[CVE-2026-99066][MODERATE REGULAR] can: dev: init_can_skb(): restore skb header initialization

[CVE-2026-99066][MODERATE REGULAR] can: dev: init_can_skb(): restore skb header initialization

[AL-KERNEL]

CVE: CVE-2026-99066
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: can: dev: init_can_skb(): restore skb header initialization
Commit: 8078375dfd0baecd9f1b7b06bb2d6f88d7cb8632
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8078375dfd0baecd9f1b7b06bb2d6f88d7cb8632
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99066
Analysis date: Tue, 27 Oct 2026 01:17:18 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
Malformed CAN skb header initialization can let a received frame drive `packet_rcv_spkt()` into `skb_under_panic()`, causing a host panic without a demonstrated memory-corruption primitive.

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

The original Linux kernel CVE announcement for CVE-2026-99066 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99066

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: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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

CVE-2026-99066	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-99066 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-456;CWE-191;CWE-617;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.5';DESCR 'CAN receive skbs created by alloc_can_skb could retain mac_header as 0xFFFF because init_can_skb no longer reset the skb header offsets. If such an skb reaches packet_rcv_spkt for an active SOCK_PACKET endpoint, the push length calculation can overflow and reach skb_under_panic, causing a kernel BUG and full machine panic. For the CVSS the PR:N value in the paranoid vector reflects an attacker on an adjacent CAN segment who can supply a frame when the victim already has a matching SOCK_PACKET listener. The base case is local with PR:L because creating the packet socket normally requires CAP_NET_RAW or a delegated equivalent. The demonstrated primitive is a checked kernel panic with availability impact only, not an OOB access, UAF, information leak, or privilege escalation. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 6.5 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 6.5 and ActionableScore 2 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	MAYBE	DANGER SIMPLEFIX NETWORK SKB HARDWARE LINUS PACKET  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 1.
* Conservative score: 1; no floor or cap applied.
* Raw paranoid score: 1.
* Paranoid score: 1; adjacent-network bonus withheld because reception requires a pre-existing matching SOCK_PACKET listener.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Reliable kernel crash/strong DoS: `mac_header == 0xFFFF` makes `packet_rcv_spkt()` calculate an overflowing push length, reaching the checked `skb_under_panic()` BUG path and potentially panicking the machine.
* No OOB-write or corruption bonus: the evidence shows bounds detection and panic, not a write beyond skb storage.
* No remote/adjacent +2: a CAN frame can trigger the defect only when privileged local setup has already created a suitable packet-socket listener.
* No privilege penalty: an adjacent sender need not hold host privilege once that listener exists; alternatively, the local setup can use delegated CAP_NET_RAW below host administrator.
* No extra Availability point: it would duplicate the same panic.
* No UAF, controlled write, disclosure, integrity change, authorization bypass, B5-R retry accumulation, B3 shared-backing write, or exploit leverage is shown.

3. Reachability analysis

An adjacent CAN participant can supply the frame when the victim already has a matching SOCK_PACKET endpoint. Creating that endpoint locally normally requires CAP_NET_RAW or a delegated equivalent, but host UID 0 and host-administrator-equivalent power are not required for every grounded trigger model. Whether the complete local setup is available through attacker-created user/net namespaces is not established. No race or unusual hardware timing is shown; a CAN interface and active listener are environmental prerequisites.

4. Primitive and severity reading

The primitive is invalid skb header-offset state consumed by `packet_rcv_spkt()`, producing an underflow/overflow in push-length arithmetic that is caught by `skb_under_panic()`. This is CLASS_C checked crash behavior, not an actual heap OOB write, stale-object use, or active-state corruption. The shown effect is host availability loss; non-crash exploitation is unsupported. ImportantCandidate is therefore NO, and auto-downgrade remains allowed.

5. One-sentence report phrase

Malformed CAN skb header initialization can let a received frame drive `packet_rcv_spkt()` into `skb_under_panic()`, causing a host panic without a demonstrated memory-corruption primitive.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm product exposure to CAN plus legacy SOCK_PACKET listeners and whether delegated CAP_NET_RAW materially broadens local reachability.

7. Call-site confidence

Call-site confidence: high

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

Patch: can: dev: init_can_skb(): restore skb header initialization
Commit: 8078375dfd0baecd9f1b7b06bb2d6f88d7cb8632
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8078375dfd0baecd9f1b7b06bb2d6f88d7cb8632

Commit description:

Commit 9f10374 ("can: remove private CAN skb headroom infrastructure")
removed the skb_reset_mac_header()/skb_reset_network_header()/
skb_reset_transport_header() calls from init_can_skb(). As a result, RX
skbs from alloc_can_skb() and friends again carry mac_header = 0xFFFF.
When such an skb reaches packet_rcv_spkt() (SOCK_PACKET), the push length
calculation overflows and triggers skb_under_panic -> kernel BUG -> full
machine panic.

The same issue was originally reported in 2014 on linux-can and fixed by
commit 9694390 ("can: add missing initialisations in CAN related
skbuffs"). packet_rcv_spkt() itself has never been hardened: only
packet_rcv() and tpacket_rcv() gained dev_has_header() checks in
commit d549699 ("net/packet: fix packet receive on L3 devices
without visible hard header").

Fixes: 9f10374 ("can: remove private CAN skb headroom infrastructure")
Cc: stable@vger.kernel.org
Reviewed-by: Oliver Hartkopp <socketcan@hartkopp.net>
Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: zjamg <ndaugoing@gmail.com>
Tested-by: Quchaosheng <quchaosheng000406@163.com>
Link: https://patch.msgid.link/20260917123716.63116-1-ndaugoing@gmail.com
Reported-by: Shaunak Datar <shaunakkdatar@gmail.com>
Closes: https://lore.kernel.org/all/20260918151606.765490-1-shaunakkdatar@gmail.com
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/net/can/dev/skb.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=8078375dfd0baecd9f1b7b06bb2d6f88d7cb8632

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

The original Linux kernel CVE announcement for CVE-2026-99066 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99066

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:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  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: unknown
  Paranoid ActionableScore: 1

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).