[CVE-2026-90058][LOW] net/sched: bound qdisc_pkt_len to prevent qdisc soft lockup [ Upstream

[CVE-2026-90058][LOW] net/sched: bound qdisc_pkt_len to prevent qdisc soft lockup [ Upstream

[AL-KERNEL]

CVE: CVE-2026-90058
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: net/sched: bound qdisc_pkt_len to prevent qdisc soft lockup [ Upstream
Commit: 4f0f4b09a95ef602fbdae948326beadd9c20eab3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4f0f4b09a95ef602fbdae948326beadd9c20eab3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90058
Analysis date: Thu, 17 Sep 2026 16:19:23 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-90058 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90058

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-2026-90058	LOW	https://www.kernelcve.org/list/?q=CVE-2026-90058 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-400;*CWE-835;CWE-770;BEST CVSS score: '5.5';DESCR 'A crafted TCA_STAB can amplify qdisc_pkt_len for an ordinary packet to about 1 GiB. DRR and ETS deficit schedulers can then execute billions of refill iterations while holding the qdisc lock when the configured quantum is 1. A single packet can consequently cause a CPU soft lockup or RCU stall and may panic the kernel when kernel.softlockup_panic is enabled. For the CVSS the PR:L reflects that a local unprivileged user can configure the required qdisc after obtaining namespace local CAP_NET_ADMIN in a permitted user and network namespace. The issue is not directly network reachable because packet traffic alone cannot install the crafted qdisc configuration. Impact is denial of service only. No memory corruption, information disclosure, or privilege escalation primitive is present in the affected calculation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)  SKIP CVE-2026-90058 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	REMOTE DEADLOCK DANGER LINUS QDISC PACKET  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=YES
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Positive signals:

* +1 Local unprivileged trigger. The supplied evidence establishes the complete trigger from a fresh user and network namespace using namespace-local CAP_NET_ADMIN.
* +1 Reliable strong DoS. One packet under the crafted DRR or ETS configuration can cause billions of deficit-refill iterations, a CPU soft lockup, an RCU stall, or a panic when softlockup panic is enabled.

Negative signals:

* No negative points. Host-admin privilege, unusual hardware, a difficult race, and prior privileged setup are not established.

Material non-awarded signals:

* No memory corruption, UAF, OOB access, persistent resource leak, or authorization bypass is established.
* No remote-reachability point. Network traffic alone cannot install the malicious qdisc configuration.
* No high-control data-plane point. The attacker controls an inflated accounting value, but no memory layout, lifetime, payload destination, or kernel object reuse.
* No additional Availability point because it would double-count the same soft-lockup or panic consequence.
* No Confidentiality, Integrity, LPE, arbitrary-write, or controlled-reclaim signal.
* No broad-exposure point because the vulnerable path specifically requires DRR or ETS with a crafted TCA_STAB and tiny quantum.

3. Reachability analysis

An ordinary local user can execute `unshare -Urn`, obtain CAP_NET_ADMIN in the new namespace, create the DRR or ETS qdisc, provide the crafted TCA_STAB, configure quantum 1, and send the triggering packet. The supplied description therefore establishes both below-host-admin reachability and a complete namespace-scoped trigger.

No separate host-admin provisioning is required when unprivileged user namespaces are enabled. Required kernel configuration includes CONFIG_NET_SCHED and either CONFIG_NET_SCH_DRR or CONFIG_NET_SCH_ETS. No special hardware, boot mode, or race timing is involved. The trigger is deterministic after configuration.

4. Primitive and severity interpretation

The exact primitive is algorithmic CPU exhaustion caused by an attacker-controlled packet-length accounting value. The inflated value makes a deficit scheduler perform an excessive number of iterations while holding the qdisc lock.

This is CLASS_C because the demonstrated behavior is a soft lockup, RCU stall, or panic without an independently useful corruption or lifetime primitive. It is neither an active structured-object UAF nor fixed stale storage. There is no release, repeated refcount mutation, semantic reinterpretation, or security-boundary bypass.

The demonstrated consequence is local host denial of service. Stronger consequences such as information disclosure, kernel memory modification, or privilege escalation are unsupported. ImportantCandidate is NO because no Important-preserving primitive remains unresolved. AutoDowngradeAllowed is YES because this is a bounded DoS-only defect with a well-defined trigger and fix.

Likely operational severity is ordinary Moderate.

5. One-sentence report phrase

A local unprivileged user with attacker-obtainable namespace CAP_NET_ADMIN can configure a crafted TCA_STAB that makes DRR or ETS spin under the qdisc lock, causing a soft lockup, RCU stall, or kernel panic without memory corruption or privilege escalation.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The supplied evidence fully establishes a deterministic namespace-local DoS and does not leave a corruption, lifetime, authorization, or cross-boundary primitive unresolved.

7. Call-site confidence

Call-site confidence: high

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

Patch: net/sched: bound qdisc_pkt_len to prevent qdisc soft lockup [ Upstream
Commit: 4f0f4b09a95ef602fbdae948326beadd9c20eab3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4f0f4b09a95ef602fbdae948326beadd9c20eab3

Changed files:
  include/net/pkt_sched.h
  net/sched/sch_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=4f0f4b09a95ef602fbdae948326beadd9c20eab3

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

The original Linux kernel CVE announcement for CVE-2026-90058 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90058

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: unknown
  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).