trigger allocator warnings, although this is not a strong crash primitive.
* Local high-control kernel device API: +1. RDMA uverbs is a userspace-controlled kernel device interface with structured command parsing.

Paranoid additional signal:

* Privileged kernel/device-management path: +1. The bug occurs inside RDMA core command handling, a trusted kernel/device-management path, even though the demonstrated primitive is read-only.

Not counted:

* No remote/network trigger by itself.
* No OOB write, UAF, double-free, arbitrary write, or refcount takeover.
* No demonstrated privilege escalation path.
* No strong kernel crash primitive beyond allocator warning behavior.

## 3. Reachability analysis

The attacker needs local access to an RDMA uverbs character device or an equivalent delegated RDMA context. This is commonly granted to users in RDMA/HPC/containerized accelerator environments, but it is not present on systems without RDMA hardware or exposed uverbs devices.

Namespaces and containers matter if `/dev/infiniband/uverbsX` is passed into a container. In that case, the trigger can be available to a containerized or non-root workload. The issue is not remotely reachable through RDMA networking alone unless the attacker already has local device access on the host or container.

## 4. Severity interpretation

This behaves like an actionable Moderate issue. The supported primitive is a local kernel heap out-of-bounds read with possible information disclosure, plus limited availability impact from allocator warnings.

It does not currently behave like an Important memory-corruption or LPE issue because the patch shows read beyond allocation bounds, not attacker-controlled overwrite or object lifetime corruption.

## 5. One-sentence report phrase

`ib_uverbs_post_send()` accepted an unvalidated userspace `wqe_size`, allowing a local user with RDMA uverbs access to cause kernel heap out-of-bounds reads and possible kernel information disclosure.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Kernel heap OOB reads can expose sensitive data and may assist exploit chains, especially when RDMA uverbs devices are delegated to non-root users or containers.

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

Patch: RDMA/uverbs: Validate wqe_size before using it in ib_uverbs_post_send [ Upstream
Commit: 9c15ec4cd4e7f57c6bbcb4e73e99290f150dd2a7
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9c15ec4cd4e7f57c6bbcb4e73e99290f150dd2a7

Changed files:
  drivers/infiniband/core/uverbs_cmd.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=9c15ec4cd4e7f57c6bbcb4e73e99290f150dd2a7

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

The original Linux kernel CVE announcement for CVE-2026-45856 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45856

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:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:L
  The Best / paranoid CVSS score: 6.1

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: 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).