[CVE-2026-98381][MODERATE 7.0] veth: manage XDP program pointers during channel resize [ Upstream

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

CVE: CVE-2026-98381
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: veth: manage XDP program pointers during channel resize [ Upstream
Commit: 7a8e143109ff2736dc79e41dcd55af7ceab7520a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7a8e143109ff2736dc79e41dcd55af7ceab7520a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98381
Analysis date: Fri, 09 Oct 2026 22:15:53 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-98381 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98381

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
======================================================================

CVE-2026-98381	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98381 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=MODERATE_KPANIC RESULT=SAME (legacy and Aegis reconciliation agree; 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;CWE-825;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A use after free can occur because removed veth RX queues retain a stale XDP program pointer after channel reduction. If the XDP program is then detached or replaced, bpf_prog_put can release the program while the disabled queues still reference it. A later channel increase can reenable NAPI, and packet processing can execute through the freed program pointer in veth_xdp_rcv_skb, causing a kernel panic and potentially enabling more serious memory corruption. For the CVSS the PR:L reflects that a local user or container process with delegated CAP_NET_ADMIN may be able to resize veth channels and manage the XDP program without having unrestricted host root privileges. The issue is not independently network reachable because packet traffic only activates the stale pointer after the vulnerable state has been prepared locally. Impact is at least a local denial of service via kernel crash and in the worst case may include confidentiality and integrity compromise because the UAF affects a program object used in kernel control flow.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	MAYBE	BPF UAF NETWORK  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK	-	-	checked

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

ActionableScore=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 5
* Raw paranoid score: 5
* Paranoid score: 5
* Conservative floor applied: 4 -> 5 under REAL UAF FLOOR 5 because the actor drives the lifetime transition and the stale object is later consumed in active XDP packet processing rather than cleanup.
* The BPF privileged control-plane exception was checked but does not suppress FLOOR 5 because the stale use occurs after re-enabled NAPI in the active data path, not primarily in cleanup or teardown.
* The BPF conservative cap of 5 is not exceeded.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Conservative signals:

* +2 Real UAF. Removed RX queues retain an XDP program pointer after `bpf_prog_put()` can end the program lifetime.
* +1 Reliable kernel crash. The supplied trace demonstrates a page fault, Oops, and fatal kernel panic during `veth_xdp_rcv_skb()`.
* +1 Attacker-influenced active-object lifetime. A control-plane actor can reduce channels, detach or replace the XDP program, increase channels, and then activate the stale use through packet processing.
* Raw conservative total: 4.
* FLOOR 5 applied because this is a repeatable active-object lifetime transition followed by nontrivial execution-path consumption of the stale program.

Paranoid-only signal:

* +1 Structured stale-object leverage. The stale object is used by the XDP execution path rather than merely inspected or passed to a destructor. This leaves unresolved exploitation relevance around executable program state, although post-free contents are not shown to be controlled.
* Raw paranoid total: 5.

Not awarded:

* No +2 strong exploitation leverage. Controlled reclaim, attacker-shaped replacement contents, callback hijacking from reclaimed data, and arbitrary kernel read or write are not demonstrated.
* No remote-reachability bonus. Network traffic only activates the stale pointer after local control-plane preparation.
* No local-unprivileged bonus. The complete BPF load, XDP attach, channel resize, detach, and trigger sequence is not established for an ordinary user.
* No privilege penalty. Host-admin-equivalent privilege is not positively established, but below-host-admin completion is also unresolved.
* No race penalty. The documented trigger is an ordered state sequence, not a proven narrow or unreliable timing race.
* No separate availability point. The panic is already counted as reliable kernel crash.
* No confidentiality or integrity points. The UAF does not by itself prove disclosure or unauthorized modification.
* No repeated-release/refcount point. There is one `bpf_prog_put()` followed by execution through a stale pointer, not a second put, free, or refcount mutation on the same reference.
* NEW52 B5-R does not apply. No retry-accumulated heap OOB write exists.
* NEW53 B3-PENDING does not apply. No shared-backing write exists.
* NEW54 B4-PENDING does not apply. No authorization decision is changed from DENY to ALLOW.

3. Reachability analysis

The required sequence is channel reduction, XDP detach or replacement, channel increase, and packet reception. Channel management is associated with ethtool and netdevice administration, while XDP program loading and attachment may involve separate CAP_NET_ADMIN, CAP_BPF, CAP_SYS_ADMIN, sysctl, and user-namespace restrictions.

The supplied evidence does not establish whether every required operation is available inside an attacker-created user and network namespace. A veth device being namespace-aware is insufficient to prove that BPF loading and XDP attachment are also available below host-admin privilege. Therefore both `HostAdminRequired` and `NamespaceScopedPrivilege` remain `UNKNOWN`.

No physical hardware is required because veth is virtual. No narrow race is established. Once the vulnerable state is prepared, channel re-enablement and packet delivery provide a direct stale-use path. This is not independently remotely exploitable because a network peer cannot perform the preceding channel and XDP lifecycle operations from traffic alone.

4. Primitive and severity interpretation

The primitive is a concrete use-after-free of an active `struct bpf_prog`. An RX queue removed during channel reduction retains its program pointer. Detaching or replacing the program can drop the final reference through `bpf_prog_put()`. Re-enabling the queue restores NAPI operation without restoring a valid pointer, and subsequent receive processing attempts to run the freed program.

This is active structured stale-object consumption in the normal data path, not fixed stale storage and not a cleanup-only dereference. It is CLASS_B rather than CLASS_A because controlled reclaim, attacker-controlled post-free contents, directed corruption, and useful function-pointer control are not established.

The demonstrated consequence is host kernel panic. A stronger consequence is technically plausible because execution proceeds through a freed program object, but privilege escalation or arbitrary kernel execution is not established. The active execution-path use and attacker-driven lifetime sequence create enough unresolved leverage for `ImportantCandidate=YES`, `ManualReview=REQUIRED`, and `AutoDowngradeAllowed=NO`.

The likely operational severity is Actionable Moderate at minimum. Important classification remains possible after review of BPF privilege scope, allocator reuse, JIT program lifetime, and the exact indirect execution mechanics.

5. One-sentence report phrase

A locally prepared veth channel resize and XDP detach sequence can leave an RX queue referencing a freed BPF program, allowing later packet processing to execute through the stale object and panic the kernel, with stronger exploitation leverage unresolved.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Review the complete namespace and BPF privilege chain, `bpf_prog_put()` retirement semantics, JIT image lifetime, and whether controlled allocation can influence the stale XDP execution path.

7. Call-site confidence

Call-site confidence: high

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

Patch: veth: manage XDP program pointers during channel resize [ Upstream
Commit: 7a8e143109ff2736dc79e41dcd55af7ceab7520a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7a8e143109ff2736dc79e41dcd55af7ceab7520a

Changed files:
  include/linux/filter.h
  include/net/xdp.h
  drivers/net/veth.c
  net/core/dev.c
  kernel/softirq.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=7a8e143109ff2736dc79e41dcd55af7ceab7520a

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

The original Linux kernel CVE announcement for CVE-2026-98381 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98381

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:L/PR:L/UI:N/S:U/C:L/I:L/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: 5

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).