[CVE-2026-89505][MODERATE REGULAR] RDMA/uverbs: Guard legacy bundles without method_elm

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

CVE: CVE-2026-89505
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: RDMA/uverbs: Guard legacy bundles without method_elm
Commit: edae84e5461749ed9adf9fcf5c6e075381040ac3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=edae84e5461749ed9adf9fcf5c6e075381040ac3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89505
Analysis date: Sat, 12 Sep 2026 03:39:10 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
A local RDMA uverbs user can trigger an uninitialized method_elm pointer dereference through malformed legacy write input, causing a kernel crash, but no UAF, arbitrary write, information disclosure, or privilege escalation primitive is established.

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

The original Linux kernel CVE announcement for CVE-2026-89505 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89505

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-2026-89505	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89505 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H';CWE-824;*CWE-457;**CWE-476;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.1';DESCR 'A wild pointer dereference in RDMA uverbs can occur because the legacy write path builds a uverbs_attr_bundle without a valid ioctl method element and leaves method_elm uninitialized. If malformed provider input makes the common uverbs validation code emit an error message, uverbs_get_handler_fn can dereference this uninitialized pointer and crash the kernel. For the CVSS the PR:L value is used because a local user or process needs access to the RDMA uverbs device node such as /dev/infiniband/uverbs. The issue is not network reachable by itself and is triggered through a local character device interface rather than remote packet traffic. Impact is at least local denial of service via kernel crash. For the paranoid score, limited confidentiality impact is kept as a review sensitive interpretation because the bug reads through an uninitialized kernel pointer, but there is no clear arbitrary write primitive in the provided patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)  SKIP CVE-2026-89505 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	WRITE OOB SIMPLEFIX NETWORK  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=3
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

## 1. ActionableScore

* Raw conservative score: 3
* Conservative score: 3. No floor or cap applied.
* Raw paranoid score: 3
* Paranoid score: 3. No additional paranoid point is awarded because no controlled reclaim, disclosure path, arbitrary write, callback control, or lifetime mutation is established.
* Final recommended bucket: **Borderline / manual review recommended**::

## 2. Signal breakdown

Positive signals:

* +1 Local below-host-admin trigger. A local process with access to `/dev/infiniband/uverbs*` can submit malformed legacy uverbs write input.
* +1 Weak / indirect invalid pointer primitive. `bundle.method_elm` is uninitialized in the legacy write path, and `uverbs_get_handler_fn()` can dereference it.
* +1 Reliable kernel crash / strong DoS. A wild or invalid `method_elm` dereference can fault in kernel context.

Non-awarded signals:

* Real UAF not awarded. The patch shows an uninitialized pointer dereference, not post-free object use.
* Concrete repeated release/refcount not awarded. There is no first put/free followed by a second lifetime mutation on the same dangling reference.
* Controlled reclaim not demonstrated.
* Arbitrary or directed kernel write not demonstrated.
* Callback/function-pointer control not demonstrated. The visible issue is dereferencing `method_elm` to read `handler`, not a demonstrated attacker-controlled indirect call.
* Confidentiality not awarded. No user-visible disclosure path is established.
* Integrity not awarded. No unauthorized modification primitive is established.
* Remote reachability not awarded. This is a local uverbs character device path, not packet-triggered RDMA network traffic.
* Extra Availability not awarded because the same kernel fault is already counted once.

## 3. Reachability analysis

The evaluated attacker is a local user or local process that can open the RDMA uverbs device node and issue legacy write commands. This is below host-admin if device permissions grant uverbs access, which is normal for user verbs deployments, so `HostAdminRequired=NO`.

The complete trigger is not shown to be namespace-scoped. It depends on access to the RDMA uverbs character device rather than CAP_NET_ADMIN inside a network namespace, so `NamespaceScopedPrivilege=NO`.

No direct network trigger is established. Remote RDMA traffic alone is not shown to reach this path. The vulnerable operation is a local userspace ABI path through `ib_uverbs_write()`.

A prior loaded RDMA provider/device is required, but the evidence does not justify a rare-hardware penalty. No race or narrow timing requirement is involved.

## 4. Primitive and severity interpretation

The exact primitive is an uninitialized kernel pointer dereference. The legacy write path creates a `uverbs_attr_bundle` without an ioctl method element, and malformed provider input can cause common validation/error handling code to call `uverbs_get_handler_fn()`, which dereferences `bundle->method_elm`.

This is not an active-object UAF and not fixed stale storage. It is also not a cleanup/destructor lifetime issue. There is no concrete repeated release/refcount operation.

Primitive class is `CLASS_C`: demonstrated behavior is primarily invalid pointer dereference and kernel crash. The demonstrated consequence is local denial of service. A stronger consequence such as LPE is speculative and not supported by the supplied patch.

`ImportantCandidate=NO` because no independently useful corruption primitive is established beyond the crash path. `AutoDowngradeAllowed=YES` because the issue is a constrained local crash primitive with no UAF, no repeated lifetime mutation, no authorization bypass, no controlled corruption, and no demonstrated C/I impact.

Likely operational severity is borderline Moderate: worth manual review because it is local user reachable kernel memory-safety behavior, but not enough for Important-class triage without additional exploit evidence.

## 5. One-sentence report phrase

A local RDMA uverbs user can trigger an uninitialized method_elm pointer dereference through malformed legacy write input, causing a kernel crash, but no UAF, arbitrary write, information disclosure, or privilege escalation primitive is established.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: local user reachable wild pointer dereference in kernel RDMA code should be reviewed, but current evidence supports crash-only impact and does not establish Important-grade exploitation leverage.

## 7. Call-site confidence

Call-site confidence: medium

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

Patch: RDMA/uverbs: Guard legacy bundles without method_elm
Commit: edae84e5461749ed9adf9fcf5c6e075381040ac3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=edae84e5461749ed9adf9fcf5c6e075381040ac3

Commit description:

The legacy write() path dispatches through a uverbs_api_write_method, but
the uverbs_attr_bundle passed to provider code does not have an ioctl
method element. If malformed provider input causes the common uverbs
validation code to emit an error message, uverbs_get_handler_fn()
dereferences the uninitialized method_elm pointer.

Initialize method_elm explicitly for legacy bundles and make
uverbs_get_handler_fn() return NULL when no ioctl method is present. The
legacy dispatcher continues to use its local write method, while the ioctl
path continues to use the registered ioctl handler.

Cc: stable@vger.kernel.org
Fixes: 7122ff9 ("RDMA/core: Do not read wild stack memory in uverbs_get_handler_fn()")
Link: https://patch.msgid.link/r/AOYAQgCQK3IXqJLr1TB5Qao9.1.1787036796115.Hmail.242270054@hdu.edu.cn
Signed-off-by: Yuhang Pan <242270054@hdu.edu.cn>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/infiniband/core/ib_core_uverbs.c
  drivers/infiniband/core/uverbs_main.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=edae84e5461749ed9adf9fcf5c6e075381040ac3

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

The original Linux kernel CVE announcement for CVE-2026-89505 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89505

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:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H
  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: unknown
  Paranoid ActionableScore: 3

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).