[CVE-2026-72125][MODERATE 7.0] can: isotp: fix use-after-free race with concurrent NETDEV_UNREGISTER

[CVE-2026-72125][MODERATE 7.0] can: isotp: fix use-after-free race with concurrent NETDEV_UNREGISTER

[AL-KERNEL]

CVE: CVE-2026-72125
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: can: isotp: fix use-after-free race with concurrent NETDEV_UNREGISTER
Commit: 0b811c4bbe3ec9ad611e90a540fe8b51b3bb8a96
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0b811c4bbe3ec9ad611e90a540fe8b51b3bb8a96
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72125
Analysis date: Sat, 15 Aug 2026 06:38:13 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race between CAN ISO-TP socket release and NETDEV_UNREGISTER can leave a stale CAN receive filter pointing to a freed socket, allowing a later CAN callback to trigger a kernel UAF with at least DoS impact and possible memory corruption consequences.

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

The original Linux kernel CVE announcement for CVE-2026-72125 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72125

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
======================================================================

CVE-2026-72125	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:H/I:H/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A use after free race in CAN ISO TP can leave a stale CAN receive filter pointing to a freed socket when isotp_release runs concurrently with NETDEV_UNREGISTER. During device unregister the net device can already be removed from the ifindex hash, so release may fail to find it, skip can_rx_unregister, and free the socket while the filter remains active. A later CAN receive or echo callback can dereference the stale socket pointer, causing a kernel crash and potentially allowing memory corruption effects. For the CVSS the PR:L is used for the paranoid score because reliable triggering requires local code execution with access to CAN ISO TP sockets and a way to influence netdev unregister, which may be available to a local user through delegated CAP_NET_ADMIN, a container root context, or user namespace based test setups. The issue is not directly reachable from a remote IP network and is tied to local CAN network device lifecycle operations. Impact is at least local denial of service via kernel crash and in the worst case may allow confidentiality or integrity impact due to use after free memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	INIT RACE UAF TIMER HARDWARE LINUS KPANIC  DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	YES	NO	checked

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

ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Generic memory corruption: +2. This is a real UAF pattern: a stale CAN RX filter can keep a pointer to a freed ISO-TP socket.
* Real lifetime corruption: +1. The bug is caused by incorrect lifetime synchronization between `isotp_release()`, `NETDEV_UNREGISTER`, notifier removal, and socket free.
* Reliable kernel crash / strong DoS: +1. A later CAN receive or echo callback may dereference the freed socket pointer.
* Local low-privileged or delegated trigger concern: +1. Reliable triggering likely needs local CAN ISO-TP socket access and influence over CAN netdev unregister, but this may be reachable through delegated `CAP_NET_ADMIN`, container root, or namespace-based setups.
* Hard race / timing required: -1. The vulnerable window depends on concurrent `isotp_release()` and `NETDEV_UNREGISTER`.

Paranoid additional signals:

* Strong LPE plausibility: +2 instead of weak concern. The stale filter creates a callback path to freed socket memory, which is more serious than a pure stale pointer dereference.
* Practical exploit chain strongly implied: +1. The chain is directly described: unregister unlists device by ifindex, release misses cleanup, socket is freed, stale CAN filter remains, later callback uses freed socket.
* No remote/network score. This is CAN socket and netdev lifecycle driven, not directly reachable over an IP network.

Call-site confidence: high. The patch shows the relevant bind, release, notifier, filter registration, filter unregistration, and callback-related paths.

## 3. Reachability analysis

The bug is locally reachable when CAN ISO-TP is enabled and a socket is bound to a CAN net device. Reliable triggering requires racing socket release with `NETDEV_UNREGISTER`. In typical host deployments, unregistering or creating CAN devices often requires `CAP_NET_ADMIN`, but this should not always be treated as full host-root because delegated network administration, container root, or namespace setups may reduce the effective privilege barrier. The path is not remotely reachable via normal IP networking. Realistic exploitation requires CAN ISO-TP availability and control over the device lifecycle or a setup where device unregister can be induced.

## 4. Severity interpretation

This is not an ordinary Moderate cleanup issue. It is a race-based UAF with a stale callback-capable CAN filter pointing at freed socket memory. The realistic impact is at least local kernel crash / DoS. The stronger concern is that the stale callback into freed socket memory may become a memory-corruption primitive under favorable reclaim conditions, although the patch does not demonstrate a reliable LPE exploit. Therefore the conservative score is Actionable Moderate, while the paranoid score is a Strong Important candidate for manual review.

## 5. One-sentence report phrase

A race between CAN ISO-TP socket release and NETDEV_UNREGISTER can leave a stale CAN receive filter pointing to a freed socket, allowing a later CAN callback to trigger a kernel UAF with at least DoS impact and possible memory corruption consequences.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a race-based UAF with a stale callback path to freed socket memory, not a simple NULL dereference or resource leak.

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

Patch: can: isotp: fix use-after-free race with concurrent NETDEV_UNREGISTER
Commit: 0b811c4bbe3ec9ad611e90a540fe8b51b3bb8a96
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0b811c4bbe3ec9ad611e90a540fe8b51b3bb8a96

Commit description:

isotp_release() looked up the bound network device via dev_get_by_index()
using the stored ifindex. During device unregistration the device is
unlisted from the ifindex hash before the NETDEV_UNREGISTER notifier
chain runs, so a concurrent isotp_release() could find no device, skip
can_rx_unregister() entirely, and still proceed to free the socket.
Since isotp_release() had already removed itself from the isotp
notifier list at that point, isotp_notify() would never get a chance to
clean up either, leaving a stale CAN filter that keeps pointing at the
freed socket.

Fix this the same way raw.c already does: hold a tracked reference to
the bound net_device in the socket (so->dev/so->dev_tracker) from
bind() onward instead of re-resolving it from the ifindex, and
serialize bind()/release() with rtnl_lock() so that so->dev is always
consistent with what the NETDEV_UNREGISTER notifier sees. so->dev
stays valid regardless of ifindex-hash unlisting, and is only ever
cleared by whichever of isotp_release()/isotp_notify() gets there
first, so the filter is always removed exactly once.

isotp_bind() now rejects a (re)bind with -EAGAIN while so->[tx|rx].state
isn't ISOTP_IDLE yet, so a timer left running by a prior
NETDEV_UNREGISTER can't act on a newly bound so->ifindex. Both checks
share the same lock_sock() section, so there is no window in which a
concurrent isotp_notify() clearing so->bound could be missed.

Fixes: e057dd3 ("can: add ISO 15765-2:2016 transport protocol")
Reported-by: sashiko-bot@kernel.org
Closes: https://lore.kernel.org/linux-can/20260707101420.47F261F000E9@smtp.kernel.org/
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://patch.msgid.link/20260712-isotp-fixes-v10-2-793a1b1ce17f@hartkopp.net
Cc: stable@kernel.org
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Changed files:
  net/can/isotp.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=0b811c4bbe3ec9ad611e90a540fe8b51b3bb8a96

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

The original Linux kernel CVE announcement for CVE-2026-72125 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72125

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:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 5
  Paranoid ActionableScore: 7

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).