[CVE-2026-72124][MODERATE REGULAR] can: isotp: serialize TX state transitions under so->rx_lock

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

CVE: CVE-2026-72124
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: can: isotp: serialize TX state transitions under so->rx_lock
Commit: 0b05eca9589f609e2491b528dccf683168a4cda8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0b05eca9589f609e2491b528dccf683168a4cda8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72124
Analysis date: Sat, 15 Aug 2026 03:45:59 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline Moderate, manual review recommended
Manual review required: YES

Summary:
A race in CAN ISO-TP TX state handling can let sendmsg, RX Flow Control or echo processing, and hrtimer callbacks act on stale transfer state, causing unrelated transfer corruption or ISO-TP communication DoS on systems where local users or adjacent CAN nodes can influence the socket traffic.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-72124 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72124

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 REGULAR
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-2026-72124	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H';CWE-362;CWE-667;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '5.9';DESCR 'A race in CAN ISO TP TX state handling can let sendmsg, RX Flow Control or local echo processing, and hrtimer callbacks observe stale or mid claim transfer state. This may corrupt an unrelated transfer, report an error against the wrong transfer, or leave ISO TP communication stalled. For the CVSS the PR:N in the paranoid vector assumes an adjacent CAN bus attacker can inject timing sensitive Flow Control or echo relevant frames while a victim ISO TP socket is already transmitting, so no local account on the host is required. The issue is adjacent network reachable on systems where untrusted nodes can send CAN frames to the interface, but it is not an Internet routable TCP/IP bug. Impact is mainly denial of service or limited integrity impact to ISO TP transfers. There is no clear evidence of kernel memory corruption or privilege escalation from this patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline Moderate, manual review recommended (with actual score 3)	YES	LOCK DEADLOCK INIT RACE ERRORPATH SKB DMAorINTERRUPT IMPROVEONLY TIMER LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Borderline Moderate, manual review recommended**::

## 2. Signal breakdown

Conservative:

* Local unprivileged trigger: +1. A local process with access to CAN ISO-TP sockets can exercise `sendmsg()` and interact with TX state transitions.
* Integrity impact plausible: +1. The commit explicitly says a stale frame or timer callback could corrupt an unrelated transfer, but this is protocol state integrity, not kernel memory integrity.
* Availability impact realistic: +1. The race can stall or break ISO-TP communication and report errors against the wrong transfer.
* Hard or unreliable race / special timing required: -1. The issue depends on timing between `sendmsg()`, RX Flow Control or echo handling, and hrtimer callbacks.

Paranoid delta:

* Adjacent network-triggerable interpretation: +1 net increase. A node on the same CAN bus may influence Flow Control timing while a victim socket is transmitting. This is adjacent-network exposure, not Internet-reachable remote exposure.

Not awarded:

* No generic memory corruption bonus. The patch shows state-machine corruption, not UAF, OOB write, double-free, type confusion, or attacker-controlled reclaim.
* No LPE bonus. There is no concrete privilege escalation primitive.
* No reliable kernel crash bonus. The patch does not show a kernel panic or host-wide crash path.
* No broad networking-core exposure bonus. CAN ISO-TP is specialized and not a common TCP/IP packet path.

Call-site confidence: high. The relevant send, RX, echo, timer, and release paths are visible in the provided diff.

## 3. Reachability analysis

A local user or process that can create and use CAN ISO-TP sockets can trigger the local path. Privilege requirements depend on product policy for CAN socket access and interface exposure. In many deployments CAN access is limited to privileged services or specialized applications, but it is not equivalent to full host root if delegated to a service or container.

The paranoid case assumes an adjacent CAN bus attacker can inject timing-sensitive Flow Control or echo-relevant traffic while a legitimate host process is transmitting. This makes the issue network-adjacent, but not generally reachable over routable IP networks or the public Internet.

The subsystem is not broadly enabled on all servers, but it is relevant in automotive, industrial, embedded, and test systems using SocketCAN ISO-TP.

## 4. Severity interpretation

This behaves like a Borderline Moderate issue with manual review recommended. The realistic impact is corruption of ISO-TP transfer state, wrong-transfer error reporting, or communication DoS. Theoretical impact does not currently rise to kernel memory corruption or privilege escalation because the patch does not show stale freed object use, writable stale object access, callback control, refcount misuse, or an arbitrary write primitive.

The paranoid score is higher only because an adjacent CAN attacker may influence the RX/timer side of the race without a local account on the host.

## 5. One-sentence report phrase

A race in CAN ISO-TP TX state handling can let sendmsg, RX Flow Control or echo processing, and hrtimer callbacks act on stale transfer state, causing unrelated transfer corruption or ISO-TP communication DoS on systems where local users or adjacent CAN nodes can influence the socket traffic.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is a timing-dependent network protocol state-machine race with plausible adjacent-CAN influence, but no demonstrated kernel memory corruption, LPE primitive, or reliable host-wide crash.

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

Patch: can: isotp: serialize TX state transitions under so->rx_lock
Commit: 0b05eca9589f609e2491b528dccf683168a4cda8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0b05eca9589f609e2491b528dccf683168a4cda8

Commit description:

The TX state machine (so->tx.state) is driven from three contexts:
sendmsg() claiming and progressing a transfer, the RX path consuming
Flow Control/echo frames, and two hrtimers timing out a stalled
transfer. Mixing a lock-free cmpxchg() claim in sendmsg() with
hrtimer_cancel() calls made under so->rx_lock elsewhere left windows
where a frame or timer callback could act on a state that had already
moved on, corrupting an unrelated transfer.

so->rx_lock now covers the full lifecycle of a TX claim: sendmsg()
takes it to check so->tx.state is ISOTP_IDLE, switch it to
ISOTP_SENDING, bump so->tx_gen and drain the previous transfer's
timers - all as one critical section. isotp_rcv_fc()/isotp_rcv_cf()
already run under this lock via isotp_rcv(), and isotp_rcv_echo() now
takes it itself, so none of them can ever observe a transfer mid-claim.
This also means a transfer can no longer be handed to sendmsg()'s
cleanup paths (signal or send error) while another thread is
concurrently claiming or finishing it, so those paths can cancel
timers and reset the state unconditionally.

isotp_release() claims the socket the same way, so a racing sendmsg()
sees a consistent ISOTP_SHUTDOWN and skips arming its timer or sending.

Only the hrtimer callbacks stay outside so->rx_lock, since they run
under so->rx_lock's cancellation elsewhere and taking it themselves
would deadlock. so->tx_gen lets them recognize whether the transfer
they timed out is still the one currently active, so they don't
report an error against a transfer that has since completed or been
superseded.

Fixes: e057dd3 ("can: add ISO 15765-2:2016 transport protocol")
Reported-by: sashiko-bot@kernel.org
Closes: https://lore.kernel.org/linux-can/20260710142146.BDAE61F000E9@smtp.kernel.org/
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://patch.msgid.link/20260712-isotp-fixes-v10-3-793a1b1ce17f@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=0b05eca9589f609e2491b528dccf683168a4cda8

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

The original Linux kernel CVE announcement for CVE-2026-72124 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72124

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:N/I:L/A:L
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H
  The Best / paranoid CVSS score: 5.9

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: 2
  Paranoid ActionableScore: 3

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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).