[CVE-2026-72338][MODERATE 7.0] net/sched: act_pedit: fix TOCTOU heap OOB write in tc offload [ Upstream

[CVE-2026-72338][MODERATE 7.0] net/sched: act_pedit: fix TOCTOU heap OOB write in tc offload [ Upstream

[AL-KERNEL]

CVE: CVE-2026-72338
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: net/sched: act_pedit: fix TOCTOU heap OOB write in tc offload [ Upstream
Commit: 0d8532a5e972a5351cf4ee4a435e0d65cbba8f23
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0d8532a5e972a5351cf4ee4a435e0d65cbba8f23
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72338
Analysis date: Sun, 16 Aug 2026 02:11:49 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A TOCTOU race in net/sched act_pedit tc offload can cause an attacker-controlled heap out-of-bounds write during flow_action setup, requiring CAP_NET_ADMIN or equivalent delegated tc control and potentially leading to kernel crash or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-72338 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72338

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-2026-72338	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	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-367;*CWE-787;CWE-122;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H';BEST CVSS score: '7';DESCR 'A TOCTOU race in net/sched act_pedit offload can make the flow_action buffer size calculation use an older pedit key count while the later fill path observes a larger key count. This can cause a heap out-of-bounds write in tcf_pedit_offload_act_setup with attacker-controlled content into an adjacent slab object. For the CVSS the PR:L is used for the paranoid score because triggering requires local control of tc actions through CAP_NET_ADMIN or an equivalent delegated network administration context, which can exist in containers or service accounts and is not full host root in practical risk terms. The issue is not directly network reachable and is triggered through rtnetlink/tc control plane operations rather than packet traffic. Impact is at least local denial of service and in worst case may allow confidentiality and integrity impact or privilege escalation due to kernel heap memory corruption. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	REMOTE WRITE KASAN OOB LOCK RACE HARDWARE KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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

ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative scoring:

* Memory corruption, strong corruption primitive: +2
  KASAN confirms a slab out-of-bounds write in `tcf_pedit_offload_act_setup()`. The commit explicitly states attacker-controlled content can be written into an adjacent slab object.

* Strong LPE plausibility: +2
  A local attacker with sufficient tc control can influence pedit keys and trigger a kernel heap OOB write. This is a plausible privilege-escalation class primitive, even though no working LPE chain is shown.

* Reliable kernel crash / strong DoS: +1
  KASAN reports a concrete slab OOB write. Kernel crash is realistic.

* Confidentiality impact plausible: +1
  Heap corruption can plausibly affect adjacent objects and kernel state, though no direct info leak is demonstrated.

* Integrity impact plausible: +1
  Attacker-controlled heap OOB write makes integrity impact plausible.

* Requires CAP_NET_ADMIN in typical deployments: -2
  The trigger is through tc/rtnetlink control plane and normally requires CAP_NET_ADMIN.

Conservative total: 5

Paranoid adjustments:

* Broad/common networking control-plane exposure: +1
  `net/sched`, tc actions, cls_flower, and rtnetlink are common kernel networking components, even though this is not packet-path remote exposure.

* Reduced privilege / delegated CAP_NET_ADMIN interpretation: -1 instead of -2
  CAP_NET_ADMIN may be delegated to containers, service accounts, or network-management components and is not always equivalent to full host root in practical risk terms.

Paranoid total: 7

No race penalty applied because the commit states the independent locking domains make the TOCTOU race reachable in practice.

## 3. Reachability analysis

The bug is locally reachable through tc/rtnetlink configuration of flower and pedit offload paths. In normal host deployments, this requires CAP_NET_ADMIN, so it is not a fully unprivileged local trigger. It is not directly network reachable because packet traffic alone does not trigger the vulnerable sizing/fill race.

Namespaces and containers matter. If CAP_NET_ADMIN is delegated inside a container or to a reduced-privilege network service, the practical privilege requirement can be closer to PR:L than PR:H. The affected path is not a rare debug-only path, but it does require tc offload-related configuration and a race between action update and classifier/offload setup.

Call-site confidence: high. The patch includes both sizing and fill call sites, plus the capacity checks in `tc_setup_action()` and `tcf_pedit_offload_act_setup()`.

## 4. Severity interpretation

This is not an ordinary Moderate resource leak or validation-only bug. It is a TOCTOU race with a demonstrated heap OOB write and attacker-controlled content into an adjacent slab object.

Realistic exploitation still requires CAP_NET_ADMIN or equivalent delegated control and successful race timing. That keeps the conservative score in Actionable Moderate territory. The paranoid interpretation is Strong Important candidate because the primitive is kernel heap memory corruption and CAP_NET_ADMIN is often delegated below full host-root authority.

## 5. One-sentence report phrase

A TOCTOU race in net/sched act_pedit tc offload can cause an attacker-controlled heap out-of-bounds write during flow_action setup, requiring CAP_NET_ADMIN or equivalent delegated tc control and potentially leading to kernel crash or privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: demonstrated attacker-controlled kernel heap OOB write, practical race reachability, and possible reduced-privilege CAP_NET_ADMIN exposure make this unsuitable for auto-close.

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

Patch: net/sched: act_pedit: fix TOCTOU heap OOB write in tc offload [ Upstream
Commit: 0d8532a5e972a5351cf4ee4a435e0d65cbba8f23
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0d8532a5e972a5351cf4ee4a435e0d65cbba8f23

Changed files:
  include/net/tc_act/tc_pedit.h
  net/sched/act_api.c
  net/sched/act_pedit.c
  net/sched/cls_api.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=0d8532a5e972a5351cf4ee4a435e0d65cbba8f23

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

The original Linux kernel CVE announcement for CVE-2026-72338 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72338

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:H/UI:N/S:U/C:H/I:H/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: 5
  Paranoid ActionableScore: 7

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).