[CVE-2026-68441][MODERATE REGULAR] net/sched: Handle TC_ACT_REDIRECT from qdisc filter chains [ Upstream

[CVE-2026-68441][MODERATE REGULAR] net/sched: Handle TC_ACT_REDIRECT from qdisc filter chains [ Upstream

[AL-KERNEL]

CVE: CVE-2026-68441
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net/sched: Handle TC_ACT_REDIRECT from qdisc filter chains [ Upstream
Commit: c8fd74445e86f88096d2f6cf0f9e4d54d8ed1781
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c8fd74445e86f88096d2f6cf0f9e4d54d8ed1781
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68441
Analysis date: Tue, 11 Aug 2026 21:06:06 -0400
ActionableScore: 4
ActionableScore lower bound: 1
Actionable bucket: Borderline, manual review recommended. Conditional network-triggered DoS, not an Important candidate
Manual review required: YES

Summary:
TC qdisc filter chains returning TC_ACT_REDIRECT can reach bpf_redirect without the required bpf_net_context and trigger a NULL pointer dereference, causing a conditional network-triggered kernel DoS when such filters are deployed.

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

The original Linux kernel CVE announcement for CVE-2026-68441 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68441

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-2026-68441	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-703;CWE-754;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.9';DESCR 'TC qdisc filter chains did not support TC_ACT_REDIRECT returned by a classifier or an eBPF action. After bpf_net_context moved from a per CPU object to task_struct context, a qdisc path that calls bpf_redirect without the required context can hit a NULL pointer dereference in bpf_net_ctx_get_ri and crash the kernel. For the CVSS the PR:N is used in the paranoid network interpretation because a remote sender may only need packet reachability to an already configured qdisc filter path that returns TC_ACT_REDIRECT. The issue is network reachable only in non default deployments where such qdisc filters are installed, so AC:H is used for that interpretation. Impact is denial of service via kernel crash, with no evidence of information disclosure or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended. Conditional network-triggered DoS, not an Important candidate (with actual score 3)	YES	REMOTE NULLPTR BPF SKB HARDWARE QDISC PACKET  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=4
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended. Conditional network-triggered DoS, not an Important candidate**

## 2. Signal breakdown

Paranoid score signals:

* Remote reachable / network-triggerable: +2. If an affected qdisc filter path returning TC_ACT_REDIRECT is already installed, ordinary packets reaching that qdisc path may trigger the crash.
* Reliable kernel crash / strong DoS: +1. The commit explicitly describes a NULL pointer dereference in bpf_net_ctx_get_ri().
* Common networking core path or packet-processing path: +1. The affected code is in TC qdisc packet classification paths under net/sched.
* Availability impact realistic: +1. A reachable packet path can crash the kernel in the affected configuration.
* Rare or non-default runtime condition: -1. Triggering requires a qdisc filter chain returning TC_ACT_REDIRECT, typically through eBPF or act_bpf, which is not a default setup.

Conservative score signals:

* Reliable kernel crash / strong DoS: +1.
* Common networking packet-processing path: +1.
* Availability impact realistic: +1.
* Requires admin/root/CAP_NET_ADMIN/CAP_BPF in typical deployments: -2. Installing the relevant qdisc filter or BPF action normally requires elevated privileges.
* Rare or non-default runtime condition: -1.

Not counted:

* No generic memory corruption bonus. The described primitive is NULL pointer dereference, not UAF, OOB write, type confusion, double free, or arbitrary write.
* No privilege escalation bonus. The patch does not show attacker-controlled reclaim, object replacement, callback control, refcount abuse, or write primitive.
* No confidentiality or integrity impact. The observed impact is crash or packet drop behavior.

## 3. Reachability analysis

In the conservative interpretation, the bug is triggered by a local privileged administrator or process that can configure TC qdisc filters and attach an eBPF or act_bpf action returning TC_ACT_REDIRECT. This normally requires CAP_NET_ADMIN and often BPF-related privileges, especially in products where unprivileged BPF is disabled.

In the paranoid interpretation, once such a filter is already installed, a remote sender may only need packet reachability to the affected qdisc path to trigger the NULL dereference. This makes the crash condition conditionally network-triggerable, but not broadly Internet-exposed by default.

Namespaces and containers matter only if CAP_NET_ADMIN or BPF privileges are delegated inside a container or network namespace. Without such delegation or pre-existing vulnerable configuration, an unprivileged local user should not be able to set up the trigger.

Call-site confidence: high. The patch directly shows qdisc classify callers being converted from tcf_classify() to tcf_classify_qdisc(), and the commit explains the bpf_redirect() crash path.

## 4. Severity interpretation

This behaves like a conditional network-triggered DoS in non-default TC qdisc filter deployments. It is more actionable than a purely local privileged correctness bug because packet traffic may trigger the crash after configuration, but it is not an Important-class issue based on the patch evidence.

Theoretical memory corruption potential is low. The concrete failure mode is NULL pointer dereference in bpf_net_ctx_get_ri(), not a controllable memory corruption primitive. Realistic exploitation evidence supports kernel crash only.

## 5. One-sentence report phrase

TC qdisc filter chains returning TC_ACT_REDIRECT can reach bpf_redirect without the required bpf_net_context and trigger a NULL pointer dereference, causing a conditional network-triggered kernel DoS when such filters are deployed.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because the practical severity depends heavily on deployment: whether qdisc filters returning TC_ACT_REDIRECT are installed, whether untrusted traffic reaches that qdisc path, and whether TC/BPF privileges are delegated to containers or restricted users.

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

Patch: net/sched: Handle TC_ACT_REDIRECT from qdisc filter chains [ Upstream
Commit: c8fd74445e86f88096d2f6cf0f9e4d54d8ed1781
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c8fd74445e86f88096d2f6cf0f9e4d54d8ed1781

Changed files:
  include/net/pkt_cls.h
  net/sched/cls_api.c
  net/sched/sch_cake.c
  net/sched/sch_drr.c
  net/sched/sch_dualpi2.c
  net/sched/sch_ets.c
  net/sched/sch_fq_codel.c
  net/sched/sch_fq_pie.c
  net/sched/sch_hfsc.c
  net/sched/sch_htb.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=c8fd74445e86f88096d2f6cf0f9e4d54d8ed1781

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

The original Linux kernel CVE announcement for CVE-2026-68441 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68441

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:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.9

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: 1
  Paranoid ActionableScore: 4

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).