[CVE-2026-80707][MODERATE REGULAR] can: j1939: transport: j1939_session_fresh_new(): initialize receive buffer

[CVE-2026-80707][MODERATE REGULAR] can: j1939: transport: j1939_session_fresh_new(): initialize receive buffer

[AL-KERNEL]

CVE: CVE-2026-80707
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: can: j1939: transport: j1939_session_fresh_new(): initialize receive buffer
Commit: 348818277a3646d5b9fa60c9d20c00dc4bc86832
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=348818277a3646d5b9fa60c9d20c00dc4bc86832
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80707
Analysis date: Fri, 28 Aug 2026 05:26:22 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline manual review recommended / Actionable Moderate at minimum
Manual review required: YES

Summary:
A J1939 transport receive buffer was allocated without zero initialization, allowing a CAN/J1939 peer to potentially observe residual kernel heap data through the receive path on systems where the J1939 bus is reachable.

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

The original Linux kernel CVE announcement for CVE-2026-80707 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80707

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.

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

CVE-2026-80707	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N';CWE-908;*CWE-457;*CWE-200;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '6.5';DESCR 'J1939 transport receive buffers were allocated with skb_put without zero initialization, so residual kernel heap bytes could remain in the skb data area before protocol reassembly overwrites it. A peer with access to the CAN/J1939 segment may be able to influence receive session creation and expose uninitialized buffer contents through the J1939 receive path. For the CVSS the PR:N is used for the adjacent network case because no local account on the victim is required when the attacker can send crafted J1939 traffic on the CAN bus. The issue is not Internet-routable in the usual sense and is more realistic on local vehicle, industrial, or embedded CAN networks. Impact is primarily confidentiality loss from possible kernel memory disclosure, with no direct evidence of integrity impact, denial of service, or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / Actionable Moderate at minimum (with actual score 4)	YES	SIMPLEFIX SKB LINUS  INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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

ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: **3**
* Paranoid score: **4**
* Final recommended bucket: **Borderline manual review recommended / Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* **Remote reachable / network-triggerable: +2**
  The trigger is not Internet-routable in the normal IP sense, but a peer on the CAN/J1939 segment can plausibly influence J1939 transport session creation.

* **Confidentiality impact plausible: +1**
  The patch changes `skb_put()` to `skb_put_zero()`, and the commit explicitly says the receive buffer may contain residual data. This supports a possible uninitialized kernel memory disclosure.

* **Networking packet-processing path: +1**
  The affected code is in `net/can/j1939/transport.c` and handles J1939 transport receive session buffers.

* **Rare and difficult-to-reach subsystem/configuration: -1**
  J1939 requires CAN/J1939 support and access to the relevant CAN bus or gateway. This is typically vehicle, industrial, embedded, or lab-network exposure rather than broad Internet exposure.

Paranoid adjustment:

* In deployments where CAN/J1939 is a real exposed control or storage network, the rarity penalty may be inappropriate. That gives the paranoid score **4**.

Not triggered:

* No UAF, double free, OOB write, refcount takeover, callback corruption, or type confusion is shown.
* No integrity impact is demonstrated.
* No reliable kernel crash or privilege escalation path is demonstrated.

## 3. Reachability analysis

A remote peer on the same CAN/J1939 segment may be able to trigger allocation of a J1939 receive buffer and influence transport reassembly behavior. No local account on the victim is required for the adjacent-network interpretation, so PR is effectively **PR:N** in CVSS terms when the attacker can send J1939 traffic on the CAN bus.

This is not normally reachable from the public Internet. Practical exploitation usually requires access to a local CAN/J1939 network, a vehicle or industrial bus, or a gateway that forwards attacker-controlled J1939 frames. Namespaces and containers are less central for the adjacent-network case, but a local attacker with AF_CAN access could also be relevant depending on system policy.

Call-site confidence: **medium**. The patch and commit clearly show uninitialized receive-buffer risk, but the supplied context does not fully show every delivery path that would determine how much residual data can actually be observed.

## 4. Severity interpretation

This behaves like an **actionable information disclosure candidate**, not like a generic crash-only Moderate and not like an Important memory-corruption issue. The realistic impact is potential leakage of residual kernel heap data through J1939 receive-buffer handling.

The theoretical worst case is higher confidentiality impact if sensitive kernel data can survive in the reused buffer and become visible to an attacker. However, the patch does not support privilege escalation, arbitrary write, UAF exploitation, or integrity impact.

## 5. One-sentence report phrase

A J1939 transport receive buffer was allocated without zero initialization, allowing a CAN/J1939 peer to potentially observe residual kernel heap data through the receive path on systems where the J1939 bus is reachable.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED. YES REQUIRES MANUAL CHECK.**

Reason: this is a potential kernel memory disclosure reachable from an adjacent network protocol path. Manual review should confirm whether normal and abnormal J1939 reassembly paths can expose bytes that were not overwritten by received payload data.

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

Patch: can: j1939: transport: j1939_session_fresh_new(): initialize receive buffer
Commit: 348818277a3646d5b9fa60c9d20c00dc4bc86832
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=348818277a3646d5b9fa60c9d20c00dc4bc86832

Commit description:

Zero the allocated buffer in j1939_session_fresh_new() to ensure it
contains no residual data.

While there is a potential performance impact if users allocate maximum
sized ETP buffers, most real-world use cases are not noticeably affected
since the maximum known buffer size is typically around 65K.

Fixes: 9d71dd0 ("can: add support of SAE J1939 protocol")
Reported-by: Ji'an Zhou <eilaimemedsnaimel@gmail.com>
Message-ID: <CAPAUci5dykCLjoijqkUtFqJFesgncrD7+S6y_V=gjbFkY2Tifg@mail.gmail.com>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://patch.msgid.link/20260728055835.1151785-3-o.rempel@pengutronix.de
Cc: stable@kernel.org
[mkl: add Message-ID]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/can/j1939/transport.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=348818277a3646d5b9fa60c9d20c00dc4bc86832

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

The original Linux kernel CVE announcement for CVE-2026-80707 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80707

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:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
  The Best / paranoid CVSS score: 6.5

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: 4

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).