From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-90149][MODERATE REGULAR] NFSv4/flexfiles: fix NULL dereference for NFSv4.0 data servers [ Upstream Date: Thu, 17 Sep 2026 21:28:15 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-90149 X-AL-KERNEL-Priority: MODERATE REGULAR X-AL-KERNEL-Severity: MODERATE REGULAR X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 3 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 163c16e01f53fc8eb8d0f3484ae6c382265ecbbd List-Id: CVE: CVE-2026-90149 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: NFSv4/flexfiles: fix NULL dereference for NFSv4.0 data servers [ Upstream Commit: 163c16e01f53fc8eb8d0f3484ae6c382265ecbbd Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=163c16e01f53fc8eb8d0f3484ae6c382265ecbbd Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90149 Analysis date: Thu, 17 Sep 2026 21:28:15 -0400 ActionableScore: 3 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-2026-90149 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90149 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: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-90149 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-90149 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-754;CWE-703;Other CVSS 'AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:N/A:H';BEST CVSS score: '5.9';DESCR 'A NULL pointer dereference in the NFSv4 flexfiles client path can occur because NFSv4.0 data servers do not have cl_session, while nfs4_init_ds_session and ff_layout_async_handle_error_v4 assumed that a session exists. A malicious or compromised NFS server or data server setup can trigger the bug when a client performs I/O through a flexfiles layout that uses an NFSv4.0 data server, especially on DS I/O error handling. For the CVSS the PR:N is used because the attacker does not need a local account on the victim, but must influence the NFS server or data server endpoint used by the client. The issue is network reachable in NFS deployments, but practical exposure is usually limited to trusted storage or data center networks rather than the public Internet. Impact is denial of service via kernel oops or repeated renewal work. No direct privilege escalation or information disclosure primitive is indicated by the code change.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) YES DANGER NULLPTR DISK INIT SIMPLEFIX NETWORK LINUS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=3 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 3 * Conservative score: 3. No floor or cap applied. * Raw paranoid score: 3 * Paranoid score: 3. No floor or cap applied. * Final recommended bucket: **Borderline / manual review recommended**:: 2. Signal breakdown Positive signals: * +2 Remote or network-influenced reachability. A malicious or compromised NFS server or data server can influence the NFSv4 flexfiles client path when the victim client performs I/O through a flexfiles layout using an NFSv4.0 data server. * +1 Reliable kernel crash / strong DoS. The patch description directly states that I/O to a v4.0 flexfiles DS oopses due to NULL dereferences of clp->cl_session. Negative signals: * No host-admin penalty was applied. The attacker model is a malicious or compromised NFS server endpoint used by the client, not a local host administrator on the victim. * No rare-subsystem penalty was applied. pNFS flexfiles with an NFSv4.0 data server is a specific deployment condition, but the supplied evidence does not justify treating it as rare enough to subtract points under the scoring rules. * No race or timing penalty was applied. The bug is a deterministic NULL session handling error, not a narrow race. Important non-awarded signals: * RealUAF not awarded. The evidence shows NULL pointer dereference, not use-after-free or stale post-lifetime object use. * Controlled reclaim not demonstrated. * Arbitrary or directed kernel write not demonstrated. * Confidentiality and integrity signals not awarded. The code change shows invalid NULL dereference and incorrect lease/session handling, not disclosure or unauthorized modification. * Strong LPE or weak LPE concern not awarded. No exploitation primitive beyond crash or renewal-loop behavior is established. * Extra Availability not awarded. The lease renewal requeue behavior is noted, but the primary established security consequence remains client-side DoS and the same availability issue should not be double-counted. 3. Reachability analysis The relevant attacker is a malicious or compromised NFS server or data server endpoint that the victim NFS client uses. The trigger occurs when the client performs I/O through a pNFS flexfiles layout that accepts an NFSv4.0 data server. The attacker does not need a local account on the victim host in this model, so HostAdminRequired=NO. However, practical exposure depends on the victim already using NFS and pNFS flexfiles with such a data server. This is more likely in trusted storage or data-center networks than on the public Internet. No namespace-scoped privilege is involved, so NamespaceScopedPrivilege=NO. No special race timing is required. No special hardware requirement is shown. 4. Primitive and severity interpretation The exact primitive is a NULL pointer dereference of clp->cl_session in NFSv4 flexfiles client code. NFSv4.0 data server clients do not have a session and use clp->cl_slot_tbl instead. Two paths incorrectly assumed cl_session exists: nfs4_init_ds_session while seeding the DS lease, and ff_layout_async_handle_error_v4 during DS I/O error handling. This is not an active structured UAF and not fixed stale storage. It is a CLASS_C invalid-state / NULL-dereference issue. The demonstrated consequence is client kernel oops or DoS, plus repeated renewal work caused by an unseeded lease time. The speculative consequence would be broader client disruption in affected storage deployments, but no memory corruption, privilege escalation, or information disclosure primitive is supported by the patch. ImportantCandidate=NO because the established primitive is crash/DoS only and does not leave unresolved memory-corruption or authorization-boundary leverage. AutoDowngradeAllowed=YES because this is a Class C NULL dereference with no UAF, no repeated lifetime mutation, no controlled corruption, and no security-boundary bypass. ManualReview=RECOMMENDED because the issue is network-influenced kernel client DoS and depends on deployment-specific NFS server trust boundaries. 5. One-sentence report phrase A malicious or compromised NFS server can cause an NFSv4 flexfiles client using an NFSv4.0 data server to dereference a NULL cl_session during I/O or error handling, leading to client kernel DoS without evidence of memory corruption or privilege escalation. 6. Manual review recommendation MANUAL CHECK RECOMMENDED Reason: the bug is network-influenced and affects kernel NFS client code, but the established primitive is a NULL pointer dereference and DoS only. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: NFSv4/flexfiles: fix NULL dereference for NFSv4.0 data servers [ Upstream Commit: 163c16e01f53fc8eb8d0f3484ae6c382265ecbbd Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=163c16e01f53fc8eb8d0f3484ae6c382265ecbbd Changed files: fs/nfs/flexfilelayout/flexfilelayout.c fs/nfs/nfs4session.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=163c16e01f53fc8eb8d0f3484ae6c382265ecbbd ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-90149 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90149 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:H/PR:N/UI:R/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.9 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: 3 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 alexanjelausa@gmail.com (and both send reply to CVE record itself too and see "reply" button below for howto reply).