From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98420][MODERATE 7.0] ksmbd: follow SMB2 session expiration semantics [ Upstream Date: Wed, 14 Oct 2026 22:19:14 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98420 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 4 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: c99ea7855124ca1428a1e59c2b4590aaef34eacf List-Id: CVE: CVE-2026-98420 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: ksmbd: follow SMB2 session expiration semantics [ Upstream Commit: c99ea7855124ca1428a1e59c2b4590aaef34eacf Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c99ea7855124ca1428a1e59c2b4590aaef34eacf Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98420 Analysis date: Wed, 14 Oct 2026 22:19:14 -0400 ActionableScore: 4 ActionableScore lower bound: unknown 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-2026-98420 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98420 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-2026-98420 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98420 CHECK WITH IMPACT FROM ORIG NN NONE | AEGIS IMPACT MODERATE AEGIS_AS=3 LEGACY=MODERATE_KPANIC RESULT=DIFF (independent Legacy and Aegis differ; FINAL: MODERATE_KPANIC, Aegis: MODERATE) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';**CWE-400;CWE-770;CWE-613;*CWE-664;Other CVSS 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '7.5';DESCR 'ksmbd can apply incorrect SMB2 session expiration semantics and destroy a valid session after a period of inactivity when another SessionSetup exchange starts on the same connection. This invalidates associated tree connections and can make mapped drives fail with STATUS_NETWORK_NAME_DELETED. The affected session lifecycle also permits abandoned authentication exchanges or incomplete setup connections to retain server resources until they are explicitly removed. Repeated unauthenticated connections can therefore create a network resource exhaustion risk. For the CVSS the PR:N value is selected because a remote client can initiate SMB negotiation and SessionSetup activity without first completing authentication. The issue is network reachable when ksmbd is enabled and its SMB service is accessible to the attacker. Impact is limited to availability based on the analyzed code. The demonstrated effects are session disruption and resource exhaustion with no concrete UAF OOB access information disclosure or write primitive. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 7.5 and the production ActionableScore returned 4 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage LOW to MODERATE_KPANIC because the ActionableScore threshold rule was applied. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4. The independent weaker Aegis shadow evaluated CVSS 7.5 and ActionableScore 3 with primitive class CLASS_C and manual review RECOMMENDED. Its independently reconciled impact was MODERATE. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) MAYBE REMOTE DISK INIT RACE SKIP LINUS KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES RequiresHostUID0=NO AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw conservative score: 4 * Conservative score: 4 * Raw paranoid score: 4 * Paranoid score: 4 * No floor or cap applied. * Final recommended bucket: **Borderline / manual review recommended**:: 2. Signal breakdown * +2 Remote reachability. An unauthenticated network client can initiate SMB negotiation and SessionSetup activity against an exposed ksmbd service. * +1 Availability impact. Incorrect expiration can destroy a valid session, invalidate its tree connections, and cause mapped drives to fail with STATUS_NETWORK_NAME_DELETED. * +1 Resource-exhaustion concern. The commit explicitly identifies abandoned SessionId-zero exchanges and incomplete connections as an unauthenticated memory-exhaustion path. This is independent of established-session invalidation. * +0 No persistent-reference-leak bonus. Resources are retained by incomplete live connections or sessions, but the evidence does not establish an unrecoverable missing reference release surviving connection cleanup. * +0 No crash bonus. Kernel panic or host-wide fatal failure is not demonstrated. * +0 No corruption bonus. No UAF, OOB access, double release, arbitrary write, stale post-lifetime access, or controlled kernel-memory corruption is established. * +0 No authorization-bypass signal. The defect confuses session inactivity with credential expiration but does not turn a mandatory access-control DENY into ALLOW. * +0 No confidentiality or integrity signal. The demonstrated effects are session disruption and resource consumption. * +0 B5-R does not apply because there is no heap OOB write or retry-accumulated corrupted-state consumption. * +0 B3-PENDING does not apply because no shared-backing or file-backed write is present. * +0 B4-PENDING does not apply because no authorization guard is omitted or bypassed. * No negative privilege penalty. The resource-exhaustion path is explicitly unauthenticated. * No paranoid increase. Host-wide exhaustion is possible under sustained abuse, but no concrete isolation bypass, persistent leak, kernel crash, or stronger primitive supports an additional point. 3. Reachability analysis The relevant attacker is a remote unauthenticated SMB client. It can open connections, begin negotiation or SessionSetup, and abandon incomplete authentication state. A client with an established session can also encounter erroneous deletion when another SessionSetup exchange starts on the same connection. No host UID 0, capability, user namespace, or network-namespace privilege is required after ksmbd has been enabled and exposed. Enabling and configuring the server is prior administrator setup, but it is not an attacker privilege required for the complete network trigger. The ordinary TCP path requires no special hardware. SMB Direct requires RDMA, but that is not needed for the TCP exposure. No race or narrow timing condition is established. 4. Primitive and severity interpretation The exact primitive is incorrect SMB session-lifecycle handling combined with insufficient bounding of incomplete unauthenticated connection and authentication state. It is an invalid-state and resource-exhaustion issue, not a memory-lifetime violation. There is no stale post-free object use, repeated release, refcount mutation, or active structured-object corruption. The demonstrated consequences are deletion of valid sessions, loss of tree connections, mapped-drive failures, and accumulation of resources through abandoned setup activity. PrimitiveClass is CLASS_C because the behavior is availability-oriented and no independently useful corruption or authorization primitive is established. ImportantCandidate is NO because neither memory corruption nor a security-boundary violation is present. AutoDowngradeAllowed is YES because the unresolved risk remains network DoS and service disruption rather than an Important-preserving primitive. Operationally, this is a network-reachable Moderate issue that merits review when ksmbd is exposed to untrusted networks, but the supplied evidence does not support Important-class treatment. 5. One-sentence report phrase A remote unauthenticated client can retain ksmbd setup resources through abandoned SMB authentication activity, while incorrect session expiration can also invalidate established tree connections and disrupt mapped drives. 6. Manual review recommendation MANUAL CHECK RECOMMENDED The issue is remotely reachable before authentication and includes an explicitly identified memory-exhaustion path, but no corruption, authorization bypass, or Important-preserving primitive is established. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ksmbd: follow SMB2 session expiration semantics [ Upstream Commit: c99ea7855124ca1428a1e59c2b4590aaef34eacf Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c99ea7855124ca1428a1e59c2b4590aaef34eacf Changed files: fs/smb/server/connection.c fs/smb/server/connection.h fs/smb/server/mgmt/user_session.c fs/smb/server/mgmt/user_session.h fs/smb/server/proc.c fs/smb/server/server.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=c99ea7855124ca1428a1e59c2b4590aaef34eacf ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98420 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98420 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:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 7.5 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: 4 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).