[CVE-2026-98775][MODERATE 7.0] nitro_enclaves: fix use-after-free on SLOT_ALLOC failure

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-98775
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: nitro_enclaves: fix use-after-free on SLOT_ALLOC failure
Commit: 466041d14f26dc2babd606a2e85dce08774112a6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=466041d14f26dc2babd606a2e85dce08774112a6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98775
Analysis date: Mon, 19 Oct 2026 04:04:19 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
A failed Nitro Enclaves SLOT_ALLOC request can leave a freed ne_enclave pointer in file private data, allowing deferred file release to perform a cleanup-time use after free that is presently supported as a local kernel fault or denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-98775 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98775

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-98775	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98775 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=MODERATE_KPANIC RESULT=SAME V39_AEGIS_ONE_STEP_UP=MODERATE->MODERATE_KPANIC (final reconciliation agrees; DECISION: both MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A confirmed slab use after free occurs in the Nitro Enclaves SLOT_ALLOC error path because fput() can defer ne_enclave_release() through task work while ne_enclave is freed immediately by the ioctl error handler. The delayed release callback later obtains the stale object through enclave_file private_data and reads ne_enclave slot_uid, which can cause a KASAN report or kernel crash. For the CVSS the PR:L reflects that a local user or service account needs access to the Nitro Enclaves device and permission to invoke the creation ioctl, but full host administrative privileges are not necessarily required. AC:H reflects the requirement to reach a SLOT_ALLOC failure and the relevant deferred release state. The issue is not network reachable. Impact is at least a local denial of service via kernel crash. In the paranoid interpretation, reuse of the freed slab before the delayed callback may expose additional confidentiality or integrity impact and a possible privilege escalation path, so the confirmed UAF requires manual security review. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 3 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE to MODERATE_KPANIC because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. final reconciliation stage MODERATE to MODERATE_KPANIC because the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 4 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	MAYBE	VIRT ERRORPATH UAF LINUS  INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 KPANIC V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=3
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 3
* Raw paranoid score: 3
* Paranoid score: 3
* No floor or cap applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +2 Real UAF. The ioctl error path frees `ne_enclave`, while deferred `__fput()` later invokes `ne_enclave_release()` through the stale `enclave_file->private_data`.
* +1 Realistic kernel fault or DoS. KASAN reliably detects the post-free read on every relevant `SLOT_ALLOC` failure. A fatal KASAN configuration or invalid reclaimed contents can terminate the kernel path.
* No local-unprivileged bonus. Access permissions for the Nitro Enclaves device and complete ioctl sequence are not established.
* No timing penalty. This is an ordered deferred-release error path, not an attacker-dependent narrow race.
* No structured stale-object leverage. The demonstrated stale operation is a cleanup-time read of `slot_uid`. Attacker-controlled reclaim, replacement contents, pointer traversal, callback dispatch, or a subsequent useful operation is not established.
* No repeated-release/refcount signal. The first lifetime-ending operation is the explicit freeing of `ne_enclave`, but the later callback only demonstrates a stale field read. It does not establish a second `put`, `free`, or refcount mutation on the same object.
* No paranoid leverage point. Generic possible slab reuse is insufficient without evidence that meaningful reclaimed fields are consumed.
* No extra availability point. The KASAN fault and possible kernel crash are the same consequence.
* No confidentiality or integrity points. No disclosure, controlled write, protected-state modification, or privilege escalation primitive is demonstrated.
* Controlled reclaim and arbitrary kernel write are not demonstrated.
* Remote reachability is not established.
* `NEW52 B5-R`, `NEW53 B3-PENDING`, V32, V33, and V34 do not apply. There is no OOB write, shared-backing write, checksum corruption, or downstream trust-boundary consumer.
* `B4-PENDING` does not apply because no authorization decision changes from DENY to ALLOW.
* FLOOR 5 was not applied because this is a cleanup callback UAF without a concrete repeated lifetime mutation or meaningful post-reuse processing.

3. Reachability analysis

The trigger is a local `ne_create_vm_ioctl()` operation against the Nitro Enclaves device followed by a failed `SLOT_ALLOC` request. The supplied evidence does not establish whether an ordinary user, a delegated service account, or only an administrator can access the relevant device node and complete this operation. Therefore, `HostAdminRequired` and `RequiresHostUID0` remain `UNKNOWN`.

No namespace-scoped capability path is shown. Nitro Enclaves support and suitable AWS Nitro hardware or virtual device exposure are prerequisites. The bug is not remotely network-triggerable.

The vulnerable ordering is deterministic once `SLOT_ALLOC` fails in a context where `fput()` defers final release through task work. It should not be scored as a hard race, although reliably inducing the allocation failure may depend on device state or resource availability.

4. Primitive and severity interpretation

The exact primitive is a confirmed slab use-after-free read. `enclave_file->private_data` retains a pointer to the freed `ne_enclave`, and `ne_enclave_release()` later dereferences `slot_uid`.

`ne_enclave` is an active structured object, but the demonstrated stale use is confined to deferred error cleanup. The evidence does not establish controlled replacement, repeated lifetime mutation, callback control, arbitrary read or write, disclosure, or a security-boundary bypass.

This is category A from the cleanup distinction: an ordinary stale cleanup dereference. It is not category B repeated lifetime corruption because the callback is not shown performing a second release or refcount mutation through the freed object.

`CLASS_B` is appropriate because the UAF is real. `ImportantCandidate=NO` is appropriate because meaningful exploitation leverage beyond fault or DoS is not established. `AutoDowngradeAllowed=YES` reflects that this is presently a constrained cleanup UAF, although manual review remains recommended to confirm device permissions and the complete behavior of `ne_enclave_release()` when reclaimed memory makes `slot_uid` nonzero.

Likely operational severity is Moderate or lower, dependent on access to the Nitro Enclaves device and the ability to induce `SLOT_ALLOC` failure.

5. One-sentence report phrase

A failed Nitro Enclaves SLOT_ALLOC request can leave a freed ne_enclave pointer in file private data, allowing deferred file release to perform a cleanup-time use after free that is presently supported as a local kernel fault or denial of service.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm device-node permissions, reliable control over `SLOT_ALLOC` failure, and whether a nonzero reclaimed `slot_uid` causes deeper stale-object processing beyond the demonstrated read.

7. Call-site confidence

Call-site confidence: high

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

Patch: nitro_enclaves: fix use-after-free on SLOT_ALLOC failure
Commit: 466041d14f26dc2babd606a2e85dce08774112a6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=466041d14f26dc2babd606a2e85dce08774112a6

Commit description:

When ne_create_vm_ioctl() fails the SLOT_ALLOC request after
anon_inode_getfile() has succeeded, the error path calls
fput(enclave_file) and then frees ne_enclave.

In normal userspace context, fput() defers the final __fput() via
task_work. ne_enclave_release() therefore runs after ne_enclave has
already been freed and dereferences ne_enclave->slot_uid, causing a
use-after-free: KASAN: slab-use-after-free in ne_enclave_release.

The enclave has no slot allocated and is not yet linked into the
enclaves list on this error path, so ne_enclave_release() is expected
to return early when slot_uid is zero. However, reading slot_uid
already accesses the freed object.

Clear enclave_file->private_data before fput() on the error path.
ne_enclave_release() then returns immediately when private_data is
NULL, leaving the ioctl error path as the sole owner of ne_enclave.
This is safe because the file has not been fd_install()'d yet.

Tested on an AWS EC2 m5.2xlarge with CONFIG_KASAN=y. Without the
patch, the reproducer triggers a KASAN slab-use-after-free on every
SLOT_ALLOC failure. With the patch, no KASAN report is produced and
the SLOT_ALLOC error is still returned. Normal enclave creation and
teardown are unaffected.

Fixes: 9c8eb50 ("nitro_enclaves: Add logic for terminating an enclave")
Cc: stable@vger.kernel.org
Co-developed-by: Zhaofeng Chen <zhaofeng.chen@certik.com>
Signed-off-by: Zhaofeng Chen <zhaofeng.chen@certik.com>
Signed-off-by: Yuxiao Wang <yuxiao.wang@certik.com>
Reviewed-by: Alexander Graf <graf@amazon.com>
Link: https://patch.msgid.link/20260909124400.27857-1-graf@amazon.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/virt/nitro_enclaves/ne_misc_dev.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=466041d14f26dc2babd606a2e85dce08774112a6

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

The original Linux kernel CVE announcement for CVE-2026-98775 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98775

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