* [CVE-2026-90114][MODERATE REGULAR] net: bridge: Reject descending VLAN tunnel ranges [ Upstream
@ 2026-09-18 1:19 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-18 1:19 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-90114
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net: bridge: Reject descending VLAN tunnel ranges [ Upstream
Commit: 1181f6bad009408a259bab6aaf0681f11b487972
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1181f6bad009408a259bab6aaf0681f11b487972
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90114
Analysis date: Thu, 17 Sep 2026 21:19:09 -0400
ActionableScore: 3
ActionableScore lower bound: 1
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90114 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90114
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-2026-90114 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-90114 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N';*CWE-20;CWE-681;*CWE-457;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '4.4';DESCR 'A bridge VLAN tunnel range validation bug allows malformed descending VLAN ranges to pass the span check because a negative VLAN delta can be converted during comparison with an unsigned tunnel ID delta. The range loop then performs no iterations and the request return value can depend on an uninitialized err variable, making the netlink operation result unpredictable. For the CVSS the PR:L is used in the higher score because the practical trigger may be available to a user or service with delegated CAP_NET_ADMIN in a network namespace, while full host root is not always required. The issue is not directly network reachable and is triggered through local bridge configuration control plane operations rather than packet traffic. Impact is mainly low integrity impact through incorrect request handling, with a paranoid low confidentiality component only because an uninitialized scalar return value may expose limited state.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 2) YES SIMPLEFIX LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=3
ActionableScoreLower=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 3
* Paranoid score: 3
* Final recommended bucket: **Borderline / manual review recommended**::
No floor or cap changed the conservative score. No floor or cap changed the paranoid score.
2. Signal breakdown
Conservative positive signals:
* +1: malformed local bridge VLAN tunnel netlink input can bypass the intended descending range validation and produce an unpredictable request result due to an uninitialized `err` value.
Paranoid additional signals:
* +1: limited confidentiality concern is defensible because a user-visible return value may depend on an uninitialized kernel stack scalar.
* +1: limited integrity or correctness concern is defensible because malformed input may be reported unpredictably, including possible false success, although no meaningful protected state corruption is shown.
Non-awarded material signals:
* +0: no UAF, double free, OOB write, refcount misuse, list corruption, or active object lifetime violation is established.
* +0: no reliable kernel crash or host-wide DoS is shown.
* +0: no remote packet-processing trigger is established. This is a local bridge configuration control-plane path.
* +0: no arbitrary write, controlled reclaim, callback control, or privilege escalation primitive is demonstrated.
* +0: no concrete authorization bypass is shown. The issue is malformed input handling, not a DENY-to-ALLOW security check bypass.
* +0: no concrete repeated release/refcount operation exists.
* +0: no resource exhaustion or persistent kernel reference leak is established.
Negative signals:
* No host-admin penalty was applied because host-admin-equivalent privilege is not positively established from the supplied text.
* No namespace-scoped privilege assumption was awarded because the complete trigger chain being attacker-reachable inside namespaces is not established.
3. Reachability analysis
The vulnerable path is bridge VLAN tunnel configuration through the netlink control plane. In normal kernel semantics this kind of operation requires CAP_NET_ADMIN for the relevant network namespace, but the supplied evidence does not prove whether the complete operation is limited to host CAP_NET_ADMIN or can be fully performed with attacker-obtainable namespaced CAP_NET_ADMIN.
HostAdminRequired is therefore UNKNOWN. NamespaceScopedPrivilege is also UNKNOWN because the presence of bridge and netlink functionality alone does not prove that all required setup and trigger stages are namespace-scoped and attacker-reachable.
This is not directly network reachable through packet traffic. It requires a local control-plane request that supplies malformed descending VLAN tunnel ranges. No special hardware, firmware, race timing, or boot-only prerequisite is indicated. No timing penalty applies.
4. Primitive and severity interpretation
The exact primitive is an input validation and signedness bug. A descending VLAN range can pass the span comparison because a negative VLAN delta is converted during comparison with an unsigned tunnel ID delta. The later range loop performs no iterations, and the post-loop error check can use an uninitialized `err` value, making the request result unpredictable.
This is not an active structured UAF and not fixed stale storage. There is no cleanup/destructor lifetime issue and no concrete repeated release/refcount operation. The demonstrated consequence is unpredictable control-plane return behavior. The speculative consequence is limited information exposure or low integrity impact from the uninitialized scalar return value, but no kernel memory corruption or privilege escalation path is established.
PrimitiveClass is CLASS_C because the behavior is invalid-state or unpredictable-result behavior without an independently useful corruption primitive. ImportantCandidate is NO because the patch does not establish Class A behavior or meaningful unresolved Class B exploitation leverage. AutoDowngradeAllowed is YES because no concrete memory corruption, security-boundary bypass, repeated lifetime mutation, or strong exploitation primitive would be lost by treating this as low-end triage.
Likely operational severity is Low to low Moderate.
5. One-sentence report phrase
A bridge VLAN tunnel validation bug can let malformed descending ranges pass the span check and leave the request return value dependent on an uninitialized error variable, but exploitation appears limited to local control-plane request confusion or very limited scalar exposure.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Reason: the issue is low severity and auto-downgrade is allowed, but the uninitialized scalar return value and unresolved CAP_NET_ADMIN namespace reachability justify a lightweight manual review before closure.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: net: bridge: Reject descending VLAN tunnel ranges [ Upstream
Commit: 1181f6bad009408a259bab6aaf0681f11b487972
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1181f6bad009408a259bab6aaf0681f11b487972
Changed files:
net/bridge/br_netlink_tunnel.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=1181f6bad009408a259bab6aaf0681f11b487972
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90114 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90114
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:H/UI:N/S:U/C:N/I:L/A:N
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
The Best / paranoid CVSS score: 4.4
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: 1
Paranoid ActionableScore: 3
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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