[CVE-2026-89703][MODERATE 7.0] nfsd: set SC_STATUS_FREED in nfsd4_drop_revoked_stid for delegations

[CVE-2026-89703][MODERATE 7.0] nfsd: set SC_STATUS_FREED in nfsd4_drop_revoked_stid for delegations

[AL-KERNEL]

CVE: CVE-2026-89703
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: nfsd: set SC_STATUS_FREED in nfsd4_drop_revoked_stid for delegations
Commit: d832a0587528853d45481d1faf75d4b5d062adaf
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d832a0587528853d45481d1faf75d4b5d062adaf
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89703
Analysis date: Sat, 12 Sep 2026 05:46:58 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-89703 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89703

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-2026-89703	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89703 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'A use-after-free can occur in the NFS server state handling path because nfsd4_drop_revoked_stid releases an admin revoked delegation without marking the stateid as freed. A concurrent revoke_delegation path can then treat the same delegation as not yet processed and add the already freed object to the cl_revoked list. Later traversal of cl_revoked in client teardown can dereference freed memory and crash the kernel. For the CVSS the PR:L is selected because reliable triggering normally requires an NFSv4 client context with access to the affected export or session, not local root on the victim. The issue is network reachable through the NFS server control and state protocol paths, but exploitation requires a specific revoked delegation and FREE_STATEID timing window. Impact is at least denial of service via kernel crash. For the paranoid score, the UAF and list corruption primitive justify C:H/I:H/A:H for manual review sensitivity, even though a stable privilege escalation path is not proven by the patch text alone.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6)	YES	DANGER DISK INIT RACE UAF NETWORK KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 5
* Applied conservative floor/cap: Real UAF floor 5 applied because a freed active NFS delegation can be reinserted into cl_revoked and later traversed, leaving unresolved post-lifetime list/object corruption.
* Raw paranoid score: 6
* Paranoid score: 6
* Applied paranoid floor/cap: none.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Conservative signals:

* +2 Real UAF / active lifetime violation. The commit explicitly states that a freed delegation is added to cl_revoked and later traversal in __destroy_client produces use-after-free.
* +2 Network-reachable protocol path. The vulnerable state operation is in nfsd/NFSv4 server handling and can be influenced through NFSv4 state protocol operations such as FREE_STATEID, assuming an attacker has the required NFS client context.
* +1 Reliable kernel crash / strong DoS. Traversal of cl_revoked containing a freed delegation can dereference freed memory and crash the kernel.
* -1 Hard timing/state prerequisite. The demonstrated path requires an admin-revoked delegation and interaction with revoke_delegation/FREE_STATEID timing, so conservative scoring treats this as a constrained race/state window.

Paranoid signals:

* +2 Real UAF / active lifetime violation. Same as conservative.
* +2 Network-reachable protocol path. Same as conservative.
* +1 Reliable kernel crash / strong DoS. Same as conservative.
* +1 Active post-free list/object corruption concern. The freed delegation is not merely read once. It can be inserted into cl_revoked via list_add and later processed as a live list element, leaving meaningful unresolved Class B exploitation leverage.

Important non-awarded signals:

* Controlled reclaim is not demonstrated.
* Arbitrary kernel read/write is not demonstrated.
* Privilege escalation is not demonstrated.
* Confidentiality and integrity points are not awarded as established consequences.
* Concrete repeated release/refcount signal is not awarded. The patch establishes post-free list insertion/traversal, but not a visible second put/release/refcount mutation on the exact same dangling reference.
* Extra Availability is not awarded because the same kernel crash is already counted.
* CLASS_A is not used because there is no demonstrated controlled reclaim, directed write, callback hijack, or LPE.

Repeated-release/refcount checklist:

* First release can end lifetime: yes, nfs4_put_stid can drop the stateid/delegation lifetime.
* Exact same reference survives to a second lifetime/refcount mutation: not established from supplied patch text.
* Second operation is a real lifetime/refcount mutation: not established.
* +1 Concrete repeated release/refcount awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: yes, but due active post-free list/object corruption and traversal, not due repeated refcount.

3. Reachability analysis

The evaluated attacker is best modeled as a remote NFSv4 client with access to the relevant export/session and ability to exercise NFSv4 state operations. The issue is not a raw unauthenticated packet parser bug, because reliable triggering appears to require a valid NFSv4 state context and an admin-revoked delegation state.

Host-admin-equivalent privilege is not positively established as required for the whole vulnerable sequence, but the supplied text also does not fully prove that an ordinary remote client alone can create the complete admin-revoked delegation condition. Therefore HostAdminRequired is UNKNOWN rather than YES or NO.

Namespace-scoped privilege is not relevant from the supplied evidence. No complete namespace-scoped trigger chain is established.

Prior NFS server configuration and exported filesystem availability are deployment prerequisites, but those are normal service exposure conditions rather than attacker-created setup. No special hardware is required.

Race repeatability is uncertain. The bug involves interaction between FREE_STATEID processing and revoke_delegation state handling. Conservative scoring treats the timing/state condition as constrained, while paranoid scoring does not assume it is a one-shot or practically unreachable race.

4. Primitive and severity interpretation

The exact primitive is a real use-after-free in NFS server state handling. nfsd4_drop_revoked_stid releases an admin-revoked delegation without setting SC_STATUS_FREED. revoke_delegation can then fail to recognize that FREE_STATEID already processed the delegation and can add the already freed delegation to cl_revoked. Later __destroy_client traversal can consume the stale list element.

This is an active structured object UAF rather than fixed stale storage. The stale object is an NFS delegation/stateid object participating in client state lists. The demonstrated consequence is kernel crash/DoS. The speculative consequence is stronger memory corruption or privilege impact from post-free list/object reuse, but that is not proven by the supplied patch.

This is not merely an ordinary stale cleanup dereference. The stronger concern is that the freed delegation can be linked into an active revoked-delegation list and later treated as live state. However, the evidence still falls short of CLASS_A because controlled reclaim, attacker-shaped replacement contents, arbitrary write, callback control, and demonstrated LPE are absent.

PrimitiveClass is CLASS_B. ImportantCandidate is YES because a network-reachable active-object UAF with post-free list corruption should not be automatically treated as ordinary crash-only Moderate. AutoDowngradeAllowed is NO because meaningful unresolved lifetime/list corruption leverage would be lost by automatic downgrade.

Likely operational severity is Actionable Moderate at minimum, with Strong Important review warranted if further analysis shows that an NFS client can reliably create the revoked-delegation timing and influence post-free reuse.

5. One-sentence report phrase

A network-reachable NFSv4 server state-handling UAF can occur when an admin-revoked delegation is freed without SC_STATUS_FREED, allowing it to be re-added to cl_revoked and later traversed as live state, causing at least kernel DoS and requiring manual review for unresolved post-free list corruption leverage.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch explicitly establishes a real kernel UAF in nfsd involving a freed active delegation object being added to a live list and later traversed. Controlled exploitation is not proven, but the primitive is stronger than a simple NULL dereference or resource leak.

7. Call-site confidence

Call-site confidence: medium

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: nfsd: set SC_STATUS_FREED in nfsd4_drop_revoked_stid for delegations
Commit: d832a0587528853d45481d1faf75d4b5d062adaf
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d832a0587528853d45481d1faf75d4b5d062adaf

Commit description:

nfsd4_drop_revoked_stid() handles FREE_STATEID for admin-revoked
delegations but does not set SC_STATUS_FREED before releasing cl_lock.
revoke_delegation() uses this flag to detect whether FREE_STATEID has
already processed the delegation -- without it, the freed delegation is
added to cl_revoked via list_add(), producing a use-after-free when
cl_revoked is later traversed in __destroy_client().

The SC_STATUS_REVOKED path in nfsd4_free_stateid() (line 7983) already
sets SC_STATUS_FREED correctly. Apply the same pattern to the
SC_STATUS_ADMIN_REVOKED path in nfsd4_drop_revoked_stid().

Fixes: 8dd91e8 ("nfsd: fix race between laundromat and free_stateid")
Cc: stable@vger.kernel.org
Signed-off-by: Zhenghang Xiao <kipreyyy@gmail.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260526104554.46262-1-kipreyyy@gmail.com
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/nfsd/nfs4state.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=d832a0587528853d45481d1faf75d4b5d062adaf

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-89703 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89703

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:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.5

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: 5
  Paranoid ActionableScore: 6

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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).