[CVE-2026-93286][LOW] net: appletalk: fix NULL pointer dereference in aarp_send_ddp()

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

CVE: CVE-2026-93286
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: net: appletalk: fix NULL pointer dereference in aarp_send_ddp()
Commit: 8fc30f0cdf4207a5aa2341c0a98d0f1713b3ce2c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8fc30f0cdf4207a5aa2341c0a98d0f1713b3ce2c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93286
Analysis date: Thu, 24 Sep 2026 21:24:29 -0400
ActionableScore: 2
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-2026-93286 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93286

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-2026-93286	LOW	https://www.kernelcve.org/list/?q=CVE-2026-93286 CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-476;*CWE-20;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A NULL pointer dereference in the AppleTalk LocalTalk transmit path occurs because aarp_send_ddp can use the result of atalk_find_dev_addr without checking whether an AppleTalk interface is configured on the selected device. A local process can reach this path through atalk_sendmsg and sendto when the device has no AppleTalk state, causing an invalid access through at and potentially an Oops or kernel panic. For the CVSS the PR:L value is used because triggering requires a local user process and an AppleTalk socket, but it does not normally require full administrative control once the relevant network configuration exists. The issue is not directly reachable by merely sending packets from a remote host because the vulnerable path is entered through a local transmit operation. The confirmed impact is denial of service. The NULL access does not provide evidence of a UAF, an out of bounds write, an information leak, or a practical privilege escalation primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)  SKIP CVE-2026-93286 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	KASAN NULLPTR SIMPLEFIX SKB HARDWARE LINUS  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2.
* Conservative score: 2.
* Raw paranoid score: 2.
* Paranoid score: 2.
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Local unprivileged trigger. The visible call chain reaches `aarp_send_ddp()` from the ordinary `sendto()` system call, and no capability check is shown for the triggering send operation.
* +1 Reliable kernel crash or strong DoS. Dereferencing `at->s_net` when `atalk_find_dev_addr()` returns NULL produces a confirmed kernel NULL-pointer fault and may cause an Oops or panic depending on system policy.
* No corruption bonus. The established primitive is a low-address invalid read through NULL, not an OOB write, UAF, double release, or active-object corruption.
* No remote-reachability bonus. Remote packets do not directly invoke the vulnerable local transmit path.
* No confidentiality or integrity points. No disclosure, unauthorized modification, or useful memory-corruption primitive is established.
* No strong or weak LPE points. Controlled reclaim, arbitrary write, object replacement, callback influence, and privilege escalation are not demonstrated.
* No additional availability point. It would duplicate the already counted kernel fault.
* No legacy-subsystem penalty. AppleTalk and LocalTalk are uncommon, but the supplied evidence does not fully establish that the required device state is difficult for the evaluated attacker to reach once provisioned.

3. Reachability analysis

A local process can reach the vulnerable path through an AppleTalk socket and `sendto()`. The selected LocalTalk device must lack an associated AppleTalk interface, causing `atalk_find_dev_addr()` to return NULL.

The immediate send operation is below host-admin privilege, so `HostAdminRequired=NO`. Creation or provisioning of the relevant LocalTalk device and routing state may require prior administrative configuration, but that actor is distinct from the process performing the vulnerable send. The supplied evidence does not establish that the complete setup can be created inside an attacker-controlled namespace, so `NamespaceScopedPrivilege=UNKNOWN`.

The issue is not directly network-triggerable. There is no race or special timing requirement. No special physical hardware requirement is established by the supplied patch.

4. Primitive and severity interpretation

The exact primitive is a NULL-pointer dereference at a small offset during local packet transmission. It is neither fixed stale storage nor an active structured-object UAF because no object is freed before use. There is no repeated release, refcount mutation, or post-lifetime operation.

`PrimitiveClass=CLASS_C` because the demonstrated behavior is an invalid read resulting in crash or DoS without an independently useful corruption primitive. The practical consequence is local denial of service. Stronger consequences such as information disclosure, kernel write, or privilege escalation are unsupported.

`ImportantCandidate=NO` because no Important-preserving corruption, ownership, authorization, or boundary-bypass primitive exists. `AutoDowngradeAllowed=YES` because the issue is a constrained NULL dereference with crash-only impact and no unresolved exploitation leverage.

5. One-sentence report phrase

A local process can trigger a NULL pointer dereference in the AppleTalk LocalTalk transmit path by sending through a device without AppleTalk state, causing a kernel Oops or panic without an established confidentiality, integrity, or privilege escalation impact.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch establishes a straightforward NULL dereference and local DoS with no UAF, write primitive, remote trigger, or security-boundary bypass.

7. Call-site confidence

Call-site confidence: high

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

Patch: net: appletalk: fix NULL pointer dereference in aarp_send_ddp()
Commit: 8fc30f0cdf4207a5aa2341c0a98d0f1713b3ce2c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8fc30f0cdf4207a5aa2341c0a98d0f1713b3ce2c

Commit description:

aarp_send_ddp() calls atalk_find_dev_addr(dev) in the LocalTalk fast
path without checking for NULL. When the device has no AppleTalk
interface configured (dev->atalk_ptr == NULL), this leads to a NULL
pointer dereference at the at->s_net access.

 KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
 RIP: 0010:aarp_send_ddp (net/appletalk/aarp.c:552 (discriminator 2))
 Call Trace:
  <TASK>
  atalk_sendmsg (net/appletalk/ddp.c:1715)
  __sys_sendto (net/socket.c:2265 (discriminator 1))
  __x64_sys_sendto (net/socket.c:2272)
  do_syscall_64 (arch/x86/entry/syscall_64.c:94)
  entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)

Add a NULL check consistent with the other callers of
atalk_find_dev_addr().

Fixes: 1da177e ("Linux-2.6.12-rc2")
Reported-by: Xiang Mei <xmei5@asu.edu>
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
Link: https://patch.msgid.link/20260514123806.3085961-3-bestswngs@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/appletalk/aarp.c
  net/appletalk/ddp.c
  net/socket.c
  arch/x86/entry/syscall_64.c
  arch/x86/entry/entry_64.S

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=8fc30f0cdf4207a5aa2341c0a98d0f1713b3ce2c

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

The original Linux kernel CVE announcement for CVE-2026-93286 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93286

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:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: unknown
  Paranoid ActionableScore: 2

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).