* [CVE-2026-90148][MODERATE REGULAR] NFSv4: Fix incorrect argument passed to nfs4_delete_lease() in nfs4_add_lease() [ Upstream
@ 2026-09-18 2:47 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-18 2:47 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-90148
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: NFSv4: Fix incorrect argument passed to nfs4_delete_lease() in nfs4_add_lease() [ Upstream
Commit: ff7244faa13b23e9acfad9df0438f0b44b338f62
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ff7244faa13b23e9acfad9df0438f0b44b338f62
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90148
Analysis date: Thu, 17 Sep 2026 22:47:49 -0400
ActionableScore: 3
ActionableScore lower bound: 2
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-2026-90148 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90148
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.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-90148 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-90148 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-362;CWE-754;BEST CVSS score: '4.7';DESCR 'A race in NFSv4 lease setup can occur when nfs4_add_lease() races with a delegation return and enters the cleanup path. The old code passed priv to nfs4_delete_lease(), but priv may legitimately be NULL and can later cause a NULL pointer dereference in generic_setlease(). For the CVSS the PR:L is used because a local user or local process able to request file leases on an affected NFSv4 mount is needed for practical triggering. The issue is not directly network reachable as a packet processing bug, although it depends on NFSv4 delegation behavior between the client and server. Impact is local denial of service via kernel crash. No confidentiality or integrity impact is assigned because the visible primitive is a NULL pointer dereference rather than UAF, OOB access, or an arbitrary write.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) YES NULLPTR DISK SIMPLEFIX RACE NETWORK LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 3
* Paranoid score: 3
* Final recommended bucket: **Borderline / manual review recommended**::
No floor or cap was applied. Conservative score applies the race timing penalty. Paranoid score withholds that penalty because repeated local lease attempts plus delegation behavior may make the race more reachable than a one-shot teardown race.
2. Signal breakdown
Positive signals:
* +1 Local unprivileged trigger: a local user or process able to request file leases on an affected mounted NFSv4 filesystem can reach nfs4_add_lease().
* +1 Reliable kernel crash / strong DoS: passing NULL priv to nfs4_delete_lease() can eventually cause NULL pointer dereference in generic_setlease().
* +1 Important filesystem/storage path: the issue is in NFSv4 client lease/delegation handling, a real filesystem/storage control path.
Negative signals:
* -1 Hard or unreliable race for conservative score: the failure requires a race between nfs4_add_lease() and delegation return, which is timing dependent.
Important non-awarded signals:
* RealUAF not awarded: the established primitive is NULL pointer dereference, not stale post-lifetime object use.
* Concrete repeated release/refcount not awarded: the patch does not establish first release ending lifetime followed by a second lifetime mutation on the same dangling reference.
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Confidentiality and integrity not awarded: no disclosure path, protected-object read, unauthorized write, UAF, OOB access, or arbitrary write is established.
* Extra Availability not awarded: the crash/DoS is already counted once.
* Remote reachability not awarded: NFS server delegation behavior participates, but this is not direct packet-processing reachability by a remote attacker against the vulnerable operation.
3. Reachability analysis
The practical trigger is local on the NFS client. The attacker needs to run code that requests a file lease on an affected NFSv4 mount while delegation state changes concurrently. This is below host-admin in the evaluated model because lease requests can be made by a local process with suitable file access on an already mounted filesystem.
A prior NFSv4 mount and delegation-capable setup are needed, but the supplied evidence does not show that the attacker must be host administrator to use the vulnerable lease path once the mount exists. Namespace-scoped privilege is not relevant and is set to NO. The complete trigger is not established as namespace-created or namespace-contained.
The bug is not directly network reachable as a packet-processing vulnerability. A malicious or controlled NFS server might influence delegation return timing, but the complete trigger still depends on local client lease setup. The race is timing dependent. Conservative scoring treats it as hard, while paranoid scoring allows for repeated local attempts.
No special hardware is required.
4. Primitive and severity interpretation
The exact primitive is an invalid NULL pointer dereference caused by passing priv to nfs4_delete_lease() even though priv may legitimately be NULL. The downstream failure occurs in generic_setlease().
This is not an active structured UAF and not fixed stale storage. It is a race-triggered invalid cleanup argument leading to crash. The stale/lifetime conditions required for RealUAF are not established. There is no concrete repeated release/refcount operation: the patch changes which owner pointer is passed to cleanup, but does not show a first lifetime-ending release followed by a second release of the same dangling object.
PrimitiveClass is CLASS_C because demonstrated behavior is crash/DoS through NULL dereference without an independently useful corruption primitive. Demonstrated consequence is local denial of service via kernel crash. Speculative privilege escalation is not supported by the patch or supplied context.
ImportantCandidate is NO because no memory corruption, authorization bypass, COW/ownership violation, controlled reclaim, arbitrary R/W, or repeated lifetime mutation is established. AutoDowngradeAllowed is YES because this is a constrained crash-only Class C issue, although manual review is still recommended due to the race in NFSv4 lease/delegation state.
Likely operational severity is ordinary Moderate to borderline Moderate.
5. One-sentence report phrase
A race in NFSv4 lease setup can pass a NULL cleanup owner into nfs4_delete_lease() during delegation return, leading to a NULL pointer dereference in generic_setlease() and local kernel crash.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Reason: the issue is a kernel race in NFSv4 lease/delegation handling and can crash the client, but current evidence supports NULL dereference DoS only and does not establish UAF, C/I impact, or privilege escalation.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: NFSv4: Fix incorrect argument passed to nfs4_delete_lease() in nfs4_add_lease() [ Upstream
Commit: ff7244faa13b23e9acfad9df0438f0b44b338f62
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ff7244faa13b23e9acfad9df0438f0b44b338f62
Changed files:
fs/nfs/nfs4proc.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=ff7244faa13b23e9acfad9df0438f0b44b338f62
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90148 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90148
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:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 4.7
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: 2
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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