[CVE-2026-45845][MODERATE REGULAR] net/sched: taprio: fix NULL pointer dereference in class dump [ Upstream

[CVE-2026-45845][MODERATE REGULAR] net/sched: taprio: fix NULL pointer dereference in class dump [ Upstream

[AL-KERNEL]

CVE: CVE-2026-45845
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net/sched: taprio: fix NULL pointer dereference in class dump [ Upstream
Commit: ec2501e361b08b50bcb1e7b3253fc861abbda28d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ec2501e361b08b50bcb1e7b3253fc861abbda28d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45845
Analysis date: Wed, 27 May 2026 08:22:58 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A local TAPRIO qdisc control-plane sequence can leave a NULL child qdisc slot and later trigger a NULL pointer dereference during RTM_GETTCLASS class dump, causing a kernel panic on systems where TAPRIO and namespace-scoped CAP_NET_ADMIN are available.

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

The original Linux kernel CVE announcement for CVE-2026-45845 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45845

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-2026-45845	MODERATE	CHECK	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-754;CWE-703;BEST CVSS score: '5.5';DESCR 'A NULL pointer dereference in the TAPRIO class dump path can occur after a child qdisc is deleted and q qdiscs contains a NULL slot. A later RTM_GETTCLASS dump can walk the TAPRIO classes and dereference the missing child qdisc, causing a kernel panic. For the CVSS the PR:L is used because namespace scoped CAP_NET_ADMIN is enough, and on systems with unprivileged user namespaces a local user may create a network namespace and configure TAPRIO there. The issue is not directly network reachable because it is triggered through rtnetlink qdisc control plane operations rather than packet processing. Impact is denial of service only. No UAF, double free, arbitrary write, or privilege escalation primitive is shown by this patch.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 4)  SKIP CVE-2026-45845  SKIP The Fixes patch not applied yet, so unlikely that actual: 665338b2a7a0139337d1f85be65ed16e487f84c1 YES  NO NO unknown 	MAYBE	REMOTE KASAN OOB NULLPTR NETWORK LINUS TEST QDISC PACKET  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

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

ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

* Local unprivileged trigger: +1
  On systems with unprivileged user namespaces enabled, a local user can create a network namespace, obtain namespace-scoped `CAP_NET_ADMIN`, configure TAPRIO, delete a child qdisc, and trigger the class dump.

* Local high-control netlink control-plane API: +1
  The trigger uses rtnetlink qdisc and class operations, where the local caller controls qdisc setup, grafting, deletion, and dump sequencing.

* Reliable kernel crash / strong DoS: +1
  The commit includes a concrete NULL pointer dereference call trace in `taprio_dump_class()`, causing kernel panic or Oops.

* Availability impact realistic: +1 paranoid only
  The crash is reproducible through a defined local control-plane sequence and can affect the whole system.

* Requires CAP_NET_ADMIN in typical deployments: conservative penalty considered
  Without unprivileged user namespaces or delegated netns administration, qdisc modification normally requires `CAP_NET_ADMIN`. This lowers the conservative score, but not the paranoid score because namespace-scoped CAP_NET_ADMIN can be obtainable by an unprivileged local user on many systems.

* No memory corruption or LPE primitive: +0
  The patch shows a NULL pointer dereference, not UAF, double free, arbitrary write, page-cache corruption, or privilege escalation.

* No remote reachability: +0
  The issue is triggered via rtnetlink qdisc control-plane operations, not packet receive processing.

## 3. Reachability analysis

The bug is local. In a traditional configuration, the attacker needs `CAP_NET_ADMIN` to create and modify TAPRIO qdiscs. On systems with unprivileged user namespaces enabled, an unprivileged user may create a new network namespace and obtain namespace-scoped `CAP_NET_ADMIN`, making the crash practically reachable. The affected path requires `CONFIG_NET_SCH_TAPRIO` and the TAPRIO qdisc to be available. Exploitation is realistic for DoS because the sequence is deterministic and does not require a race.

## 4. Severity interpretation

This behaves like an actionable local DoS, not an Important memory corruption issue. The demonstrated impact is a kernel NULL pointer dereference and panic. There is no evidence of confidentiality or integrity impact, no stale object reuse, no controlled overwrite, and no privilege escalation path. It should not be escalated as memory corruption, but namespace reachability makes it more important than a purely privileged admin-only crash.

## 5. One-sentence report phrase

A local TAPRIO qdisc control-plane sequence can leave a NULL child qdisc slot and later trigger a NULL pointer dereference during RTM_GETTCLASS class dump, causing a kernel panic on systems where TAPRIO and namespace-scoped CAP_NET_ADMIN are available.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED.

Manual review is recommended because the bug can be reachable by unprivileged local users through user namespaces on some systems, but current evidence supports DoS only and does not show memory corruption or privilege escalation.

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

Patch: net/sched: taprio: fix NULL pointer dereference in class dump [ Upstream
Commit: ec2501e361b08b50bcb1e7b3253fc861abbda28d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ec2501e361b08b50bcb1e7b3253fc861abbda28d

Changed files:
  net/sched/sch_taprio.c
  net/sched/sch_api.c
  net/core/rtnetlink.c
  net/netlink/af_netlink.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=ec2501e361b08b50bcb1e7b3253fc861abbda28d

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

The original Linux kernel CVE announcement for CVE-2026-45845 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45845

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: Not available
  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: 3
  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).