* [CVE-2026-89710][MODERATE 7.0] NFSv4.1: fix layout segment leak on the pnfs_layout_process() forget path
@ 2026-09-12 9:04 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-12 9:04 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-89710
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: NFSv4.1: fix layout segment leak on the pnfs_layout_process() forget path
Commit: 7c5b0e813efd9124760d5fd1bfc6b229f03fb1a2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7c5b0e813efd9124760d5fd1bfc6b229f03fb1a2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89710
Analysis date: Sat, 12 Sep 2026 05:04:03 -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-2026-89710 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89710
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-2026-89710 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89710 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';*CWE-401;*CWE-772;**CWE-400;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.9';DESCR 'A memory leak in the NFSv4.1 pNFS layout processing path can occur when pnfs_layout_process handles a new layout stateid while an existing valid layout is still held. Layout segments moved to the local free_me list on the forget path are not drained, so repeated server driven layout state changes can accumulate unreleased layout segment objects on the client. For the CVSS the PR:N because the attacker does not need local privileges on the victim client, but practical triggering requires control of the NFS server endpoint or the ability to tamper with NFS traffic for a client using pNFS. The issue is network reachable only in the context of an established or trusted NFSv4.1 pNFS deployment, not as a generic Internet exposed kernel interface. Impact is denial of service through memory exhaustion. No direct confidentiality or integrity impact is indicated because the patch context shows a resource leak without a memory corruption primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) YES DISK INIT LEAK NETWORK LINUS KPANIC NO NO checked
======================================================================
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 signals:
* +1 Concrete persistent kernel resource/reference leak. The patch restores pnfs_free_lseg_list(&free_me), showing that layout segments placed on the local free_me list were not drained on the forget path.
* +2 Network-influenced remote endpoint path. A malicious or faulty NFSv4.1 pNFS server response can drive the client into the affected pnfs_layout_process() path when the client is already using that server.
Paranoid additional signal:
* +1 Sustained availability concern. Repeated server-driven layout state changes may accumulate leaked layout segments and plausibly cause memory pressure or DoS over time.
Non-awarded signals:
* RealUAF not awarded. The evidence shows missing list draining and leaked layout segments, not use after free.
* Concrete repeated release/refcount not awarded. The patch does not show a second put/free/refcount mutation through the same dangling reference.
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Confidentiality and integrity not awarded. The established primitive is resource leakage, not disclosure or unauthorized modification.
* Strong LPE or weak LPE not awarded. No memory corruption or privilege-escalation path is established.
* Reliable immediate kernel crash not awarded. The demonstrated issue is leak accumulation, not a direct panic.
* Extra Availability not double-counted beyond the paranoid sustained-exhaustion point.
3. Reachability analysis
The attacker model is a malicious, compromised, or traffic-tampering NFSv4.1 pNFS server endpoint interacting with a victim client. The attacker does not need local privileges on the victim host once the victim is already using the affected pNFS mount, so HostAdminRequired=NO for the evaluated trigger path.
There is prior deployment context: the client must be configured to use NFSv4.1 pNFS and must receive relevant layout state changes. That makes this not a generic Internet-exposed kernel interface. It is network reachable in the storage-client trust relationship.
Namespace-scoped privilege is not relevant here, so NamespaceScopedPrivilege=NO. No special local namespace capability is needed by the remote server-side attacker. No special hardware requirement is established. This is not a race. Repetition is practical if the server can repeatedly cause the affected forget path, but the impact depends on leak accumulation.
4. Primitive and severity interpretation
The exact primitive is a persistent kernel memory/resource leak of pNFS layout segment objects. Segments moved to free_me are no longer attached to the normal layout segment list, but the out_forget path failed to drain that temporary list.
This is not active structured stale-object use. It is not fixed stale storage UAF. It is not a cleanup UAF. It is a missing release/drain operation causing leaked kernel objects.
PrimitiveClass=CLASS_C because the demonstrated behavior is resource-exhaustion DoS without an independently useful corruption, ownership, authorization, or memory-lifetime exploitation primitive. RealUAF=NO.
The demonstrated consequence is memory leak and possible DoS through resource exhaustion. The speculative consequence is broader availability degradation if a malicious server can repeatedly trigger the path. There is no patch-supported path to privilege escalation, arbitrary read/write, controlled reclaim, or information disclosure.
ImportantCandidate=NO because this is a resource leak without memory corruption or security-boundary bypass. ManualReview=RECOMMENDED because the trigger is network-influenced through NFS server responses and the paranoid score reaches a borderline actionable range. AutoDowngradeAllowed=YES because no unresolved Important-grade primitive remains.
Likely operational severity is ordinary to borderline Moderate, depending on whether affected clients use pNFS with untrusted or compromised server endpoints.
5. One-sentence report phrase
A missing drain of the pNFS free_me layout segment list in pnfs_layout_process() can allow a malicious or faulty NFSv4.1 pNFS server to cause persistent client-side kernel memory leaks and potential denial of service through resource exhaustion.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Reason: the issue is network-influenced in real NFSv4.1 pNFS deployments and sustained server-side triggering may cause availability impact, but the patch supports only a resource leak and does not establish UAF, memory corruption, authorization bypass, or privilege escalation.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: NFSv4.1: fix layout segment leak on the pnfs_layout_process() forget path
Commit: 7c5b0e813efd9124760d5fd1bfc6b229f03fb1a2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7c5b0e813efd9124760d5fd1bfc6b229f03fb1a2
Commit description:
When the server returns a new layout stateid while a valid one is still
held, pnfs_layout_process() calls pnfs_mark_matching_lsegs_return() on
the on-stack free_me list and jumps to out_forget. Segments whose
reference count drops to zero are unlinked from lo->plh_segs and moved
to free_me by mark_lseg_invalid(); for an idle cached segment the layout
header holds the only reference, so this happens on the first decrement.
out_forget never drains free_me -- only the success path calls
pnfs_free_lseg_list().
Commit 814b849 ("pNFS/NFSv4: Fix a layout segment leak in
pnfs_layout_process()") added the drain; commit 08bd8db
("pNFS/NFSv4: Try to return invalid layout in pnfs_layout_process()")
removed it while switching the destination to lo->plh_return_segs, which
is drained elsewhere. Commit fb700ef ("NFSv4.1: Simplify layout
return in pnfs_layout_process()") switched the destination back to
free_me without restoring the drain.
Restore the pnfs_free_lseg_list() call.
Fixes: fb700ef ("NFSv4.1: Simplify layout return in pnfs_layout_process()")
Reported-by: Yuhao Jiang <[email protected]>
Assisted-by: Claude:claude-opus-5
Cc: [email protected]
Signed-off-by: Junrui Luo <[email protected]>
Signed-off-by: Trond Myklebust <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
fs/nfs/pnfs.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=7c5b0e813efd9124760d5fd1bfc6b229f03fb1a2
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89710 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89710
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:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/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: 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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