[CVE-2026-72390][MODERATE 7.0] net/sched: sch_teql: Introduce slaves_lock to avoid race condition and UAF [ Upstream

[CVE-2026-72390][MODERATE 7.0] net/sched: sch_teql: Introduce slaves_lock to avoid race condition and UAF [ Upstream

[AL-KERNEL]

CVE: CVE-2026-72390
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net/sched: sch_teql: Introduce slaves_lock to avoid race condition and UAF [ Upstream
Commit: 03c67781254c574ae7fa75e881239a78473bdf42
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=03c67781254c574ae7fa75e881239a78473bdf42
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72390
Analysis date: Sat, 15 Aug 2026 20:08:54 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum**:: Confirmed kernel UAF requires manual review. Conservative handling is borderline because TEQL setup usually needs CAP_NET_ADMIN and the race is timing dependent, but paranoid triage should not auto-close a demonstrated slab-use-after-free in a networking qdisc transmit path.
Manual review required: YES

Summary:
A race in sch_teql allowed concurrent TEQL slave list mutation and transmit traversal to leave a stale Qdisc pointer in teql_master_xmit, causing a confirmed slab use after free and at least local kernel crash DoS, with manual review required for possible memory corruption impact.

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

The original Linux kernel CVE announcement for CVE-2026-72390 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72390

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-2026-72390	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	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-362;*CWE-416;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race condition in sch_teql can corrupt the lifetime assumptions for the TEQL master slave qdisc list because master slaves and NEXT_SLAVE links were updated without a common writer lock and without consistent RCU protection. teql_master_xmit can traverse the list on one CPU while qdisc init or destroy paths modify or remove entries on another CPU, leaving a stale Qdisc pointer that is later dereferenced as a slab use after free. For the CVSS the PR:L is used for the paranoid score because reliable triggering normally requires local control of qdisc or network namespace configuration such as CAP_NET_ADMIN, but this may be available to a reduced capability root, container root, or delegated network administration context rather than full host administrator privileges. The issue is not directly network reachable because the dangerous mutation is a local control plane operation, although packet transmission through an already configured TEQL device can participate in the race. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to use after free memory corruption, so manual review is required.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 4)	YES	REMOTE READ LOCK DANGER INIT RACE UAF NETWORK SKB HARDWARE QDISC  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: Confirmed kernel UAF requires manual review. Conservative handling is borderline because TEQL setup usually needs CAP_NET_ADMIN and the race is timing dependent, but paranoid triage should not auto-close a demonstrated slab-use-after-free in a networking qdisc transmit path.

## 2. Signal breakdown

Triggered signals:

* Memory corruption, weak race-UAF primitive: +1
  The patch and report show a confirmed `slab-use-after-free` in `teql_master_xmit()`, but no attacker-controlled reclaim, overwrite, type confusion, callback dispatch, or refcount takeover is shown.

* Real lifetime corruption: +1
  A `Qdisc` can be freed after an RCU grace period while another CPU still holds a stale pointer into the TEQL slave list.

* Reliable kernel crash / strong DoS: +1
  KASAN reports a concrete UAF read in the transmit path, and the bug can plausibly crash the kernel.

* Local unprivileged or delegated namespace trigger, paranoid only: +1
  Typical host configuration requires `CAP_NET_ADMIN`, but user namespaces or container/delegated network administration may make qdisc configuration reachable from a reduced-privilege context.

* Networking qdisc data-plane exposure, paranoid only: +1
  The vulnerable stale pointer is dereferenced from the transmit path once TEQL is configured, so packet transmission participates in triggering the race.

Subtracting / limiting factors:

* Hard or timing-dependent race: -1 for conservative score
  The issue requires concurrent qdisc list mutation and transmit traversal.

* Requires `CAP_NET_ADMIN` in typical deployments: conservative limiting factor
  Creating or destroying TEQL qdiscs is normally a local control-plane operation requiring network administration privileges.

* Race-UAF downgrade cap applied
  Because the evidence shows stale pointer dereference and crash, but not controlled reuse or write-after-free, the conservative score is capped below Important and the paranoid score is capped at 5.

## 3. Reachability analysis

The bug is locally triggerable through TEQL qdisc configuration and concurrent packet transmission. In normal host deployments, the attacker needs `CAP_NET_ADMIN` or equivalent authority to create, modify, or destroy qdiscs. In containerized or namespace-enabled environments, this may be weaker than full host root if an attacker controls a network namespace or has delegated network administration rights.

The issue is not directly remotely reachable. Remote traffic alone is not enough unless TEQL is already configured and a local actor can race qdisc teardown or reconfiguration. TEQL is a niche qdisc and is not a default common deployment path, but it is reachable through standard Linux traffic-control mechanisms when available.

Call-site confidence: high. The patch includes the relevant mutation paths and the transmit traversal path.

## 4. Severity interpretation

This is not an ordinary low-risk cleanup bug because the report demonstrates a real `slab-use-after-free` in kernel networking code. Realistic impact is most clearly local DoS through kernel crash. Privilege escalation is not demonstrated, and the patch does not show a controlled reclaim, write primitive, callback hijack, or type confusion.

For conservative triage, this behaves like a borderline Moderate that should still be reviewed because it is confirmed memory lifetime corruption. For paranoid triage, it is an Actionable Moderate at minimum because networking UAF bugs are historically under-scored when only the crash symptom is initially shown.

## 5. One-sentence report phrase

A race in sch_teql allowed concurrent TEQL slave list mutation and transmit traversal to leave a stale Qdisc pointer in teql_master_xmit, causing a confirmed slab use after free and at least local kernel crash DoS, with manual review required for possible memory corruption impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.

YES REQUIRES MANUAL CHECK. Confirmed kernel UAF in a networking transmit path should not be auto-closed, even though the demonstrated impact is currently DoS and typical triggering requires `CAP_NET_ADMIN` or delegated namespace control.

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

Patch: net/sched: sch_teql: Introduce slaves_lock to avoid race condition and UAF [ Upstream
Commit: 03c67781254c574ae7fa75e881239a78473bdf42
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=03c67781254c574ae7fa75e881239a78473bdf42

Changed files:
  net/sched/sch_teql.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=03c67781254c574ae7fa75e881239a78473bdf42

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

The original Linux kernel CVE announcement for CVE-2026-72390 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72390

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: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: 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).