From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98681][MODERATE 7.0] smb: client: split cifsFileInfo bitfields to avoid shared-byte RMW races Date: Sat, 24 Oct 2026 06:09:52 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98681 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: 1 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 3786ee67658a2c80fef2544e7de2cd329e043cf9 List-Id: CVE: CVE-2026-98681 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: smb: client: split cifsFileInfo bitfields to avoid shared-byte RMW races Commit: 3786ee67658a2c80fef2544e7de2cd329e043cf9 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3786ee67658a2c80fef2544e7de2cd329e043cf9 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98681 Analysis date: Sat, 24 Oct 2026 06:09:52 -0400 ActionableScore: 1 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: Concurrent updates to packed CIFS file-state flags can lose one another and disrupt SMB operations, without a demonstrated memory-corruption or authorization primitive. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98681 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98681 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: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-98681 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98681 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=MODERATE_KPANIC RESULT=SAME V39_AEGIS_ONE_STEP_UP=MODERATE->MODERATE_KPANIC (final reconciliation agrees; DECISION: both MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-362;CWE-667;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'The SMB client stored invalidHandle, swapfile, oplock_break_cancelled, status_file_deleted, and offload in one bitfield byte even though different paths update them under different locks. Concurrent byte level read modify write operations can lose an update to another flag and leave cifsFileInfo in a stale logical state. The race can affect handle recovery, deleted file close behavior, oplock cancellation, workqueue offload, or SMB swap handling. No UAF, OOB access, information leak, or arbitrary write primitive is established. Attack complexity is high because a specific concurrency window must be reached. For the CVSS the PR:N value reflects a malicious or compromised SMB server that needs no privileges on the client after an SMB mount is connected, although reliable triggering also depends on concurrent client activity. Availability impact is normally limited to SMB file or mount disruption. The paranoid vector allows high availability impact if the stale state blocks critical storage or network swap, but it does not assign confidentiality or integrity impact. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 5.3 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. final reconciliation stage MODERATE to MODERATE_KPANIC because the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 0 with primitive class NONE and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) MAYBE DISK SIMPLEFIX RACE SERVERTOCLIENT LINUS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 KPANIC V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=1 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 1. * Conservative score: 1; no floor or cap applied. * Raw paranoid score: 1. * Paranoid score: 1; critical-storage or swap disruption does not establish a separate host-wide impact. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 weak/indirect state corruption: concurrent byte-wide read-modify-write operations can lose updates to active `cifsFileInfo` flags. * +1 availability impact plausible: stale flags can disrupt SMB handle recovery, close processing, oplock cancellation, offload, or swap behavior. * -1 hard concurrency requirement: triggering requires overlapping updates from differently locked paths; the supplied evidence explicitly describes a specific race window. * No UAF, OOB write, arbitrary write, disclosure, authorization bypass, or protected-state integrity effect is shown. * No remote-reachability bonus: an existing SMB mount and concurrent client activity are prerequisites, and direct server control over the complete interleaving is not established. * NEW52/B5-R does not apply: there is no retry-accumulated heap OOB write or later consumption of OOB-corrupted state. * NEW53/B3-PENDING does not apply: no shared-backing write is present. 3. Reachability analysis A malicious or compromised SMB server may influence activity after a client mount exists, but the patch does not establish that it controls every updater or can reliably force the race. Mount setup and the credentials needed to create it are unspecified, so host-admin and namespace-scoped reachability remain unknown. No special hardware is required. 4. Primitive and severity reading The primitive is a shared-byte RMW race causing lost flag updates in an active structured file object. This is logical-state corruption, not kernel-memory corruption: all writes remain within the intended byte, and no stale lifetime or pointer use is shown. The demonstrated consequence is SMB operation or mount disruption; host panic, persistent storage corruption, or attacker-useful integrity leverage is unproven. It is therefore CLASS_C, not an Important candidate, and ordinary Moderate downgrade is allowed. 5. One-sentence report phrase Concurrent updates to packed CIFS file-state flags can lose one another and disrupt SMB operations, without a demonstrated memory-corruption or authorization primitive. 6. Manual review advice MANUAL CHECK RECOMMENDED Confirm whether server-controlled requests can reliably coordinate the conflicting update paths or affect critical network swap. 7. Call-site confidence Call-site confidence: low ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: smb: client: split cifsFileInfo bitfields to avoid shared-byte RMW races Commit: 3786ee67658a2c80fef2544e7de2cd329e043cf9 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3786ee67658a2c80fef2544e7de2cd329e043cf9 Commit description: The invalidHandle, swapfile, oplock_break_cancelled, offload, and status_file_deleted fields are stored in the same bitfield byte in struct cifsFileInfo, but are updated in different code paths that may run simultaneously, and are protected by different locks. Since bitfield assignments generate byte-level read-modify-write operations, a modification to one flag can overwrite a concurrent modification to another flag. To avoid these races, convert these flags from a bitfield to separate bool fields. Closes: https://lore.kernel.org/r/7689764e-c0f6-4016-9557-b54cf4a3de4e@redhat.com Fixes: 3bc303c ("cifs: convert oplock breaks to use slow_work facility (try #4)") Fixes: 4e8aea3 ("smb3: enable swap on SMB3 mounts") Fixes: ffceb76 ("smb: client: do not defer close open handles to deleted files") Fixes: 173217b ("smb3: retrying on failed server close") Signed-off-by: Frank Sorenson Cc: stable@vger.kernel.org Reviewed-by: Namjae Jeon Signed-off-by: Paulo Alcantara Signed-off-by: Greg Kroah-Hartman Changed files: fs/smb/client/cifsglob.h 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=3786ee67658a2c80fef2544e7de2cd329e043cf9 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98681 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98681 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:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.3 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: 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: 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).