[CVE-2026-63982][LOW] net/sched: Fix ethx:ingress -> ethy:egress -> ethx:ingress mirred loop [ Upstream

[CVE-2026-63982][LOW] net/sched: Fix ethx:ingress -> ethy:egress -> ethx:ingress mirred loop [ Upstream

[AL-KERNEL]

CVE: CVE-2026-63982
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: net/sched: Fix ethx:ingress -> ethy:egress -> ethx:ingress mirred loop [ Upstream
Commit: 66f4607fe788fc7d81bce0e2f7b3726ed2f71284
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=66f4607fe788fc7d81bce0e2f7b3726ed2f71284
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63982
Analysis date: Sun, 19 Jul 2026 20:48:32 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A tc mirred ingress redirection loop can bypass existing loop detection after backlog deferral, allowing a CAP_NET_ADMIN level actor to create a persistent packet-processing loop that causes local network or CPU denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-63982 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63982

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: LOW
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-63982	LOW	CHECK WITH IMPACT FROM ORIG NN MODERATE	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-835;**CWE-400;CWE-674;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A mirred redirect loop can bypass the existing loop detection when traffic is redirected to ingress and the packet is deferred through the backlog path. The per CPU sched_mirred_dev tracking can be cleared before the packet re enters the next mirred action, so a configuration that redirects from one device ingress or egress path back into another ingress path may continue looping instead of being dropped. For the CVSS the PR:L in the paranoid score reflects environments where a reduced capability root, container root, or delegated CAP_NET_ADMIN service can configure tc rules without full host root privileges. The issue is not directly network reachable as a standalone remote bug because reliable triggering requires control over tc mirred configuration. Impact is denial of service through packet processing loops, high CPU usage, and degraded network responsiveness. No memory corruption primitive is indicated by the patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)  SKIP CVE-2026-63982 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: fe946a751d9b52b7c45ca34899723b314b79b249 YES  NO NO unknown 	MAYBE	REMOTE OOB NETWORK SKB HARDWARE TEST QDISC PACKET  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Conservative signals:

* Reliable kernel crash / strong DoS: +1. A crafted tc mirred configuration can create a packet-processing loop and cause CPU/network DoS.
* Requires admin/root/CAP_NET_ADMIN in typical deployments: -2. Creating qdisc/filter/action state with `tc` normally requires CAP_NET_ADMIN.
* Availability impact realistic: +1. The loop can persist while the tc configuration remains active and can degrade networking or CPU availability.
* Common networking packet-processing path: +1. The affected code is in `net/sched` packet redirection, but only after explicit tc configuration.

Paranoid adjustment:

* Reduced privilege CAP_NET_ADMIN interpretation: +1 relative to conservative. In container or delegated network administration setups, the actor may be container root or a service account with CAP_NET_ADMIN rather than full host root.

Not applied:

* No remote reachable bonus. Remote packets may stimulate the loop only after a privileged local tc configuration exists.
* No memory corruption bonus. The patch shows loop-depth accounting and recursion-limit enforcement, not UAF, OOB write, double-free, or type confusion.
* No LPE bonus. There is no plausible privilege-escalation primitive in the patch context.

## 3. Reachability analysis

The bug is triggered by configuring tc `mirred` redirects that bounce packets between ingress and egress paths. In normal deployments this requires CAP_NET_ADMIN, so the conservative interpretation is privileged local control-plane access. Namespace or container setups can lower the practical privilege level if CAP_NET_ADMIN is delegated to a container or service, but this still requires control over tc configuration. The path is not directly network reachable as a standalone remote vulnerability.

## 4. Severity interpretation

This behaves like an ordinary Moderate / Low-like DoS issue, not an Important-class vulnerability. The realistic impact is CPU and network availability degradation from a mirred packet loop. Theoretical impact remains limited because the patch does not indicate memory corruption, security-boundary bypass, information disclosure, or privilege escalation.

## 5. One-sentence report phrase

A tc mirred ingress redirection loop can bypass existing loop detection after backlog deferral, allowing a CAP_NET_ADMIN level actor to create a persistent packet-processing loop that causes local network or CPU denial of service.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED.

This is a configuration-dependent DoS-only bug with no memory corruption or privilege-escalation primitive shown by the patch.

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

Patch: net/sched: Fix ethx:ingress -> ethy:egress -> ethx:ingress mirred loop [ Upstream
Commit: 66f4607fe788fc7d81bce0e2f7b3726ed2f71284
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=66f4607fe788fc7d81bce0e2f7b3726ed2f71284

Changed files:
  net/sched/act_mirred.c
  net/tc_act/tc_mirred.h
  net/tc_wrapper.h

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=66f4607fe788fc7d81bce0e2f7b3726ed2f71284

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

The original Linux kernel CVE announcement for CVE-2026-63982 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63982

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: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: 1
  Paranoid ActionableScore: 2

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).