[CVE-2026-89528][MODERATE 7.0] svcrdma: Reject Read lists that exceed the page budget [ Upstream

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

CVE: CVE-2026-89528
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: svcrdma: Reject Read lists that exceed the page budget [ Upstream
Commit: 1a3af2262cb384112ef38632de4690682be528b4
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1a3af2262cb384112ef38632de4690682be528b4
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89528
Analysis date: Sat, 12 Sep 2026 06:19:54 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89528 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89528

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.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-89528	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89528 CHECK WITH IMPACT FROM ORIG NN MODERATE	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-20;**CWE-476;CWE-770;BEST CVSS score: '6.5';DESCR 'An RPC/RDMA Read list handling flaw in svcrdma can cause a NULL-pointer dereference because each Read segment length is checked individually but the cumulative length across all segments is not bounded by the receive page budget. A remote RDMA peer can send multiple Read segments whose total size exceeds the rq_pages array budget. When one segment exactly consumes the page array, the following segment reaches the rq_pages sentinel slot and the server later dereferences a NULL page pointer during DMA mapping, causing a kernel crash (DoS). For the CVSS the PR:N is selected because a peer only needs network reachability to the NFS/RDMA service and no local account on the victim is required. The issue is network reachable only on systems that expose the RPC/RDMA or NFS/RDMA service, typically on storage or data center RDMA networks rather than the public Internet. Impact is denial of service via kernel crash, with no grounded evidence of information disclosure or privilege escalation from this patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	YES	REMOTE NULLPTR SIMPLEFIX NETWORK DMAorINTERRUPT KPANIC 	NO	NO	checked

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

ActionableScore=4
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=REQUIRED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 4
* Raw paranoid score: 4
* Paranoid score: 4
* No floor or cap changed the score.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Positive signals:

* +2 Remote reachable / directly network-triggerable: an RPC/RDMA or NFS/RDMA requester can send a malformed Read list to an exposed svcrdma service.
* +1 Reliable kernel crash / strong DoS: the commit explicitly states that the overflowed Read list can reach the NULL sentinel at rq_pages[rq_maxpages] and cause a NULL pointer dereference during DMA mapping.
* +1 Memory layout / length-budget invariant restoration: the patch restores consistency between cumulative Read segment lengths and the rq_pages array budget by checking PAGE_ALIGN(total_len) against maxlen.

Negative signals:

* 0 No host-admin penalty: the attacker does not need local host administration once the RPC/RDMA service is reachable.
* 0 No race penalty: this is an ordered malformed input validation failure, not a timing race.
* 0 No rare-subsystem penalty: NFS/RDMA is specialized and often internal, but the prompt requires concrete evidence before subtracting for deployment rarity.

Important non-awarded signals:

* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Real UAF not established.
* Concrete repeated release/refcount operation not established.
* Confidentiality and integrity impact not awarded because the established primitive is a NULL pointer dereference crash.
* Extra Availability not awarded because the same kernel crash is already counted once.
* Strong LPE or privilege escalation not awarded.
* ImportantCandidate is not set because this is a crash-only Class C primitive without unresolved memory-corruption leverage.

3. Reachability analysis

The evaluated attacker is a remote RPC/RDMA peer that can reach the NFS/RDMA service. No local account on the victim is required, so HostAdminRequired=NO.

The complete trigger requires that the target system has svcrdma / NFS over RDMA enabled and reachable. This is prior service exposure, not attacker privilege on the victim. In practice these services are usually deployed on storage or data-center RDMA networks rather than the public Internet, but that limits exposure rather than changing the primitive.

Namespace-scoped privilege is not relevant to the complete trigger, so NamespaceScopedPrivilege=NO. No sysctl, boot option, or local capability requirement for the attacker is shown. RDMA-capable infrastructure is required for exposure, but this is not enough to apply a physical-only or rare-hardware penalty under the provided rules. The trigger is not a race and should be repeatable with malformed protocol input.

4. Primitive and severity interpretation

The exact primitive is missing cumulative bounds validation for RPC/RDMA Read segments. Individual segment lengths were checked, but the sum of multiple segments could exceed the receive page budget. When the page array is exactly consumed, the next segment can cause access to the NULL sentinel slot and later dereference a NULL page pointer during DMA mapping.

This is not an active structured UAF and not fixed stale storage. It is a malformed input / invalid state / NULL dereference path. There is no concrete repeated release/refcount operation. The first lifetime operation, second lifetime mutation, and dangling reference requirements do not apply.

PrimitiveClass=CLASS_C because the demonstrated behavior is kernel crash / DoS without an independently useful corruption primitive. The demonstrated consequence is host kernel DoS. The speculative consequence would be stronger corruption or privilege escalation, but the patch and supplied context do not support such a mechanism.

ImportantCandidate=NO because there is no Class A primitive and no strong Class B unresolved lifetime/corruption primitive. AutoDowngradeAllowed=YES because this can be treated as non-Important after exposure review, although it should not be ignored on systems exposing NFS/RDMA.

Likely operational severity is an actionable network-adjacent DoS for exposed RPC/RDMA servers, especially inside storage networks.

5. One-sentence report phrase

A malformed RPC/RDMA Read list can exceed the svcrdma receive page budget and trigger a NULL pointer dereference during DMA mapping, allowing a reachable RDMA peer to crash the kernel.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the issue is network reachable on systems exposing RPC/RDMA or NFS/RDMA and can cause a kernel crash, even though no UAF, arbitrary write, information disclosure, or privilege escalation primitive is established.

7. Call-site confidence

Call-site confidence: high

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

Patch: svcrdma: Reject Read lists that exceed the page budget [ Upstream
Commit: 1a3af2262cb384112ef38632de4690682be528b4
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1a3af2262cb384112ef38632de4690682be528b4

Changed files:
  net/sunrpc/xprtrdma/svc_rdma_recvfrom.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=1a3af2262cb384112ef38632de4690682be528b4

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

The original Linux kernel CVE announcement for CVE-2026-89528 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89528

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: Not available
  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: unknown
  Paranoid ActionableScore: 4

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).