[CVE-2026-90115][MODERATE REGULAR] xsk: fix NULL pointer dereference in __xsk_rcv() [ Upstream

[CVE-2026-90115][MODERATE REGULAR] xsk: fix NULL pointer dereference in __xsk_rcv() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-90115
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: xsk: fix NULL pointer dereference in __xsk_rcv() [ Upstream
Commit: aaebce297efc3e3dccb98a6ff838cfaa47db08db
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=aaebce297efc3e3dccb98a6ff838cfaa47db08db
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90115
Analysis date: Thu, 17 Sep 2026 23:16:41 -0400
ActionableScore: 3
ActionableScore lower bound: 2
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-2026-90115 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90115

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-2026-90115	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90115 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-690;CWE-252;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 AF_XDP multi-buffer receive path can occur because __xsk_rcv() calls xsk_buff_alloc() in a loop without checking whether it returned NULL. xsk_buff_can_alloc() only counts fill queue entries and does not validate their addresses, so allocation can fail after the precheck while the code still dereferences the returned pointer. A local user or local service with access to AF_XDP setup can trigger the vulnerable state by providing fill queue entries that are counted but later rejected, with packet reception driving execution into the Rx path. For the CVSS the PR:L is used because reliable triggering requires local code execution or a local process context with AF_XDP access, not merely remote packet delivery. The issue is not directly Internet reachable, although incoming traffic can be part of the trigger after local AF_XDP configuration. Impact is denial of service via kernel crash only.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	YES	KASAN OOB NULLPTR INIT NOMEMCHK SKB PACKET  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	YES	NO	checked

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

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2. No floor or cap applied.
* Raw paranoid score: 3
* Paranoid score: 3. No floor or cap applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Positive conservative signals:

* +1 Reliable kernel crash / strong DoS. The supplied trace shows a general protection fault and KASAN NULL pointer dereference in `__xsk_rcv()`.
* +1 Attacker-influenced invalid AF_XDP queue state. The failure depends on fill queue entries that are counted by `xsk_buff_can_alloc()` but later rejected by `xsk_buff_alloc()`, causing a NULL return to be dereferenced.

Additional paranoid signal:

* +1 Packet receive path exposure after AF_XDP setup. Incoming packets can drive execution into the vulnerable Rx path once the local AF_XDP/XDP configuration exists, but this is not direct remote reachability by itself.

Non-awarded signals:

* Remote reachable / directly network-triggerable +2 not awarded. Remote packets participate only after local AF_XDP setup and queue state control.
* Local unprivileged trigger +1 not awarded. The complete AF_XDP/XDP setup privilege boundary is not established as ordinary unprivileged.
* Strong LPE / strong exploitation leverage +2 not awarded. No controlled reclaim, arbitrary write, callback control, or privilege escalation primitive is shown.
* Real UAF +2 not awarded. This is an unchecked NULL return dereference, not stale post-lifetime object use.
* C/I impact not awarded. The evidence supports crash/DoS only.
* Extra availability point not awarded. The demonstrated availability impact is the same kernel crash already counted.
* BPF/XDP privilege-gating reviewed. No floor 5 is applied because this is not a UAF and no stronger corruption primitive is established.

3. Reachability analysis

The vulnerable path is in AF_XDP multi-buffer receive handling. A local process or local service with AF_XDP access can influence the UMEM/fill queue state so that `xsk_buff_can_alloc()` succeeds while later `xsk_buff_alloc()` returns NULL.

The exact privilege boundary is unresolved from the supplied patch alone. AF_XDP/XDP usage may involve BPF program loading, XDP attachment, netdevice control, and socket/UMEM setup, which may require capabilities such as CAP_BPF, CAP_NET_ADMIN, CAP_NET_RAW, or prior privileged setup depending on kernel configuration and deployment. Therefore `HostAdminRequired=UNKNOWN`.

Namespace-scoped privilege is also unresolved. The input does not establish that all required stages, including XDP/BPF setup and AF_XDP operation, can be completed inside attacker-created namespaces below host admin. Therefore `NamespaceScopedPrivilege=UNKNOWN`.

This is not directly Internet reachable. Network traffic can help drive the receive path only after the vulnerable AF_XDP setup exists. No special physical hardware requirement is established beyond an AF_XDP-capable networking setup. No race is involved.

4. Primitive and severity interpretation

The exact primitive is an unchecked allocation failure leading to NULL pointer dereference. `xsk_buff_alloc()` may return NULL after the earlier availability check, and the old code then used `xsk_xdp->data`, causing a fault.

This is not an active structured-object UAF and not fixed stale storage. It is a Class C invalid-state / NULL-dereference crash. There is no concrete repeated release/refcount operation. There is no evidence that a first lifetime operation can free an object followed by a second lifetime mutation on the same dangling reference.

Demonstrated consequence is local or locally configured DoS via kernel crash. Speculative consequences beyond DoS are not supported by the patch. There is no shown controlled reclaim, arbitrary read/write, information disclosure, privilege escalation, or authorization bypass.

`ImportantCandidate=NO` because the established primitive is crash-only and lacks unresolved meaningful corruption leverage. `AutoDowngradeAllowed=YES` because this is a constrained Class C DoS issue without a real UAF, security-boundary bypass, or strong corruption primitive.

Likely operational severity is ordinary-to-borderline Moderate depending on whether untrusted local users or services can configure AF_XDP on the affected system.

5. One-sentence report phrase

A NULL pointer dereference in the AF_XDP multi-buffer receive path can let a local process with AF_XDP control crash the kernel by causing `xsk_buff_alloc()` to fail after the fill queue precheck succeeds.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the demonstrated primitive is DoS-only, but it sits in a network receive path and the practical risk depends on the local AF_XDP/XDP privilege model in the evaluated product.

7. Call-site confidence

Call-site confidence: high

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

Patch: xsk: fix NULL pointer dereference in __xsk_rcv() [ Upstream
Commit: aaebce297efc3e3dccb98a6ff838cfaa47db08db
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=aaebce297efc3e3dccb98a6ff838cfaa47db08db

Changed files:
  net/xdp/xsk.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=aaebce297efc3e3dccb98a6ff838cfaa47db08db

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

The original Linux kernel CVE announcement for CVE-2026-90115 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90115

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: 2
  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).