* [CVE-2026-98377][MODERATE 7.0] vlan: require the MAC header to be present in __vlan_insert_inner_tag() [ Upstream
@ 2026-10-10 2:11 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-10-10 2:11 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98377
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: vlan: require the MAC header to be present in __vlan_insert_inner_tag() [ Upstream
Commit: 40a5cc4b7251c74f3341332a226d02200e96bccf
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=40a5cc4b7251c74f3341332a226d02200e96bccf
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98377
Analysis date: Fri, 09 Oct 2026 22:11:50 -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-2026-98377 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98377
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-2026-98377 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98377 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE_KPANIC RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both MODERATE_KPANIC) 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:N';CWE-125;*CWE-200;CWE-908;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '5.5';DESCR 'A kernel information disclosure occurs because __vlan_insert_inner_tag() can rewrite an ETH_HLEN MAC header without first ensuring that mac_len bytes are present in the skb. With an IFF_TUN device whose hard_header_len is zero, a local process can submit a one byte AF_PACKET SOCK_RAW frame and apply additional VLAN push operations. The helper then moves bytes located beyond skb tail into the transmitted frame, exposing uninitialized slab data and potentially kernel address material. For the CVSS the PR:L value is used because triggering requires a local process with access to a raw packet socket and normally CAP_NET_RAW, while TUN or traffic control configuration may also require delegated CAP_NET_ADMIN. The issue is not remotely triggered by received network traffic, although disclosed bytes can be transmitted onto the adjacent layer two network. Impact is a kernel confidentiality breach and possible KASLR weakening. No out of bounds write, kernel crash, or direct privilege escalation primitive is demonstrated.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE OOB BPF SKB HARDWARE LINUS PACKET KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 5
* Paranoid score: 5
* No floor or cap was applied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
* +2 Strong disclosure primitive. A short skb causes bytes beyond skb tail to be copied into a transmitted frame. The demonstrated output includes 11 bytes of uninitialized slab data and linear-map address material.
* +1 Confidentiality plausible. Kernel slab contents are directly exposed through attacker-observable packet output.
* +1 Practical exploit chain. The supplied evidence connects a one-byte AF_PACKET frame and repeated VLAN pushes to a concrete transmitted disclosure.
* +1 Common networking packet-processing path. The defect is in the shared VLAN skb insertion helper used from generic transmit, traffic-control, and BPF-related paths.
* No privilege penalty. Host-admin-equivalent privilege is not positively established, while complete below-host-admin namespace reachability is also not established.
* No remote-reachability bonus. Incoming remote traffic is not shown to initiate the vulnerable sequence.
* No OOB-write bonus. The helper performs in-bounds stores after moving unavailable source bytes. The security primitive is disclosure from a logical over-read, not an overwrite beyond allocated storage.
* No arbitrary read, arbitrary write, controlled target, UAF, kernel crash, or LPE is established.
* B5-R does not apply because there is no confirmed heap OOB write or later consumption of corrupted structured state.
* B3-PENDING does not apply because no shared or file-backed storage modification is established.
* B4-PENDING does not apply because no authorization decision changes from DENY to ALLOW.
3. Reachability analysis
A local process must construct a short AF_PACKET SOCK_RAW frame on an IFF_TUN device and cause additional VLAN push processing through clsact or BPF. AF_PACKET access normally requires CAP_NET_RAW. TUN and traffic-control configuration can require CAP_NET_ADMIN, while the BPF alternative has separate loading and attachment restrictions.
Numeric host UID 0 is not intrinsically required because Linux capability checks can authorize these operations independently of UID. However, the supplied evidence does not establish whether every required stage is available in an attacker-created user and network namespace on the evaluated system. Therefore HostAdminRequired and NamespaceScopedPrivilege remain UNKNOWN.
No special physical hardware or race is required. The operation sequence is deterministic once the necessary packet, device, and VLAN-processing access exists. The bug is not directly triggered by received network traffic, although disclosed bytes can be emitted onto an adjacent network.
4. Primitive and severity interpretation
The exact primitive is an attacker-visible logical out-of-bounds read of uninitialized skb slab data. The vulnerable memmove reads source bytes beyond skb tail but within the allocated skb head and copies them into the outgoing frame. Repeated VLAN pushes increase the exposed portion, and the demonstrated frame contains kernel linear-map address material.
This is not a UAF, lifetime violation, shared-backing write, authorization bypass, or corrupted-state-consumption case. It is CLASS_A because a concrete kernel disclosure reaches attacker-visible output and can reveal address material useful for weakening KASLR. The demonstrated consequence is confidentiality loss. Further arbitrary kernel reads, memory modification, host compromise, and privilege escalation remain speculative.
ImportantCandidate is YES because automatically downgrading a repeatable kernel slab and address disclosure could discard meaningful exploit-chain value. AutoDowngradeAllowed is NO for the same reason, although the evidence does not independently prove Important-grade privilege escalation.
5. One-sentence report phrase
A crafted short AF_PACKET frame followed by repeated VLAN pushes can copy uninitialized skb slab bytes, including kernel address material, into a transmitted packet and therefore requires manual security review.
6. Manual review recommendation
MANUAL CHECK REQUIRED
The disclosure is concrete and attacker-visible, while the complete capability and namespace boundary and the amount of repeatable kernel memory exposure require product-specific validation.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: vlan: require the MAC header to be present in __vlan_insert_inner_tag() [ Upstream
Commit: 40a5cc4b7251c74f3341332a226d02200e96bccf
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=40a5cc4b7251c74f3341332a226d02200e96bccf
Changed files:
include/linux/if_vlan.h
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=40a5cc4b7251c74f3341332a226d02200e96bccf
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98377 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98377
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:N
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
The Best / paranoid CVSS score: 5.5
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: 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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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