[CVE-2026-53014][MODERATE 7.0] net/sched: act_mirred: fix wrong device for mac_header_xmit check in tcf_blockcast_redir [ Upstream

[CVE-2026-53014][MODERATE 7.0] net/sched: act_mirred: fix wrong device for mac_header_xmit check in tcf_blockcast_redir [ Upstream

[AL-KERNEL]

CVE: CVE-2026-53014
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net/sched: act_mirred: fix wrong device for mac_header_xmit check in tcf_blockcast_redir [ Upstream
Commit: 8fda5174286119addd28473fb2ec5bdf521c05a8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8fda5174286119addd28473fb2ec5bdf521c05a8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53014
Analysis date: Wed, 24 Jun 2026 13:54:25 -0400
ActionableScore: 5
ActionableScore lower bound: 2
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A wrong device lookup in `tcf_blockcast_redir()` can apply an incorrect MAC header handling mode during mirred blockcast redirection, corrupting skb header state and potentially causing a kernel panic when mixed device types are used.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-53014 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53014

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-2026-53014	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';CWE-682;CWE-119;*CWE-787;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'tcf_blockcast_redir() can pass the wrong mac_header_xmit value to tcf_mirred_to_dev() because the code checked the next device in the block instead of the device currently used for redirection. With mixed device types in the same block, for example ethernet veth and tunnel devices, this can make skb header handling choose the wrong push or pull operation and corrupt skb header state. The practical impact is at least denial of service because skb_push_rcsum with an incorrect mac_len can exhaust skb headroom and trigger a kernel panic. For the CVSS the PR:N value is used in the paranoid score only for deployments where the vulnerable tc blockcast configuration already exists and attacker controlled packets can reach the matching rule. Otherwise local CAP_NET_ADMIN or equivalent control of tc configuration is required. The issue is potentially reachable from network traffic only after such non default traffic control configuration is present.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	REMOTE DANGER NETWORK SKB HARDWARE PACKET  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Constrained kernel buffer corruption: +1. The wrong `mac_header_xmit` value can cause incorrect skb MAC header push or pull handling, but the patch does not show attacker-controlled arbitrary overwrite.
* Reliable kernel crash / strong DoS: +1. The commit explicitly says incorrect `mac_len` can exhaust skb headroom and panic.
* Common packet-processing path: +1. This is in `net/sched` packet redirection handling, but only for a specific tc action setup.
* Requires CAP_NET_ADMIN in typical deployments: -2. Creating the vulnerable `tc` blockcast mirred setup normally requires traffic-control administration privileges.

Paranoid signals:

* Network-triggerable after vulnerable configuration exists: +2. If the tc blockcast configuration is already present, attacker-controlled packets reaching the matching rule may trigger the bug.
* Constrained kernel buffer corruption: +1. The corruption affects skb header state and headroom handling.
* Reliable kernel crash / strong DoS: +1. Kernel panic is explicitly described.
* Common packet-processing path: +1. The vulnerable path processes packets, not only offline configuration.
* Special non-default configuration required: -1. Triggering requires mixed device types in a mirred blockcast setup.

No extra LPE, confidentiality, or integrity bonus is added because the patch supports skb header corruption and panic, but not a concrete reclaim, arbitrary write, type confusion, or data disclosure primitive.

## 3. Reachability analysis

Typical setup requires a local privileged actor with `CAP_NET_ADMIN` to create the vulnerable `tc` mirred blockcast configuration. In that conservative model, this is a privileged local DoS bug.

In the paranoid model, the vulnerable configuration may already exist on a router, container host, testbed, or service-managed networking node. In that case, a remote or adjacent attacker may only need to send packets that match the configured rule, so the trigger can become network-driven. Namespaces can matter because `CAP_NET_ADMIN` may be delegated inside containers or network namespaces, but host impact depends on how the affected devices and qdiscs are exposed.

The path is not default-enabled in the sense that ordinary systems do not normally run mixed-device blockcast mirred tc actions, but it is part of the Linux networking packet-processing stack.

## 4. Severity interpretation

This behaves more like an Actionable Moderate than an ordinary Moderate because the patch context explicitly describes skb header corruption and a kernel panic path. It is not a Strong Important candidate by default because reliable exploitation usually depends on a non-default tc configuration and the corruption primitive appears constrained to skb header handling.

Theoretical memory corruption potential exists through corrupted skb header state and headroom exhaustion. Realistic evidence currently supports DoS via panic, not privilege escalation or arbitrary code execution.

## 5. One-sentence report phrase

A wrong device lookup in `tcf_blockcast_redir()` can apply an incorrect MAC header handling mode during mirred blockcast redirection, corrupting skb header state and potentially causing a kernel panic when mixed device types are used.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Manual review is required because the bug is in a packet-processing path, can become packet-triggerable after configuration, and the commit explicitly mentions skb header corruption plus panic rather than a simple validation failure.

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

Patch: net/sched: act_mirred: fix wrong device for mac_header_xmit check in tcf_blockcast_redir [ Upstream
Commit: 8fda5174286119addd28473fb2ec5bdf521c05a8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8fda5174286119addd28473fb2ec5bdf521c05a8

Changed files:
  net/sched/act_mirred.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=8fda5174286119addd28473fb2ec5bdf521c05a8

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

The original Linux kernel CVE announcement for CVE-2026-53014 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53014

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:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 6.4

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: 2
  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).