* [CVE-2026-89526][IMPORTANT] svcrdma: Validate Read chunk positions before reconstruction
@ 2026-09-12 6:06 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-12 6:06 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-89526
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: svcrdma: Validate Read chunk positions before reconstruction
Commit: 5ab3f6d882fe07ae5e61d0bcfeea00b9409155c2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5ab3f6d882fe07ae5e61d0bcfeea00b9409155c2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89526
Analysis date: Sat, 12 Sep 2026 02:06:31 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89526 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89526
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.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-89526 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-89526 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:H/I:N/A:H';CWE-125;CWE-190;*CWE-20;*CWE-200;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L';BEST CVSS score: '8.1';DESCR 'An out-of-bounds read in the RPC/RDMA server path can occur because client supplied Read chunk positions are stored and later used to split or interleave the inline RPC body without sufficient bounds checks. A remote RPC/RDMA client can send a malformed Read chunk list with a position beyond the inline body or with overlapping chunks, causing unsigned length underflow and copying data past the receive buffer into request pages that may be returned through the Reply channel. For the CVSS the PR:N is used because the attacker only needs reachability to the exposed RPC/RDMA service and no local account on the server. The issue is network reachable on systems that expose NFS over RDMA or other RPC/RDMA services, but these deployments are typically limited to trusted storage or data center networks rather than the public Internet. Impact includes kernel memory disclosure and possible denial of service, with no concrete arbitrary write primitive shown by the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 7) YES REMOTE OOB NETWORK KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=7
ActionableScoreLower=6
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 6
* Conservative score: 6. No floor or cap changed it.
* Raw paranoid score: 7
* Paranoid score: 7. No floor or cap changed it.
* Final recommended bucket: **Strong Important candidate**::
2. Signal breakdown
Conservative positive signals:
* +2 Strong primitive. Client supplied RPC/RDMA Read chunk positions can cause out of bounds reads from memory adjacent to the receive buffer.
* +2 Remote reachable / network-triggerable. The malformed Read chunk list is supplied by a remote RPC/RDMA client to the server path.
* +1 Confidentiality plausible. The copied bytes can be placed into request pages that are returned to the client through the Reply channel.
* +1 Memory layout invariant restoration. The patch restores consistency between inline body length, offsets, and computed copy lengths, preventing unsigned underflow and out of bounds copy ranges.
Paranoid additional signal:
* +1 Availability concern. The same unsigned underflow and out of bounds copying path can plausibly destabilize RPC/RDMA request processing or crash the kernel, but this is secondary to the concrete disclosure primitive.
Non-awarded signals:
* RealUAF not awarded. No object lifetime violation or stale post-free use is established.
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Integrity impact not awarded. The patch supports out of bounds read and copied disclosure, not unauthorized modification.
* Privilege escalation not awarded. No LPE or credential manipulation path is established.
* Broad/default subsystem bonus not awarded. RPC/RDMA and NFS over RDMA are important but usually deployed in storage or data-center fabrics rather than universally exposed.
* No race penalty. This is malformed input validation and unsigned length underflow, not a timing race.
* No rare hardware penalty. RDMA deployment is specialized, but the vulnerable service is a network protocol endpoint when enabled.
3. Reachability analysis
The attacker is a remote RPC/RDMA client that can reach the vulnerable server endpoint. No local account on the server is needed, so HostAdminRequired=NO.
The complete trigger is not namespace-scoped and does not depend on attacker-owned local namespaces, so NamespaceScopedPrivilege=NO.
A prior administrator must normally enable and expose NFS over RDMA or another RPC/RDMA service, but that is service deployment rather than a privilege required by the attacker once the endpoint is reachable.
The issue is not Internet-common in typical deployments. RPC/RDMA services are usually limited to trusted storage, HPC, or data-center networks. That limits operational exposure but does not remove the remote unauthenticated protocol-input primitive for reachable clients.
No special race is required. The bug is driven by supplied chunk positions and overlap or out-of-range conditions.
4. Primitive and severity interpretation
The exact primitive is an attacker-controlled out of bounds read caused by insufficient validation of Read chunk position fields and unsigned subtraction underflow.
This is not fixed stale storage and not a cleanup-only crash path. The vulnerable code copies data past the decoded inline RPC body into request pages, and the commit states those pages can be returned to the client through the Reply channel.
PrimitiveClass=CLASS_A because the patch context establishes a concrete kernel memory disclosure path, not merely an internal invalid read.
The demonstrated consequence is kernel memory disclosure to a remote RPC/RDMA client. A denial of service is plausible from malformed copy ranges, but arbitrary write, controlled corruption, and privilege escalation are not established.
ImportantCandidate=YES because this is a network-reachable kernel memory disclosure primitive in a server protocol path.
AutoDowngradeAllowed=NO because automatically downgrading would lose a concrete remote disclosure primitive with meaningful security impact.
Likely operational severity is high in environments where RPC/RDMA is reachable by untrusted or semi-trusted clients, and lower in tightly isolated storage fabrics.
5. One-sentence report phrase
A remote RPC/RDMA client can supply invalid Read chunk positions that trigger unsigned length underflow and out of bounds reads, causing kernel memory disclosure through reply pages and possibly denial of service.
6. Manual review recommendation
MANUAL CHECK REQUIRED
Manual review is required because the patch establishes a concrete remotely reachable kernel memory disclosure primitive, even though arbitrary write and privilege escalation are not shown.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: svcrdma: Validate Read chunk positions before reconstruction
Commit: 5ab3f6d882fe07ae5e61d0bcfeea00b9409155c2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5ab3f6d882fe07ae5e61d0bcfeea00b9409155c2
Commit description:
The RPC/RDMA Read chunk position field is supplied by the remote
client and stored verbatim in the parsed chunk list.
xdr_count_read_segments() checks only 4-byte alignment; it never
compares the position against the received inline body length.
In the single-chunk path, svc_rdma_read_complete_one() splits the
head and tail kvecs at ch_position. A position past the inline
body underflows the tail length, exposing adjacent slab memory to
the upper XDR decoder.
In the multi-chunk path, svc_rdma_read_multiple_chunks() computes
gap lengths between chunks as unsigned subtractions from
ch_position. Overlapping Read chunks cause these subtractions to
underflow. A final position past the inline body likewise
underflows the trailing gap length. svc_rdma_copy_inline_range()
then copies past the receive buffer into request pages that are
returned to the client through the Reply channel.
Bound inline-range copies in svc_rdma_copy_inline_range() against
the decoded inline RPC body saved in rc_saved_arg. Reject a
single Read chunk positioned beyond that body, and reject
multi-chunk lists where accumulated read bytes exceed the next
chunk's position. Apply the same position and overlap checks in
the call-chunk interleaving path.
Fixes: d96962e ("svcrdma: Use the new parsed chunk list when pulling Read chunks")
Cc: [email protected]
Acked-by: Jeff Layton <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Chuck Lever <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
net/sunrpc/xprtrdma/svc_rdma_rw.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=5ab3f6d882fe07ae5e61d0bcfeea00b9409155c2
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89526 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89526
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:L/PR:N/UI:N/S:U/C:H/I:N/A:L
The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
The Best / paranoid CVSS score: 8.1
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: 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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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