From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98870][IMPORTANT] ksmbd: remove stale channels from all sessions on teardown [ Upstream Date: Mon, 26 Oct 2026 19:13:32 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98870 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 7 X-AL-KERNEL-ActionableScore-Lower: 6 X-AL-KERNEL-Commit: f8200bb4994e65a2e5c5b314789eeae39078619d List-Id: CVE: CVE-2026-98870 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: NO Patch: ksmbd: remove stale channels from all sessions on teardown [ Upstream Commit: f8200bb4994e65a2e5c5b314789eeae39078619d Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f8200bb4994e65a2e5c5b314789eeae39078619d Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98870 Analysis date: Mon, 26 Oct 2026 19:13:32 -0400 ActionableScore: 7 ActionableScore lower bound: 6 Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: An authenticated remote SMB client can preserve a stale multichannel connection pointer and trigger a later kernel heap use-after-free write during session teardown. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98870 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98870 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: IMPORTANT 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-2026-98870 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-98870 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT IMPORTANT AEGIS_AS=4 LEGACY=IMPORTANT RESULT=SAME (final reconciliation agrees; DECISION: both IMPORTANT) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-459;*CWE-664;Other CVSS 'AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.8';DESCR 'A stale ksmbd multichannel entry can retain a chann conn pointer after the associated ksmbd_conn object has been freed. A later session teardown passes this stale pointer to ksmbd_conn_set_exiting and performs a use after free write into kernel heap memory. The trigger is network reachable through the SMB server and requires a sequence involving session creation, channel binding, a later non binding SESSION_SETUP, and connection teardown. For the CVSS the PR:L value is selected because reliable triggering normally requires an established SMB session and valid SMB multichannel binding, although guest or unusually permissive deployments may reduce the practical authentication barrier. Impact is at least remote denial of service through kernel memory corruption. Reuse of the freed allocation creates a plausible but unproven path to broader confidentiality and integrity impact, so the paranoid score uses C:H I:H A:H. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 8.8 and the production ActionableScore returned 7 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. The independent weaker Aegis shadow evaluated CVSS 5.3 and ActionableScore 4 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was IMPORTANT. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is IMPORTANT.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 7) MAYBE REMOTE WRITE OOB DISK LEAK UAF SKIP - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=7 ActionableScoreLower=6 PrimitiveClass=CLASS_B RealUAF=YES HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO RequiresHostUID0=NO AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 6. * Conservative score: 6; no floor or cap applied. * Raw paranoid score: 7. * Paranoid score: 7; no floor or cap applied. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown * +2 Real UAF: a stale `chann->conn` remains after `struct ksmbd_conn` is freed. * +2 Remote network reachability: an authenticated SMB client can drive binding, subsequent non-binding `SESSION_SETUP`, disconnect, and later session teardown. * +1 Attacker-influenced lifetime sequence: the client materially controls the protocol transitions that create and later consume the stale channel. * +1 Reliable crash/strong DoS: `ksmbd_conn_set_exiting()` writes through the freed pointer; heap corruption plausibly faults or destabilizes the kernel. * Paranoid +1 weak exploit leverage: the vulnerable operation is an actual fixed-field write into freed slab storage, potentially after reuse. Payload, replacement object, and reclaim are not controlled, so this is not Class A. * No extra availability point for the same crash. No C/I, arbitrary write, controlled reclaim, disclosure, or LPE is shown. 3. Reachability analysis The supplied call-path evidence supports a remote authenticated SMB actor rather than host administration or host UID 0. Valid session and multichannel state are prerequisites, but no Linux capability or namespace privilege is indicated. The sequence is protocol-state dependent, not shown to require a narrow timing race or prior privileged host configuration. 4. Primitive and severity reading This is an active structured-object UAF with a concrete post-lifetime write: a stale channel retains a freed connection pointer, and later teardown writes connection state through it. It is broader than a shallow cleanup read because freed heap contents are modified, but the write offset/value appear fixed and no controlled reclaim or useful adjacent victim is demonstrated. Thus it is CLASS_B, not CLASS_A. Remote influence plus the explicit freed-object write leaves material exploit leverage unresolved, requiring Important-class review and prohibiting automatic downgrade. This is not an authorization bypass; B4-PENDING does not apply. 5. One-sentence report phrase An authenticated remote SMB client can preserve a stale multichannel connection pointer and trigger a later kernel heap use-after-free write during session teardown. 6. Manual review advice MANUAL CHECK REQUIRED Review slab reuse, the exact field written by `ksmbd_conn_set_exiting()`, and whether repeated SMB sequences provide placement or replacement-object control. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ksmbd: remove stale channels from all sessions on teardown [ Upstream Commit: f8200bb4994e65a2e5c5b314789eeae39078619d Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f8200bb4994e65a2e5c5b314789eeae39078619d Changed files: fs/smb/server/mgmt/user_session.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=f8200bb4994e65a2e5c5b314789eeae39078619d ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98870 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98870 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:L/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS vector: AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 8.8 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: 6 Paranoid ActionableScore: 7 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: IMPORTANT KPANIC detected for this report: NO Published priority for this report (same as in Subject): IMPORTANT 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).