[CVE-2026-74382][LOW] net/sched: cls_bpf: prevent unbounded recursion in offload rollback [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-74382
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: net/sched: cls_bpf: prevent unbounded recursion in offload rollback [ Upstream
Commit: a018f208ab7512380bd4cf670064d48cba00a1b1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a018f208ab7512380bd4cf670064d48cba00a1b1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74382
Analysis date: Sat, 15 Aug 2026 12:29:08 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A privileged local user who can manage cls_bpf hardware offload filters may trigger unbounded rollback recursion after repeated offload replace failures, causing kernel stack exhaustion and denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-74382 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74382

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.

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

CVE-2026-74382	LOW	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:N/I:N/A:H';CWE-674;**CWE-400;CWE-703;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'cls_bpf offload rollback can recurse without a bound when tc_setup_cb_replace fails during replace and the rollback attempt fails again. This consumes kernel stack through repeated cls_bpf_offload_cmd calls and can end in stack exhaustion or kernel crash. For the CVSS the PR:L is used for the paranoid score because reduced capability root, container root, or delegated CAP_NET_ADMIN may be able to manage tc filters and trigger hardware offload operations without full host administrator intent. The issue is not directly network reachable and is triggered through local tc control plane operations, not by packet traffic. Impact is denial of service only based on the patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	REMOTE OOB BPF NETWORK HARDWARE DEBUGFS LINUS 	NO	NO	checked

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

ActionableScore=1
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Conservative signals:

* Reliable kernel crash / strong DoS: +1. The commit describes unbounded recursion in `cls_bpf_offload_cmd()` until kernel stack exhaustion.
* Requires admin/root/CAP_NET_ADMIN in typical deployments: -2. Triggering requires `tc filter replace`, cls_bpf offload setup, and usually CAP_NET_ADMIN plus privileged BPF/offload configuration.
* Rare AND difficult-to-reach subsystem/configuration: -1. The issue requires cls_bpf hardware offload rollback and repeated `tc_setup_cb_replace()` failure. This is not a normal packet-processing path.

Conservative total is below zero, normalized to 0.

Paranoid signals:

* Reliable kernel crash / strong DoS: +1.
* No memory corruption primitive is supported beyond stack exhaustion. No UAF, OOB write, type confusion, refcount abuse, callback control, or attacker-controlled reclaim is shown.
* No remote/network trigger. This is a local control-plane operation, not packet traffic.
* No LPE signal. The patch context supports DoS only.

Paranoid total: 1.

## 3. Reachability analysis

The bug is reachable by a user able to configure cls_bpf traffic-control filters with hardware offload and trigger a failing replace operation. In typical deployments this requires CAP_NET_ADMIN or root-level control over networking and BPF/offload configuration. Namespace delegation could lower the practical privilege boundary in some environments, but real hardware offload access is usually not available to ordinary unprivileged containers. The path is not default-exposed to remote attackers and is not triggered by network packets. Realistic exploitation requires a driver or test device where `tc_setup_cb_replace()` fails during both the original operation and rollback.

Call-site confidence: high. The relevant caller updates are visible in the patch.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like privileged local DoS. The demonstrated failure mode is kernel stack exhaustion from unbounded recursion. There is no evidence of attacker-controlled memory corruption, privilege escalation, information disclosure, or cross-boundary policy bypass. Theoretical concern from stack overflow does not justify Important-class handling here because the patch only supports a crash-style primitive in a privileged control-plane path.

## 5. One-sentence report phrase

A privileged local user who can manage cls_bpf hardware offload filters may trigger unbounded rollback recursion after repeated offload replace failures, causing kernel stack exhaustion and denial of service.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED.

This can be auto-closed or handled as low-priority Moderate in most environments because it is privileged, local-only, offload-specific, and DoS-only with no supported LPE or memory-corruption primitive.

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

Patch: net/sched: cls_bpf: prevent unbounded recursion in offload rollback [ Upstream
Commit: a018f208ab7512380bd4cf670064d48cba00a1b1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a018f208ab7512380bd4cf670064d48cba00a1b1

Changed files:
  net/sched/cls_bpf.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=a018f208ab7512380bd4cf670064d48cba00a1b1

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

The original Linux kernel CVE announcement for CVE-2026-74382 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74382

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:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 0
  Paranoid ActionableScore: 1

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).