* [CVE-2026-98301][MODERATE REGULAR] net: bridge: mst: move switchdev call outside rcu [ Upstream
@ 2026-10-11 3:42 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-11 3:42 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98301
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net: bridge: mst: move switchdev call outside rcu [ Upstream
Commit: b9661fd2423fc25e91e0517ecc0b6156ad83e3a8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b9661fd2423fc25e91e0517ecc0b6156ad83e3a8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98301
Analysis date: Sat, 10 Oct 2026 23:42:06 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
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-2026-98301 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98301
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-2026-98301 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98301 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=MODERATE RESULT=DIFF (independent Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-667;*CWE-833;CWE-821;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'br_mst_set_state can invoke the blocking switchdev notifier chain while holding rcu_read_lock. A notifier callback that sleeps can violate the RCU read side execution rules and may cause a sleeping while atomic warning, a prolonged stall, or a driver dependent deadlock. The trigger is a local netlink control plane operation that changes a nonzero MSTI state while RTNL is held. It is not directly reachable through ordinary remote packet traffic. For the CVSS the PR:L in the paranoid score reflects environments where CAP_NET_ADMIN is delegated to a network service, container root, or a user in a network namespace rather than requiring unrestricted host root. Impact is primarily denial of service. No UAF, OOB access, information leak, or write primitive is demonstrated by this patch. Manual review is appropriate because the final availability impact depends on the switchdev or DSA notifier implementation and the affected hardware configuration.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) MAYBE LOCK DANGER UAF IMPROVEONLY LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 potential strong DoS: a blocking switchdev notifier is invoked inside an RCU read-side critical section. A sleeping callback can produce a warning, prolonged RCU stall, or driver-dependent deadlock.
* No remote-reachability point: ordinary packet traffic does not reach this control-plane operation.
* No local-unprivileged point: authorization to change the nonzero MSTI state is not established below host administration.
* No UAF or corruption point: the current patch establishes neither stale post-lifetime access nor OOB access, overwrite, double release, or refcount corruption.
* No extra availability point: a persistent or independent effect beyond the possible stall or deadlock is not demonstrated.
* No C or I points: there is no disclosure, unauthorized modification, or security-boundary bypass.
* B5-R and B3-PENDING do not apply. No retry-accumulated OOB write or shared-backing write exists.
* B4-PENDING does not apply. No authorization decision changes from DENY to ALLOW.
3. Reachability analysis
The trigger is a netlink control-plane request changing a nonzero bridge MSTI while RTNL is held. The exact capability check and namespace governing the complete operation are not supplied. CAP_NET_ADMIN is normally relevant, but the evidence does not establish whether an attacker-created namespace is sufficient for the complete switchdev or DSA path.
Numeric host UID 0 is not inherently required because netlink administration is capability based. Effective host-admin requirements remain unknown because the affected topology may involve a host-owned bridge port, DSA device, or hardware-offloaded switch. Such a topology requires prior configuration, but the supplied evidence does not establish whether it must always be provisioned by a separate host administrator.
This is not a timing race. The invalid context occurs synchronously when a relevant blocking notifier callback is invoked. The practical consequence depends on the registered switchdev callback and kernel configuration.
4. Primitive and severity interpretation
The exact primitive is execution of a potentially sleeping blocking-notifier callback while `rcu_read_lock()` is held. This is a synchronization-context violation classified as CLASS_C because the supported effects are warning, stall, or possible deadlock rather than an independently useful corruption primitive.
There is no active structured-object UAF, fixed stale storage, repeated release, stale refcount mutation, or authorization bypass. The `Fixes` reference to an earlier VLAN use-after-free fix does not establish a UAF in this follow-up defect.
The demonstrated root cause supports availability concern only. Memory corruption, information disclosure, privilege escalation, and attacker-controlled state replacement are unsupported. ImportantCandidate is therefore NO, and automatic downgrade is allowed. Manual review remains recommended to determine whether a specific switchdev or DSA notifier can produce a host-wide deadlock instead of a nonfatal warning.
5. One-sentence report phrase
A local bridge MST netlink update can invoke a sleeping switchdev notifier inside an RCU read-side critical section, potentially causing a warning, prolonged stall, or driver-dependent denial of service without establishing memory corruption.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Confirm the affected switchdev or DSA notifier behavior and whether the complete trigger requires host-admin control or can operate through delegated namespace-scoped CAP_NET_ADMIN.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: net: bridge: mst: move switchdev call outside rcu [ Upstream
Commit: b9661fd2423fc25e91e0517ecc0b6156ad83e3a8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b9661fd2423fc25e91e0517ecc0b6156ad83e3a8
Changed files:
net/bridge/br_mst.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=b9661fd2423fc25e91e0517ecc0b6156ad83e3a8
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98301 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98301
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:H/UI:N/S:U/C:N/I:N/A:L
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 4.7
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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