* [CVE-2026-89776][MODERATE REGULAR] vxlan: vnifilter: enforce exact length of GROUP/GROUP6 attributes [ Upstream
@ 2026-09-16 8:57 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-16 8:57 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-89776
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: vxlan: vnifilter: enforce exact length of GROUP/GROUP6 attributes [ Upstream
Commit: e12c4663529699f457b2988c1dfedf4d13b3b3be
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e12c4663529699f457b2988c1dfedf4d13b3b3be
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89776
Analysis date: Wed, 16 Sep 2026 04:57:23 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89776 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89776
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-2026-89776 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89776 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:L/I:N/A:N';CWE-125;*CWE-200;*CWE-20;BEST CVSS score: '3.3';DESCR 'VXLAN VNI filter netlink validation accepted GROUP and GROUP6 attributes that were shorter than the required IPv4 or IPv6 address size. The later consumer can perform a fixed width address read from the short attribute and copy adjacent uninitialized slab bytes into remote_ip, which can then be observed through RTM_GETTUNNEL. For the CVSS the PR:L is used because triggering requires local access to the rtnetlink control plane and typically CAP_NET_ADMIN in the relevant network namespace, but not full host root in all deployments. The issue is not directly reachable through VXLAN data packets from the network. Impact is limited confidentiality loss from a small kernel memory disclosure, with no evidence of integrity impact, privilege escalation, or denial of service.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) YES OOB SIMPLEFIX NETWORK HARDWARE DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS YES NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
ActionableScoreLower=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=YES
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 1
* Conservative score: 1. No floor or cap applied.
* Raw paranoid score: 2
* Paranoid score: 2. No floor or cap applied.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
Positive signals:
* +1 Confidentiality plausible. The short GROUP/GROUP6 netlink attribute can cause a fixed-width read beyond the supplied payload, and the over-read bytes are stored in remote_ip and observable through RTM_GETTUNNEL.
* +1 paranoid-only local reachability sensitivity. On systems where unprivileged user namespaces are enabled, a local attacker may be able to obtain CAP_NET_ADMIN in an attacker-created network namespace and exercise the VXLAN rtnetlink control plane. This is not used in the conservative score because the product namespace policy is not supplied.
Non-awarded signals:
* No RealUAF. The patch shows a bounded read beyond a short netlink attribute, not stale lifetime use.
* No Class A. The disclosure is small, up to 3 bytes for IPv4 according to the description, and there is no substantial kernel memory disclosure primitive.
* No Class B. There is no kernel memory corruption, lifetime violation, refcount mutation, UAF, or active object replacement.
* No arbitrary write, controlled reclaim, callback control, or privilege escalation is demonstrated.
* No integrity or availability points. The established effect is limited information disclosure, not data modification or crash.
* No direct remote reachability. The trigger is rtnetlink control-plane input, not VXLAN packet data received from the network.
* No host-admin penalty was applied because host-admin-equivalent privilege is not positively established. The relevant operation is normally namespace-scoped CAP_NET_ADMIN over VXLAN netlink configuration.
3. Reachability analysis
The trigger is local control-plane access through rtnetlink to configure VXLAN VNI filter entries. The vulnerable attributes are VXLAN_VNIFILTER_ENTRY_GROUP and VXLAN_VNIFILTER_ENTRY_GROUP6.
The required privilege is CAP_NET_ADMIN for the relevant network namespace. This is not necessarily full host administrator privilege, because VXLAN virtual devices and their netlink configuration are namespace-scoped in normal Linux networking semantics. Therefore HostAdminRequired is NO and NamespaceScopedPrivilege is YES.
Ordinary unprivileged reachability depends on whether the target system allows unprivileged user namespace and network namespace creation. If enabled, a local user may be able to create a namespace, obtain namespace-local CAP_NET_ADMIN, create or configure a VXLAN object, and trigger the vulnerable parser. If disabled, the practical attacker is a delegated network administrator or a process already holding CAP_NET_ADMIN.
No prior privileged setup is required beyond the kernel having VXLAN and VNI filtering support available. No special hardware is required. There is no race and no timing dependency.
4. Primitive and severity interpretation
The exact primitive is a bounded read-only out-of-bounds read from netlink attribute storage caused by accepting shorter-than-required GROUP/GROUP6 payloads. The read data is copied into remote_ip and later exposed through RTM_GETTUNNEL, giving a small kernel memory disclosure.
This is not active structured stale-object use and not fixed stale storage. It is a validation bug leading to a limited information leak. There is no concrete repeated release/refcount operation, no first lifetime operation that may free an object, and no second lifetime mutation through a dangling reference.
PrimitiveClass is CLASS_C because the established primitive is weak and read-only, without independently useful corruption or lifetime leverage. The demonstrated consequence is limited confidentiality impact. The speculative consequence is that leaked bytes might assist another exploit, but no such chain is established here.
ImportantCandidate is NO because the patch supports a small kernel information disclosure only. AutoDowngradeAllowed is YES because there is no unresolved memory corruption, ownership violation, authorization bypass, UAF, or substantial disclosure primitive.
Likely operational severity is Low to ordinary Moderate.
5. One-sentence report phrase
A short VXLAN VNI filter GROUP or GROUP6 netlink attribute can cause a small kernel slab over-read whose bytes are returned via RTM_GETTUNNEL, requiring local rtnetlink control-plane access with CAP_NET_ADMIN in the relevant network namespace and resulting in limited information disclosure only.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Reason: the issue is a real kernel memory disclosure path, but the leak is small, local control-plane triggered, and does not show corruption, DoS, or privilege escalation.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: vxlan: vnifilter: enforce exact length of GROUP/GROUP6 attributes [ Upstream
Commit: e12c4663529699f457b2988c1dfedf4d13b3b3be
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e12c4663529699f457b2988c1dfedf4d13b3b3be
Changed files:
drivers/net/vxlan/vxlan_vnifilter.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=e12c4663529699f457b2988c1dfedf4d13b3b3be
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89776 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89776
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: Not available
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
The Best / paranoid CVSS score: 3.3
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: 2
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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