[CVE-2026-74677][MODERATE 7.0] net: usb: ipheth: fix carrier_work UAF on disconnect

[CVE-2026-74677][MODERATE 7.0] net: usb: ipheth: fix carrier_work UAF on disconnect

[AL-KERNEL]

CVE: CVE-2026-74677
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: net: usb: ipheth: fix carrier_work UAF on disconnect
Commit: d07133fe1befae9a1e4c4c5e46ef0b73d2992020
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d07133fe1befae9a1e4c4c5e46ef0b73d2992020
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74677
Analysis date: Sat, 22 Aug 2026 16:13:58 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in the ipheth USB network driver can re-arm carrier_work after close or disconnect, leaving delayed work pending after free_netdev and causing a confirmed slab-use-after-free that is realistically a local or device-mediated kernel crash DoS.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74677 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74677

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-2026-74677	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A use after free can occur in the ipheth USB network driver because carrier_work can be re armed by ipheth_sndbulk_callback after ipheth_close has already drained the delayed work. During disconnect, an in flight TX URB may complete with an error after unregister_netdev and ipheth_close, which can queue carrier_work again while the netdev private area that embeds the work item is later freed. A later timer or workqueue execution can dereference freed memory and crash the kernel. For the CVSS the PR:L is used for the paranoid score because a reduced local actor with delegated device or network control may be able to influence interface state and disconnect timing, even though the reported reproducer was driven as root. The issue is not network reachable in the normal IP packet sense and usually requires local USB device interaction or local control of the affected interface. Impact is at least local denial of service via kernel crash and in worst case may allow limited confidentiality or integrity impact due to the UAF class, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	USB UAF NETWORK HARDWARE LINUS KPANIC  KPANIC LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS 	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

Conservative signals:

* Memory corruption, weak primitive: +1
  Confirmed race-dependent slab-use-after-free, but no demonstrated reclaim, overwrite, attacker-controlled replacement, or LPE primitive.
* Real lifetime corruption: +1
  Delayed work can survive netdev teardown and later dereference freed netdev private data.
* Reliable kernel crash / strong DoS: +1
  KASAN reproducer reports 15 of 15 unpatched boots hitting slab-use-after-free.
* Firmware-mediated or device-mediated external influence: +1
  Trigger depends on behavior of an attached USB device and URB completion timing.
* Privileged kernel/device-management lifetime path: +1
  The bug is in USB network driver disconnect/open/close lifetime management.
* Requires admin/root/CAP-like control in demonstrated path: -2
  The reproducer is driven as root and needs link down plus unplug/device control.

Paranoid adjustment:

* Local reduced-privilege or delegated-control trigger concern: +1
  In some environments, a local actor with delegated device or network-interface control may influence interface state and disconnect timing without full host-root equivalence.
* Race-UAF cap applied.
  Conservative score is capped at 4 and paranoid score at 5 because this is a race-dependent UAF without a demonstrated controlled reclaim, write-after-free, object replacement, or privilege escalation primitive.

## 3. Reachability analysis

The bug is not remotely reachable through normal IP packet traffic. Realistic triggering requires an affected ipheth USB network device, a TX URB in flight, interface close or link-down state, and disconnect or unplug timing that lets the URB completion re-arm carrier_work after it was drained. The supplied reproducer uses dummy_hcd and raw-gadget and is explicitly described as root-driven.

Namespaces or containers may matter only if device or network-interface management is delegated. A normal unprivileged local user typically cannot control USB disconnect and ipheth interface state reliably. However, reduced-capability root, container root with delegated device access, or a service managing USB networking could make PR:L a defensible paranoid interpretation.

## 4. Severity interpretation

This is more than an ordinary cleanup bug because the patch fixes a confirmed UAF in delayed work lifetime management. Realistic impact is mainly local DoS through kernel crash. Theoretical memory-corruption concern exists because the callback runs after the embedded work item and netdev private area are freed, but the available evidence does not show attacker-controlled reclaim, overwrite, type confusion, or privilege escalation.

This should be treated as an Actionable Moderate at minimum rather than auto-closed. It is not a strong Important candidate on the supplied evidence because exploitation needs local or physical/device control and no concrete privilege-escalation primitive was developed.

## 5. One-sentence report phrase

A race in the ipheth USB network driver can re-arm carrier_work after close or disconnect, leaving delayed work pending after free_netdev and causing a confirmed slab-use-after-free that is realistically a local or device-mediated kernel crash DoS.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: confirmed UAF plus async workqueue lifetime mismatch. No demonstrated LPE primitive is present, but the bug class and reliable KASAN reproduction make it inappropriate for automatic closure.

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

Patch: net: usb: ipheth: fix carrier_work UAF on disconnect
Commit: d07133fe1befae9a1e4c4c5e46ef0b73d2992020
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d07133fe1befae9a1e4c4c5e46ef0b73d2992020

Commit description:

ipheth_sndbulk_callback() re-arms the carrier-check work on any
non-zero URB status:

	else
		schedule_delayed_work(&dev->carrier_work, 0);

Nothing ties that to the interface being up, so the work can be armed
again after ipheth_close() has already drained it, and stay armed
until the netdev whose private area embeds it is freed.

On unplug with a TX URB in flight, ipheth_disconnect() drains the work
through unregister_netdev() -> ipheth_close() ->
cancel_delayed_work_sync() and only then calls ipheth_kill_urbs().
usb_kill_urb() completes the in-flight TX URB with -ENOENT, so
ipheth_sndbulk_callback() runs after the drain and re-arms
carrier_work.

The same completion also re-arms the work if the interface is only
brought down while a TX URB is in flight, and
ipheth_carrier_check_work() then keeps re-queueing itself once a
second. unregister_netdev() does not call ipheth_close() for an
already-down interface, so nothing drains it on the later unplug
either.

In both cases free_netdev() frees the netdev while carrier_work is
still pending, and ipheth_carrier_check_work() dereferences freed
memory.

Tie the work to the interface state instead of chasing the completion:
disable it in ipheth_close() and enable it in ipheth_open(), so a
schedule_delayed_work() from the URB completion is a no-op whenever
the interface is not up. disable_delayed_work_sync() also waits for a
running instance, so it fully replaces the cancel_delayed_work_sync()
it takes the place of. The work starts out disabled in ipheth_probe()
so the enable/disable counts balance from the first open.

Reproduced under KASAN on linux-next (next-20260731) with dummy_hcd and
raw-gadget standing in for the device, driving the second path above (the
interface is already down, so unregister_netdev() does not call
ipheth_close()): 15 of 15 unpatched boots report a slab-use-after-free in
__run_timers(), freed by ipheth_disconnect() and re-armed from
ipheth_sndbulk_callback() via queue_delayed_work_on(). The
same trigger on a kernel differing only by this patch reports 0 of 15,
and the carrier check still functions across open/close cycles.

The reproducer needs an attached USB device that stops draining bulk OUT,
plus a link down and unplug, driven as root. It is not a privilege
boundary crossing and no exploit primitive was developed.

Found by 0sec ( https://0sec.ai ).

Fixes: bb1b40c ("usbnet: ipheth: prevent TX queue timeouts when device not ready")
Cc: stable@vger.kernel.org
Signed-off-by: Doruk Tan Ozturk <doruk@0sec.ai>
Link: https://patch.msgid.link/20260802120602.42595-1-doruk@0sec.ai
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/net/usb/ipheth.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=d07133fe1befae9a1e4c4c5e46ef0b73d2992020

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

The original Linux kernel CVE announcement for CVE-2026-74677 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74677

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:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 4
  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: 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).