[CVE-2026-89544][MODERATE REGULAR] SUNRPC: fix gssx_dec_option_array error path bugs [ Upstream

[CVE-2026-89544][MODERATE REGULAR] SUNRPC: fix gssx_dec_option_array error path bugs [ Upstream

[AL-KERNEL]

CVE: CVE-2026-89544
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: SUNRPC: fix gssx_dec_option_array error path bugs [ Upstream
Commit: 3ff45361e9469e85c0f86b8e7b82c63e50bab8ef
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3ff45361e9469e85c0f86b8e7b82c63e50bab8ef
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89544
Analysis date: Sat, 12 Sep 2026 03:43:00 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
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-2026-89544 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89544

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-2026-89544	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89544 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';**CWE-476;*CWE-401;*CWE-416;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A NULL-pointer dereference can occur in the SUNRPC GSS upcall decode path because gssx_dec_option_array() could return an error with options count set to 1 while options data is NULL. The caller may then trust the nonzero count and dereference options data during gssp_accept_sec_context_upcall(), causing a kernel crash. The same error path also leaked a decoded group_info reference, and the cleanup logic around group_info had a latent use-after-free risk if the leak was fixed without clearing the pointer. For the CVSS the PR:L value is used for the paranoid score because a local user or local process may be able to trigger GSS upcall handling or memory pressure on systems using SUNRPC GSS, while direct control of the malformed XDR reply normally depends on the local gssproxy service. The issue is not directly network reachable in the same way as a TCP parser bug, but remote RPCSEC_GSS clients may indirectly exercise this path on configured NFS or SUNRPC servers. Impact is at least local denial of service via kernel crash, with limited confidentiality or integrity impact kept for manual review because the patch context includes refcounted cleanup and a UAF candidate.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	YES	REMOTE INIT LEAK ERRORPATH UAF NETWORK  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	YES	NO	checked

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

ActionableScore=3
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 3
* Raw paranoid score: 3
* Paranoid score: 3
* Final recommended bucket: **Borderline / manual review recommended**::

No floor or cap changed the score.

2. Signal breakdown

Positive signals:

* +1 Weak invalid-state / structured consistency bug. `oa->count` could remain 1 while `oa->data` is NULL, and the caller trusted the count.
* +1 Reliable kernel crash / strong DoS. The supplied call path shows `res.options.data[0].value` can be dereferenced when `data` is NULL.
* +1 Concrete persistent kernel resource/reference leak. `cr_group_info` is refcounted and kvmalloc backed, but the old error path used bare `kfree(creds)` and could lose the reference instead of using `put_group_info()`.

Non-awarded material signals:

* RealUAF not awarded. The described UAF is latent in the sense that a naive leak fix using `free_svc_cred()` would expose it. The vulnerable pre-patch flow shown here does not concretely perform the second `put_group_info()` on the already freed `cr_group_info`.
* Concrete repeated release/refcount +1 not awarded. The first release via `groups_free()` and the later `put_group_info()` are not both present as a concrete reachable pre-patch sequence in the supplied diff.
* Paranoid repeated-refcount leverage +1 not awarded. The second stale lifetime mutation is prevented by this patch and is described as a latent hazard, not an established current primitive.
* C/I not awarded. No disclosure, arbitrary write, controlled reclaim, credential modification, or protected resource access is established.
* Remote reachable +2 not awarded. Remote RPCSEC_GSS clients may indirectly exercise SUNRPC GSS paths, but direct attacker control of the malformed XDR response normally depends on local upcall/gssproxy behavior.
* Extra Availability not awarded. The same NULL dereference crash is already counted once.
* ImportantCandidate not set. The established current impact is NULL dereference plus resource leak, not a concrete active UAF or repeated refcount mutation.

Repeated release/refcount checklist:

* First release can end lifetime: potentially yes for `groups_free()` / group storage, but this is on the old inner error path.
* Exact same reference survives: yes, the old code did not clear `creds->cr_group_info`.
* Second operation is a real lifetime/refcount mutation: only in the hypothetical or newly wired cleanup path using `free_svc_cred()`, not established as a current pre-patch reachable second operation.
* Dedicated +1 awarded: no.
* Paranoid repeated-refcount +1 awarded: no.
* FLOOR 5 applied: no.

3. Reachability analysis

The vulnerable code is in the SUNRPC GSS XDR decode path used by GSS upcall handling. A local process may be able to trigger GSS authentication/upcall activity on systems using NFS or SUNRPC with RPCSEC_GSS, and memory pressure may help reach allocation-failure paths. However, the complete path to attacker-controlled malformed XDR data is not proven for an ordinary local user because the response normally comes from a local GSS upcall component such as gssproxy or rpc.gssd.

Host-admin-equivalent privilege is not positively established as required for every trigger, so `HostAdminRequired=UNKNOWN` rather than YES. Below-host-admin reachability is also not fully established, so no local unprivileged bonus is awarded. No namespace-scoped capability path is shown. No special hardware, boot mode, or race timing is required. This is an error-path and allocation/decoder consistency issue, not a timing race.

4. Primitive and severity interpretation

The established primitive is an inconsistent decoded option-array state leading to NULL pointer dereference in the caller, plus a concrete refcounted `group_info` leak. The object is structured kernel state, but the demonstrated stale behavior is not a current concrete UAF in the supplied pre-patch flow. The UAF described by the commit is a latent cleanup hazard that would appear if the leak were fixed by calling `free_svc_cred()` without also changing `out_free_groups`.

This is therefore closer to Class C crash/DoS and resource-management behavior than Class B active lifetime corruption. The demonstrated consequence is kernel crash and resource leak. The speculative consequence is that related refcount cleanup mistakes could become a UAF if fixed incorrectly, which justifies manual review but not Important-grade scoring by itself.

`ImportantCandidate=NO` because no concrete active UAF, controlled reclaim, repeated refcount mutation, arbitrary write, disclosure, or boundary bypass is established. `AutoDowngradeAllowed=YES` because the current demonstrated primitive is constrained to DoS/resource leak and does not leave a meaningful unresolved Class B exploitation primitive.

5. One-sentence report phrase

A SUNRPC GSS XDR option-array decoder error path can leave count and data inconsistent, causing a NULL pointer dereference in the caller, while a related credential cleanup bug leaks refcounted group_info state and should be manually reviewed for cleanup correctness.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because the patch touches refcounted credential cleanup and explicitly prevents a latent UAF-style cleanup hazard, even though the supplied pre-patch control flow establishes NULL dereference and resource leak rather than a current concrete UAF.

7. Call-site confidence

Call-site confidence: medium

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

Patch: SUNRPC: fix gssx_dec_option_array error path bugs [ Upstream
Commit: 3ff45361e9469e85c0f86b8e7b82c63e50bab8ef
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3ff45361e9469e85c0f86b8e7b82c63e50bab8ef

Changed files:
  net/sunrpc/auth_gss/gss_rpc_xdr.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=3ff45361e9469e85c0f86b8e7b82c63e50bab8ef

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

The original Linux kernel CVE announcement for CVE-2026-89544 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89544

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:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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