[CVE-2026-89784][LOW] SUNRPC: check rpc_sockaddr2uaddr() return value in rpcb_register_inet4/6 [ Upstream

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

CVE: CVE-2026-89784
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: SUNRPC: check rpc_sockaddr2uaddr() return value in rpcb_register_inet4/6 [ Upstream
Commit: 04441b792ec40eb66349b5fab34b6a2090b5b2dd
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=04441b792ec40eb66349b5fab34b6a2090b5b2dd
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89784
Analysis date: Wed, 16 Sep 2026 05:01:49 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89784 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89784

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: LOW
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-89784	LOW	https://www.kernelcve.org/list/?q=CVE-2026-89784 CHECK WITH IMPACT FROM ORIG NN LOW	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-252;**CWE-476;CWE-703;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'A NULL pointer dereference in the SUNRPC rpcbind registration path can occur because rpcb_register_inet4 and rpcb_register_inet6 store the result of rpc_sockaddr2uaddr without checking for allocation failure. If the small GFP_KERNEL kstrdup inside rpc_sockaddr2uaddr returns NULL under memory pressure, the NULL address string can reach encode_rpcb_string and strlen can oops the kernel during synchronous RPCBPROC_SET encoding. For the CVSS the PR:L in the paranoid score reflects a local user or process that can create strong memory pressure while an RPC service registration is triggered, although direct service registration is normally administrative. The issue is not directly network reachable because the failing path is local kernel service registration with local rpcbind rather than handling remote RPC traffic. Impact is denial of service via kernel oops or crash. No direct confidentiality or integrity impact is supported because the primitive is a NULL pointer dereference rather than UAF, OOB access, or arbitrary write.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	YES	REMOTE KASAN OOB NULLPTR NOMEMCHK NETWORK KERNEL_PANIC_PLUS_UAF LINUS  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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

ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap changed the score.

2. Signal breakdown

Positive signals:

* +1 Reliable kernel crash / strong DoS: the unchecked NULL from rpc_sockaddr2uaddr() can reach encode_rpcb_string(), where strlen(NULL) causes an Oops or kernel crash.

Negative or non-awarded signals:

* +0 Real UAF: not awarded. The patch establishes NULL pointer dereference, not use-after-free or stale lifetime use.
* +0 Concrete repeated release/refcount: not awarded. No first release, surviving dangling reference, or second lifetime mutation is present.
* +0 Controlled reclaim / arbitrary write: not demonstrated.
* +0 Confidentiality / integrity: not awarded. The primitive is NULL dereference in strlen(), not disclosure, OOB access, UAF, or write corruption.
* +0 Remote reachability: not awarded. The failing path is local RPC service registration with local rpcbind, not remote RPC packet processing.
* +0 Local unprivileged trigger: not awarded. A local user may contribute memory pressure, but the complete trigger also requires RPC service registration, which is not established as below host admin.
* +0 Extra availability: not awarded because the same Oops/crash is already counted once.
* +0 Race/timing penalty: not applied. This is an allocation failure/error handling bug, not a timing race.
* +0 Host-admin penalty: not applied because host-admin-equivalent privilege is likely for the shown nfsd control path, but the complete privilege boundary across nfsd, lockd, and nfs-callback is not fully resolved from supplied evidence.

3. Reachability analysis

The directly shown call path goes through nfsctl_transaction_write(), write_ports(), svc_addsock(), svc_setup_socket(), svc_register(), nfsd_rpcbind_set(), and then rpcbind registration. That path is normally administrative for nfsd service setup.

The bug requires rpc_sockaddr2uaddr() to fail its final GFP_KERNEL kstrdup(), so practical triggering also requires memory pressure or fault injection. A local unprivileged process may be able to create memory pressure, but supplied evidence does not show that the same low-privileged actor can also initiate the required in-kernel RPC service registration.

No network-triggerable packet-processing path is established. The RPCBPROC_SET encoding is sent during local kernel service registration with local rpcbind, not as a direct response to attacker-controlled remote traffic.

No namespace-scoped complete trigger chain is established. No special hardware, boot option, or rare device prerequisite is indicated.

4. Primitive and severity interpretation

The exact primitive is unchecked allocation failure leading to NULL pointer dereference. rpcb_register_inet4() and rpcb_register_inet6() assign map->r_addr from rpc_sockaddr2uaddr() without checking for NULL. The NULL is later consumed as a string by encode_rpcb_string(), whose strlen(string) dereferences it.

This is CLASS_C because the demonstrated behavior is crash/DoS from invalid state. It is not Class B because there is no real lifetime violation, UAF, RCU stale object, repeated put/free/refcount mutation, or post-lifetime object use. It is not Class A because there is no controlled corruption, authorization bypass, semantic reinterpretation, COW violation, protected resource access, or LPE evidence.

Demonstrated consequence is kernel Oops/crash. Speculative consequences beyond DoS are not supported by the patch or supplied context. ImportantCandidate=NO because the primitive is a constrained NULL dereference with no meaningful unresolved exploitation leverage. AutoDowngradeAllowed=YES because no concrete corruption, boundary bypass, or lifetime primitive would be lost by treating this as ordinary Moderate/Low-like triage.

5. One-sentence report phrase

A missing NULL check in SUNRPC rpcbind registration can pass a failed rpc_sockaddr2uaddr allocation into encode_rpcb_string(), causing strlen(NULL) and a local kernel crash under memory pressure during RPC service registration.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: this is a NULL pointer dereference DoS in an allocation failure path, with no UAF, no memory corruption primitive, no direct network reachability, and no supported confidentiality, integrity, or privilege escalation impact.

7. Call-site confidence

Call-site confidence: high

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

Patch: SUNRPC: check rpc_sockaddr2uaddr() return value in rpcb_register_inet4/6 [ Upstream
Commit: 04441b792ec40eb66349b5fab34b6a2090b5b2dd
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=04441b792ec40eb66349b5fab34b6a2090b5b2dd

Changed files:
  lib/string.c
  net/sunrpc/rpcb_clnt.c
  net/sunrpc/auth.c
  net/sunrpc/clnt.c
  net/sunrpc/sched.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=04441b792ec40eb66349b5fab34b6a2090b5b2dd

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

The original Linux kernel CVE announcement for CVE-2026-89784 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89784

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:H/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: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: unknown
  Paranoid ActionableScore: 1

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).