From: AL-KERNEL <[email protected]>
To: [email protected]
Subject: [CVE-2026-98250][MODERATE 7.0] nfsd: fix handling of NFSEXP_PNFS in the netlink codepath
Date: Sun, 11 Oct 2026 01:52:07 -0400 [thread overview]
Message-ID: <[email protected]> (raw)
CVE: CVE-2026-98250
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: nfsd: fix handling of NFSEXP_PNFS in the netlink codepath
Commit: 30335038d4e25cf017abb0562f4f4eace4f58f96
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=30335038d4e25cf017abb0562f4f4eace4f58f96
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98250
Analysis date: Sun, 11 Oct 2026 01:52:07 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98250 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98250
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-2026-98250 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98250 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE AEGIS_AS=0 LEGACY=MODERATE_KPANIC RESULT=DIFF (independent Legacy and Aegis differ; FINAL: MODERATE_KPANIC, Aegis: MODERATE) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';CWE-284;CWE-693;CWE-670;Other CVSS 'AV:A/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L';BEST CVSS score: '5.9';DESCR 'The nfsd netlink export path can call nfsd4_setup_layout_type even when NFSEXP_PNFS is not set. This can populate pNFS layout types for an export where the administrator did not request pNFS and may expose layout information or permit an unintended direct storage access path. For the CVSS the PR:L reflects that an attacker normally needs authorized access to the affected NFS export before requesting layouts. The attack is best treated as AV:A because practical exploitation normally also depends on access to a trusted NFS or storage network and a pNFS capable backing filesystem. Impact can include a limited confidentiality or integrity policy bypass and availability impact if unintended block layout access interferes with storage operations. No UAF, OOB access, or other kernel memory corruption primitive is indicated by the affected code. The issue requires manual review because the effective impact depends on the configured layout type, client permissions, and access to the backing storage network.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE DISK SIMPLEFIX NETWORK HARDWARE LINUS KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=YES
ProtectedResourceImpact=UNRESOLVED
B4PendingReview=YES
B4PendingConfirmed=NO
1. ActionableScore
* Raw conservative score: 3
* Conservative score: 5
* Raw paranoid score: 4
* Paranoid score: 5
* Applied conservative manual-review safety floor: 3 -> 5 because the omitted NFSEXP_PNFS policy guard can enable externally usable pNFS layout functionality.
* Applied paranoid manual-review safety floor: 4 -> 5 for the same unresolved authorization-boundary consequence.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
Conservative signals:
* +2 Concrete authorization decision bypass. The netlink export path calls nfsd4_setup_layout_type even when NFSEXP_PNFS is absent, changing the effective pNFS decision from disabled to enabled.
* +1 Important filesystem/storage path. The affected state controls NFSv4 pNFS layouts and potentially layout-based block-device access.
* Total: 3.
Additional paranoid signal:
* +1 Practical external consequence is strongly implied. Once such an export exists, an authorized NFSv4 client can request layouts and potentially receive a direct storage layout that the administrator did not enable.
* Total: 4.
Not awarded:
* No UAF, OOB access, arbitrary write, controlled reclaim, or kernel-memory corruption is established.
* No confidentiality point because disclosure of protected file contents or storage credentials is not demonstrated.
* No integrity point because unauthorized modification of a specific protected object or backing device is not established.
* No remote-reachability +2 because the vulnerable state first requires a host administrator to create an export through the affected netlink path.
* No B3-PENDING shared-backing write and no B5-R retry-accumulated OOB write.
* No crash or availability point because the patch does not establish a panic, storage shutdown, or reliable service failure.
* No privilege penalty applies to the subsequent client operation. Prior host-admin export configuration is a deployment prerequisite, not a privilege held by the NFS client exercising the unintended layout path.
3. Reachability analysis
A host administrator must first create or update an NFS export through the affected netlink interface without NFSEXP_PNFS. That is prior privileged setup.
Afterward, the relevant attacker is an authorized NFSv4 client rather than the export-management process. Such a client is below host-admin privilege and can ordinarily issue pNFS layout requests. This supports HostAdminRequired=NO for the security-relevant client operation, while recognizing the separate privileged setup prerequisite.
The complete path is not namespace-capability based, so NamespaceScopedPrivilege=NO. Practical exploitation also depends on a pNFS-capable filesystem and may require access to the associated storage network for block layouts. Public Internet exposure is not established.
4. Primitive and severity interpretation
The primitive is a concrete configuration-policy bypass: the NFSEXP_PNFS guard is omitted in nfsd_nl_parse_one_export, allowing nfsd4_setup_layout_type to populate layout capabilities for an export where pNFS was not requested.
This is CLASS_A as an authorization-policy decision bypass, not as memory corruption. It changes the effective decision from pNFS disabled to pNFS layout functionality enabled.
B4PendingReview=YES because a credible below-host-admin client path exists and the missing guard affects externally usable layout behavior. B4PendingConfirmed=NO because the supplied evidence does not identify a specific protected file, block device, credential, or other sensitive resource that the client can access beyond its normal NFS authority.
The practical consequence is an unintended direct-storage access path or layout-information exposure. Protected-resource impact remains unresolved, and privilege escalation is not demonstrated.
ImportantCandidate=YES and AutoDowngradeAllowed=NO because automatically treating this as an ordinary configuration defect could discard a meaningful storage-policy boundary bypass. Manual review should determine which layout types become enabled, whether LAYOUTGET succeeds without NFSEXP_PNFS, and whether block layouts expose access beyond ordinary NFS permissions.
5. One-sentence report phrase
The nfsd netlink export path can enable pNFS layout types without NFSEXP_PNFS, potentially allowing an authorized NFS client to obtain an unintended direct-storage layout while the resulting protected-resource impact remains unresolved.
6. Manual review recommendation
MANUAL CHECK REQUIRED
Verify the downstream LAYOUTGET behavior, enabled layout types, storage-network authorization, and whether block-layout access crosses the permissions intended by the NFS export.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: nfsd: fix handling of NFSEXP_PNFS in the netlink codepath
Commit: 30335038d4e25cf017abb0562f4f4eace4f58f96
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=30335038d4e25cf017abb0562f4f4eace4f58f96
Commit description:
The rework of how block layouts were checked moved the check for
NFSEXP_PNFS out of nfsd4_setup_layout_type() and into the callers. That
patch didn't account for the new call in nfsd4_setup_layout_type().
Cc: Christoph Hellwig <[email protected]>
Fixes: da9baa5 ("exportfs,nfsd: rework checking for layout-based block device access support")
Cc: [email protected]
Reported-by: Olga Kornievskaia <[email protected]>
Signed-off-by: Jeff Layton <[email protected]>
Reviewed-by: Christoph Hellwig <[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:
fs/nfsd/export.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=30335038d4e25cf017abb0562f4f4eace4f58f96
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98250 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98250
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:H/PR:L/UI:N/S:U/C:L/I:L/A:L
The Best / paranoid CVSS vector: AV:A/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
The Best / paranoid CVSS score: 5.9
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: 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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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