* [CVE-2026-89529][MODERATE 7.0] svcrdma: Reject oversized Read segments at decode time
@ 2026-09-12 2:36 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-12 2:36 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-89529
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: svcrdma: Reject oversized Read segments at decode time
Commit: 5120fe54e0e2f5b62797a432115cc61d61117a5b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5120fe54e0e2f5b62797a432115cc61d61117a5b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89529
Analysis date: Fri, 11 Sep 2026 22:36:34 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89529 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89529
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-2026-89529 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89529 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-20;CWE-770;*CWE-772;**CWE-400;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '6.5';DESCR 'An oversized RPC RDMA Read segment can reach svc_rdma_build_read_segment because the Read list decoder stores the wire supplied segment length without bounding it against the receive context page budget. This can drive a large dynamic bvec allocation and then hit the page overrun path after allocation. The overrun path also failed to return the acquired rw context, so repeated malformed requests can leak resources and create memory pressure. For the CVSS the PR:N is selected because a remote RPC RDMA client can supply the malformed Read segment to the target service without local code execution on the victim. The issue is network reachable only where RPC RDMA service is exposed over an RDMA capable storage or data center network, so AV:A is used rather than AV:N. Impact is denial of service via resource exhaustion. No concrete UAF, OOB write, or arbitrary write primitive is shown by the code change.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) SKIP CVE-2026-89529 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE REMOTE SIMPLEFIX LEAK NETWORK KPANIC KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6 - - guess
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=4
ActionableScoreLower=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: 4
* Paranoid score: 4. No floor or cap applied.
* Final recommended bucket: **Borderline / manual review recommended**::
2. Signal breakdown
Conservative positive signals:
* +2 Remote or network reachable operation. The malformed Read segment is supplied over RPC/RDMA to the server transport path.
* +1 Concrete persistent kernel resource/reference leak. The post-allocation page-overrun path failed to return the acquired rw context.
Paranoid additional signal:
* +1 Availability impact from sustained resource exhaustion. Repeated oversized Read segments can drive large bvec allocations and leak rw contexts, making service or host resource exhaustion technically plausible.
Non-awarded signals:
* Real UAF not awarded. The patch shows oversized length handling and missing rw context release, not stale post-lifetime object use.
* Controlled reclaim not demonstrated.
* Arbitrary or directed kernel write not demonstrated.
* Confidentiality and integrity impact not awarded. The established primitive is allocation pressure plus resource leak, not disclosure or unauthorized modification.
* Strong LPE or weak LPE concern not awarded. No exploitation primitive beyond DoS/resource exhaustion is established.
* No race or timing penalty applied. The bug is an ordered invalid-input/error-path resource leak, not a narrow timing race.
* No subsystem rarity penalty applied. RDMA deployment limits exposure, but specialization alone is not concrete evidence for a score reduction.
* Extra availability was not double-counted. Conservative score counts the leak itself, while paranoid score adds only the sustained exhaustion consequence.
3. Reachability analysis
A remote RPC/RDMA client can supply an oversized wire Read segment to an exposed RPC/RDMA service. This does not require local code execution or host administrator privilege on the victim, so HostAdminRequired=NO. The realistic network scope is not the public Internet in most deployments. RPC/RDMA is normally used in storage or data-center RDMA networks, so the practical attacker usually needs access to that RDMA-capable network.
Namespace-scoped privilege is not relevant to the supplied path. There is no evidence that a namespace capability is required or that namespace-local privilege is part of the trigger. Prior server configuration is a deployment prerequisite, but the supplied evidence does not show that the attacker must perform privileged local setup. No special race is needed.
4. Primitive and severity interpretation
The exact primitive is unchecked wire-supplied segment length leading to large dynamic bvec allocation and a missing release of an acquired rw context on the page-overrun error path. This is a resource/reference leak and resource-exhaustion primitive, not memory corruption.
PrimitiveClass=CLASS_C because the demonstrated behavior is DoS/resource exhaustion without an independently useful corruption, lifetime, ownership, authorization, or semantic-reinterpretation primitive. RealUAF=NO because no object is shown to be used after free. ImportantCandidate=NO because there is no unresolved Class A or strong Class B primitive. AutoDowngradeAllowed=YES because the issue can be handled as resource-exhaustion DoS if product exposure is low, although network-facing RDMA deployments should still review it.
Likely operational severity is actionable for systems exposing RPC/RDMA to untrusted or semi-trusted storage networks, but not an Important-class kernel corruption issue based on the supplied evidence.
5. One-sentence report phrase
An oversized RPC/RDMA Read segment can cause large bvec allocation and leak an rw context on an error path, allowing a remote client on an exposed RDMA storage network to cause denial of service through resource exhaustion.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Reason: the issue is network reachable in RPC/RDMA deployments and involves attacker-controlled allocation size plus a concrete resource leak, but no UAF, arbitrary write, information disclosure, authorization bypass, or privilege-escalation primitive is established.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: svcrdma: Reject oversized Read segments at decode time
Commit: 5120fe54e0e2f5b62797a432115cc61d61117a5b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5120fe54e0e2f5b62797a432115cc61d61117a5b
Commit description:
The RPC/RDMA Read list decoder stores wire-supplied segment
lengths without validation. xdr_count_read_segments() checks
4-byte alignment for non-zero position values but does not
cap the segment length.
An oversized rs_length reaches svc_rdma_build_read_segment(),
which derives nr_bvec from it and can drive a large dynamic
bvec allocation before verifying that enough rq_pages remain.
If the post-allocation page-overrun guard fires, the freshly
acquired rw context is not returned, leaking the resource.
Reject any segment whose length exceeds the receive context's
page budget during Read list decoding, consistent with how
xdr_check_write_chunk() bounds Write segment counts against
rc_maxpages. Also return the rw context on the existing
post-allocation overrun path in svc_rdma_build_read_segment(),
keeping that defensive guard balanced.
Fixes: 5ee62b4 ("svcrdma: use bvec-based RDMA read/write API")
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_recvfrom.c
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=5120fe54e0e2f5b62797a432115cc61d61117a5b
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89529 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89529
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:N/I:N/A:L
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: 3
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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