[CVE-2026-72114][MODERATE 7.0] can: bcm: validate frame length in bcm_rx_setup() for RTR replies

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

CVE: CVE-2026-72114
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: can: bcm: validate frame length in bcm_rx_setup() for RTR replies
Commit: 7d966cdee006911d3957e1a4e72cb93c39cd8c1e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7d966cdee006911d3957e1a4e72cb93c39cd8c1e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72114
Analysis date: Sat, 15 Aug 2026 05:08:50 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A CAN BCM RX_SETUP RTR reply frame could be installed with an invalid CAN or CAN FD length and later transmitted by bcm_can_tx(), creating a local malformed-frame/OOB-read style condition with possible kernel memory disclosure or crash impact.

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

The original Linux kernel CVE announcement for CVE-2026-72114 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72114

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.

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

CVE-2026-72114	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H';*CWE-20;CWE-1284;CWE-125;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:L';BEST CVSS score: '7.1';DESCR 'A length validation bug in CAN BCM allows an RX_SETUP RTR reply frame to be installed with a CAN or CAN FD payload length larger than the protocol limit. The frame can later be transmitted by bcm_can_tx when a matching remote request is received, so the kernel and the CAN driver may process a frame whose len field is inconsistent with the stored frame buffer. For the CVSS the PR:L is used because reliable triggering requires a local user or process that can create a CAN BCM socket and configure RX_SETUP. The issue is not directly reachable from an IP network. A CAN bus peer may only provide the RTR stimulus after the malformed local BCM state already exists. Impact is at least local denial of service or malformed frame transmission, and in the paranoid case may include kernel memory disclosure or crash due to an out of bounds read style length mismatch.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	LINUS  INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local process can configure CAN BCM RX_SETUP with RX_RTR_FRAME if CAN BCM sockets are available and usable.
* Memory corruption, weak or indirect corruption candidate: +1. The bug installs a frame with an invalid len field, creating a mismatch between the stored CAN/CAN FD frame buffer and the length later consumed by bcm_can_tx().
* Confidentiality impact plausible: +1. The most concerning primitive is an OOB read style length mismatch when transmitting a stored frame, which may expose adjacent kernel memory into the generated CAN frame.

Paranoid additional signals:

* Reliable kernel crash / strong DoS: +1. Invalid frame length may be consumed by CAN transmit paths or drivers and can plausibly cause malformed skb handling, warnings, or crash conditions.
* Local high-control kernel data-plane API concern: +1. CAN BCM lets a local process install persistent kernel-side frame state that is later used asynchronously in response to RTR traffic.

Not counted:

* Remote reachable: +0. This is not directly reachable from an IP network.
* Strong LPE plausibility: +0. The patch supports an invalid length / possible OOB read style issue, not UAF reclaim, arbitrary write, type confusion, or controlled overwrite.
* Strong generic memory corruption: +0. No OOB write, double free, UAF, refcount takeover, or attacker-controlled overwrite is shown.
* Rare subsystem penalty: 0. CAN is deployment-specific, but CAN BCM is reachable through a normal local socket interface where CAN is enabled.

## 3. Reachability analysis

The reliable trigger requires a local user or process that can create a CAN BCM socket and configure RX_SETUP with RX_RTR_FRAME. A CAN bus peer can provide the matching RTR request that causes the stored reply frame to be transmitted, but the malformed BCM operation must already have been installed locally. Network namespaces may matter if CAN interfaces or vcan devices are delegated into containers, but creating or managing CAN interfaces usually depends on host configuration and CAP_NET_ADMIN. The path is not Internet-facing and is mainly relevant on systems with CAN or vcan enabled.

Call-site confidence: high, because the patch shows both validation and the later intended use path comment for bcm_can_tx().

## 4. Severity interpretation

This behaves above ordinary Low because it is not just a cosmetic validation fix: an invalid user-controlled frame length can persist in kernel BCM state and later be consumed by the transmit path. Realistic evidence supports local DoS or limited kernel memory disclosure concerns, while privilege escalation remains speculative. The conservative interpretation is Borderline Moderate, but the paranoid score reaches Actionable Moderate because the issue involves a kernel networking transmit path with an OOB read style length mismatch.

## 5. One-sentence report phrase

A CAN BCM RX_SETUP RTR reply frame could be installed with an invalid CAN or CAN FD length and later transmitted by bcm_can_tx(), creating a local malformed-frame/OOB-read style condition with possible kernel memory disclosure or crash impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Manual review is required because the bug crosses from input validation into persistent kernel transmit state, and the downstream impact depends on how bcm_can_tx(), skb construction, CAN core helpers, and device drivers consume the invalid len field.

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

Patch: can: bcm: validate frame length in bcm_rx_setup() for RTR replies
Commit: 7d966cdee006911d3957e1a4e72cb93c39cd8c1e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7d966cdee006911d3957e1a4e72cb93c39cd8c1e

Commit description:

bcm_tx_setup() validates cf->len against the CAN/CAN FD DLC limits
before installing frames for TX_SETUP, but bcm_rx_setup() never did
the same for the RTR-reply frame configured via RX_SETUP with
RX_RTR_FRAME.

Fixes: ffd980f ("[CAN]: Add broadcast manager (bcm) protocol")
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://patch.msgid.link/20260714-bcm_fixes-v15-7-562f7e3e42da@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/bcm.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=7d966cdee006911d3957e1a4e72cb93c39cd8c1e

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

The original Linux kernel CVE announcement for CVE-2026-72114 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72114

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:L/PR:L/UI:N/S:U/C:L/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
  The Best / paranoid CVSS score: 7.1

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: 3
  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: NO
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).