[CVE-2026-72035][MODERATE 7.0] net/sched: sch_taprio: Replace direct dequeue call with peek and qdisc_dequeue_peeked

[CVE-2026-72035][MODERATE 7.0] net/sched: sch_taprio: Replace direct dequeue call with peek and qdisc_dequeue_peeked

[AL-KERNEL]

CVE: CVE-2026-72035
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net/sched: sch_taprio: Replace direct dequeue call with peek and qdisc_dequeue_peeked
Commit: 6ee5a7665a9080bcb05d703bf981a579436fd05e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6ee5a7665a9080bcb05d703bf981a579436fd05e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72035
Analysis date: Sat, 15 Aug 2026 10:19:55 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A taprio dequeue ordering bug can orphan a peeked skb in a non-work-conserving child qdisc such as qfq, desynchronize qdisc state, and trigger a NULL pointer dereference kernel panic during ordinary egress traffic when the vulnerable qdisc configuration is present.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-72035 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72035

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
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CVE-2026-72035	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';**CWE-476;*CWE-664;CWE-754;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.3';DESCR 'taprio software dequeue can desynchronize a child qdisc because it peeks an skb but then takes packets through a direct child dequeue path that does not consume the stashed peeked skb. With a non work conserving child such as qfq, this can orphan the peeked skb, corrupt qdisc accounting state, and later re enter an emptied internal list that dereferences NULL in softirq context. For the CVSS the PR:N is used only for the paranoid network adjacent interpretation where the vulnerable taprio and child qdisc configuration already exists and the attacker only needs to cause ordinary egress traffic. The more typical local interpretation is PR:L because a local user or process can generate egress traffic but cannot normally configure qdiscs without CAP_NET_ADMIN. The issue is not a proven memory corruption primitive beyond NULL dereference, so impact is denial of service via kernel panic.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	REMOTE DANGER SIMPLEFIX NETWORK SKB LINUS QDISC PACKET  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. If the vulnerable taprio/qfq configuration already exists, an unprivileged local process can likely trigger the affected egress path by generating ordinary outbound traffic.
* Reliable kernel crash / strong DoS: +1. The commit explicitly describes NULL dereference and kernel panic from softirq.
* Common packet-processing path: +1. This is in the networking qdisc egress path, although not a default qdisc setup.
* Rare AND difficult-to-reach subsystem/configuration: -1. The specific combination requires taprio software path with a non-work-conserving child such as qfq.
* Requires CAP_NET_ADMIN for setup in typical deployments: -1 conservative adjustment. An attacker usually cannot create the vulnerable qdisc hierarchy without administrative network privileges, but exploitation may not require those privileges if the configuration is already present.

Paranoid signals:

* Remote reachable / network-triggerable: +2. In a router, bridge, gateway, or traffic-shaping deployment with the vulnerable qdisc configuration already installed, adjacent or remote-originated traffic may drive ordinary egress.
* Reliable kernel crash / strong DoS: +1. The described failure is a NULL dereference panic in softirq.
* Common packet-processing path: +1. The vulnerable code is in the network scheduler egress datapath.
* Availability impact realistic: +1. Once the vulnerable configuration is present, ordinary traffic can cause a host-wide kernel panic.
* Rare configuration dependency: -1. The taprio plus non-work-conserving child qdisc setup is not a broad default configuration.
* No memory corruption or LPE bonus. The patch supports state desynchronization and NULL dereference, but not UAF, OOB write, type confusion, arbitrary write, or attacker-controlled reclaim.

## 3. Reachability analysis

Typical setup requires CAP_NET_ADMIN to configure taprio and the child qdisc, so a fully unprivileged local user normally cannot create the vulnerable configuration. However, if an administrator or orchestration system already deployed taprio with a non-work-conserving child such as qfq, ordinary egress traffic can reach the buggy path. In forwarding or traffic-shaping deployments, an external or adjacent attacker may be able to induce egress traffic without local code execution, but this depends on the system role and qdisc configuration. The path is not default-enabled on ordinary hosts and should be treated as configuration-dependent networking exposure.

Call-site confidence: high. The patch directly changes the dequeue call in taprio_dequeue_from_txq(), and the commit explains the concrete child qdisc state mismatch and NULL dereference.

## 4. Severity interpretation

This behaves like an actionable Moderate DoS issue rather than an Important memory-corruption vulnerability. The realistic impact is kernel panic through a NULL pointer dereference in the networking softirq path. Theoretical escalation is not supported by the patch because the described primitive is not UAF, overwrite, object replacement, callback corruption, or refcount takeover. It should not be auto-closed without checking whether affected products deploy taprio with qfq or similar non-work-conserving child qdiscs.

## 5. One-sentence report phrase

A taprio dequeue ordering bug can orphan a peeked skb in a non-work-conserving child qdisc such as qfq, desynchronize qdisc state, and trigger a NULL pointer dereference kernel panic during ordinary egress traffic when the vulnerable qdisc configuration is present.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Manual review is required to determine whether the affected product uses taprio software scheduling with qfq or another non-work-conserving child qdisc, and whether untrusted local or network-adjacent traffic can reach the configured egress path.

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

Patch: net/sched: sch_taprio: Replace direct dequeue call with peek and qdisc_dequeue_peeked
Commit: 6ee5a7665a9080bcb05d703bf981a579436fd05e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6ee5a7665a9080bcb05d703bf981a579436fd05e

Commit description:

When taprio's software path peeks a non-work-conserving child qdisc, the
child stashes the peeked skb in its gso_skb; taprio_dequeue_from_txq()
then takes the packet with a direct child ->dequeue() call, which ignores
that stash, orphans the peeked skb and desyncs the child's qlen/backlog.
With a qfq child this re-enters the child on an emptied list and
dereferences NULL, panicking the kernel from softirq on ordinary egress.

Take the packet through qdisc_dequeue_peeked(), as sch_red and sch_sfb
now do. The helper returns the child's stashed skb first and is a no-op
when there is none, so a work-conserving child is unaffected and the
gated path now consumes the skb whose length was charged to the budget.

Fixes: 5a781cc ("tc: Add support for configuring the taprio scheduler")
Cc: stable@vger.kernel.org
Cc: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Reviewed-by: Victor Nogueira <victor@mojatatu.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://patch.msgid.link/20260625-b4-disp-31bcb279-v1-1-85c40b83c529@proton.me
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/sched/sch_taprio.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=6ee5a7665a9080bcb05d703bf981a579436fd05e

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

The original Linux kernel CVE announcement for CVE-2026-72035 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72035

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:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.3

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: 3
  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: NO
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).