[CVE-2026-97612][MODERATE 7.0] net: mpls: clear inner_protocol when the last label is popped

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

CVE: CVE-2026-97612
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: net: mpls: clear inner_protocol when the last label is popped
Commit: 011e17b5cae19b9f6a150923275e41c278de64f0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=011e17b5cae19b9f6a150923275e41c278de64f0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97612
Analysis date: Fri, 25 Sep 2026 10:31:18 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-97612 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97612

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-2026-97612	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97612 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:H/A:H';*CWE-787;CWE-195;CWE-681;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';BEST CVSS score: '7.8';DESCR 'A stale MPLS inner network header can survive after the last MPLS label is popped. Open vSwitch can later reuse this stale header after MPLS recirculation and fragmentation, causing a negative network offset to pass a signed bounds check. The negative value is converted to an unsigned length and used by memcpy in prepare_frag, resulting in a massive kernel out of bounds write. For the CVSS the PR:L because reliable triggering requires control of Open vSwitch flow configuration or equivalent delegated network administration capabilities. The issue is not directly network reachable through packet traffic alone, although a remote peer may supply packets after a privileged actor has installed a vulnerable MPLS flow configuration. Impact includes kernel crash and may include confidentiality integrity and privilege escalation consequences because the patch context demonstrates an out of bounds kernel write. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	YES	REMOTE KASAN SKB HARDWARE LINUS IPV6 KPANIC PACKET  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	NO	NO	checked

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

ActionableScore=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 5
* Raw paranoid score: 4
* Paranoid score: 5
* Applied conservative floor: 4 -> 5. A concrete attacker-influenced kernel out of bounds write must not be automatically closed as ordinary Moderate.
* Applied paranoid floor: 4 -> 5.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 Strong kernel corruption primitive. A stale inner_network_header creates a negative skb_network_offset. The signed bounds check accepts the negative value, which is widened to unsigned int and passed as hlen to memcpy. The resulting approximately 4 GiB copy writes beyond the small per CPU l2_data buffer.
* +1 Reliable kernel crash or strong DoS. The supplied reproducer shows a supervisor kernel page fault in memcpy through prepare_frag and ovs_fragment.
* +1 Integrity plausible. The vulnerable operation is a real kernel write past the intended destination buffer. The exact overwritten objects and useful post corruption state are not established.
* Controlled reclaim, arbitrary kernel read write, controlled target selection, callback control, credential corruption, information disclosure, and demonstrated privilege escalation are not established.
* Direct remote reachability is not awarded. A remote packet alone does not establish the complete sequence because the MPLS push pop recirculation and fragmentation action path requires a relevant Open vSwitch flow configuration.
* Local unprivileged trigger is not awarded. The supplied material does not establish that an ordinary unprivileged user can create the necessary Open vSwitch MPLS action configuration.
* No host admin penalty is applied. The supplied evidence suggests network administration or Open vSwitch control plane access is relevant, but it does not prove that host admin equivalent privilege is required for every deployment.
* No niche subsystem penalty is applied. Open vSwitch MPLS configuration is specialized, but no evidence proves that an attacker cannot reach it in an evaluated deployment.
* No extra Availability point is awarded. The demonstrated Oops is already counted as the reliable kernel crash signal.
* No paranoid bonus is awarded. The concrete out of bounds write is serious, but the available evidence does not establish a distinct controlled reclaim, target selection, or post corruption exploitation primitive beyond the same overwrite.

3. Reachability analysis

The direct trigger is an Open vSwitch datapath sequence involving MPLS push, removal of all labels, recirculation, another MPLS push, and the OVS fragmentation path. The attacker must be able to cause packets to execute a matching vulnerable OVS action graph and reach ovs_fragment.

The supplied evidence supports that packet contents can reach the copy source and that the malformed state produces the negative length. It does not establish who can install or modify the required OVS flows. In common host deployments, configuring OVS flows and MPLS actions is performed by an administrator or a delegated network management component. However, the exact capability checks and whether all required stages can be completed from an attacker controlled network namespace are not supplied.

HostAdminRequired is therefore UNKNOWN. NamespaceScopedPrivilege is also UNKNOWN. The existence of network namespaces or potentially delegated CAP_NET_ADMIN would not by itself prove that the complete OVS configuration and vulnerable execution path is namespace scoped.

This is not directly remote reachable in the strict sense because untrusted network traffic requires prior vulnerable local control plane configuration. A remote peer may nevertheless provide packet data after a privileged or delegated actor has installed the relevant OVS MPLS actions.

4. Primitive and severity interpretation

The exact primitive is an attacker influenced out of bounds kernel write caused by signed to unsigned conversion of a stale negative skb header offset. The stale inner header metadata is not a use after free. It is stale protocol state that is later trusted by ovs_fragment.

The memcpy destination starts at a small per CPU l2_data buffer, while the derived length can become approximately 4 GiB. The supplied trace confirms an attempted supervisor mode write in memcpy with RDX equal to 0xfffffff8. This is stronger than a NULL pointer dereference or crash only invalid state.

The write target begins at a fixed kernel buffer and the supplied evidence does not show controlled placement, a chosen final target, controlled object replacement, callback dispatch, arbitrary read write, or a demonstrated LPE chain. Therefore, this is CLASS_A due to a concrete attacker influenced OOB write, but it is not scored as a demonstrated arbitrary kernel write or demonstrated privilege escalation.

ImportantCandidate is YES because a concrete kernel memory corruption primitive exists and the practical reachability and post corruption leverage require manual investigation. AutoDowngradeAllowed is NO because automatically treating the bug as only an OVS crash could discard a real out of bounds kernel write primitive.

Likely operational severity is at least actionable Moderate. It can become an Important classification if manual review confirms that a below host admin actor can install the necessary OVS actions, influence packet payloads, and obtain useful corruption of adjacent per CPU state.

5. One-sentence report phrase

A stale MPLS inner header offset can become a negative value that bypasses a signed bounds check and is widened into an approximately 4 GiB memcpy length in the Open vSwitch fragmentation path, causing a kernel out of bounds write and crash.

6. Manual review recommendation

MANUAL CHECK REQUIRED

A concrete kernel out of bounds write is established, but the complete privilege boundary for OVS flow setup and the practical control over the overwritten kernel state are unresolved.

7. Call-site confidence

Call-site confidence: medium

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

Patch: net: mpls: clear inner_protocol when the last label is popped
Commit: 011e17b5cae19b9f6a150923275e41c278de64f0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=011e17b5cae19b9f6a150923275e41c278de64f0

Commit description:

skb_mpls_push() records the pre-encapsulation network header once, gated
on !skb->inner_protocol. skb_mpls_pop() never clears that record, so it
outlives the encapsulation it describes.

Open vSwitch can then re-push MPLS onto a packet whose
inner_network_header still points at the older, deeper offset: push a
label, pop every label, recirculate (ovs_flow_key_update() re-derives
key->eth.type and resets network_header, but leaves inner_*), then push
again. ovs_fragment() trusts the record:

	skb->network_header = skb->inner_network_header;

so skb_network_offset() goes negative. The bound check is signed:

	if (skb_network_offset(skb) > MAX_L2_LEN)

a negative offset passes it, and prepare_frag() widens the value:

	unsigned int hlen = skb_network_offset(skb);
	memcpy(&data->l2_data, skb->data, hlen);

which is a ~4GiB memcpy out of a 30-byte per-CPU buffer.

Reproduced on v7.3-rc1. RDX is the truncated length, (unsigned int)(-8):

  BUG: unable to handle page fault for address: ffffe8ffffc16000
  #PF: supervisor write access in kernel mode
  Oops: 0002 [#1] SMP KASAN NOPTI
  RIP: 0010:memcpy+0x8/0x20
  RDX: 00000000fffffff8 RSI: ffff888105d732db RDI: ffffe8ffffc16000
   prepare_frag+0x3df/0x4e0
   ovs_fragment+0x589/0x7e0
   do_output+0x4ce/0x5e0
   do_execute_actions+0x55d2/0x7b30
   ovs_execute_actions+0xea/0x450

Same root-cause shape as commit 975b5b0 ("ipv6: sr: restore network
header before routing and forwarding"): a stale network header offset
reaching a consumer that widens it. Here it originates in the MPLS
push/pop path.

Clear inner_protocol once the packet is no longer MPLS, so a later push
re-records the current header. net/sched/act_mpls.c is the only other
skb_mpls_pop() caller and gets the same fix; sch_frag.c saves and
restores inner_protocol around fragmentation in the same way OVS does.

Fixes: 48d2ab6 ("net: mpls: Fixups for GSO")
Cc: stable@vger.kernel.org
Signed-off-by: Fourie Zhang <fouriezhang@tencent.com>
Acked-by: Jiri Benc <jbenc@redhat.com>
Link: https://patch.msgid.link/20260902092719.2874481-1-fouriezhang@tencent.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/sched/act_mpls.c
  net/core/skbuff.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=011e17b5cae19b9f6a150923275e41c278de64f0

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

The original Linux kernel CVE announcement for CVE-2026-97612 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97612

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:H/I:H/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: 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: 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).