From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-89691][MODERATE 7.0] nfsd: clear opcnt on compound arg release to prevent OOB read Date: Fri, 11 Sep 2026 22:46:45 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-89691 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: 6 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: 58bcdfb2b2e412088839ae740b1a95154dc0b8d0 List-Id: CVE: CVE-2026-89691 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: nfsd: clear opcnt on compound arg release to prevent OOB read Commit: 58bcdfb2b2e412088839ae740b1a95154dc0b8d0 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=58bcdfb2b2e412088839ae740b1a95154dc0b8d0 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89691 Analysis date: Fri, 11 Sep 2026 22:46:45 -0400 ActionableScore: 6 ActionableScore lower bound: 5 Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89691 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89691 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-2026-89691 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89691 CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N';CWE-125;*CWE-200;CWE-665;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '4.7';DESCR 'An out-of-bounds read in the NFSD rpc_status reporting path can expose adjacent slab memory because nfsd4_release_compoundargs resets args ops to the inline iops array but leaves args opcnt stale. A remote NFS client can influence compound metadata and error paths, while a local user that can query the RPC status netlink interface may receive leaked kernel memory when the status counter remains in the in progress state. For the CVSS the PR:L is used for the paranoid score because practical data retrieval requires a local process or service account with access to the netlink status interface, even though stale metadata can be influenced by NFS traffic. The issue is network adjacent for the trigger and local for the leak sink. Impact is primarily confidentiality loss from kernel memory disclosure, with no direct write primitive or kernel crash shown by the patch context. NFS servers are typically deployed inside trusted internal or data-center networks rather than exposed to the public Internet.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6) YES OOB DISK SIMPLEFIX LEAK ERRORPATH NETWORK LINUS KPANIC KPANIC LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=6 ActionableScoreLower=5 PrimitiveClass=CLASS_A RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO 1. ActionableScore * Raw conservative score: 5 * Conservative score: 5. No floor or cap applied. * Raw paranoid score: 6 * Paranoid score: 6. No floor or cap applied. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown Conservative positive signals: * +2: Concrete user-visible kernel information disclosure. The bug is an OOB read from args->ops after it has been reset to inline iops[8] while opcnt remains stale, and the supplied context states that adjacent slab memory is leaked to userspace through the RPC status netlink dump path. * +1: Below-host-admin local retrieval path. The supplied analysis states that a local user or service account able to query the RPC status netlink interface can receive the leaked data, so host administrator privilege is not positively required for the leak sink. * +1: Confidentiality impact is plausible and concrete. This is not merely an internal invalid read, because the out-of-bounds bytes are exposed to userspace. * +1: Practical trigger-to-disclosure chain is established at a high level. Remote NFS compound metadata and error paths can influence the stale opcnt state, and the local status dump path can disclose the stale out-of-bounds data. Paranoid additional signal: * +1: Higher disclosure sensitivity. Adjacent slab memory disclosure from kernel objects may expose sensitive kernel data or pointers, so a higher manual-review score is defensible even though arbitrary read, write, or privilege escalation is not shown. Non-awarded or withheld signals: * RealUAF not awarded. The issue is stale metadata and OOB read, not a post-free object dereference. * Controlled reclaim not demonstrated. * Arbitrary write not demonstrated. * Integrity impact not awarded. The patch and supplied context show read disclosure, not unauthorized modification. * Reliable kernel crash not awarded. The described consequence is information leak via netlink, not panic or host-wide DoS. * Remote reachable +2 not awarded. A remote NFS client may influence the stale compound state, but the demonstrated disclosure sink is local netlink status retrieval, so the complete leak path is not purely remote. * Race penalty not applied. The rq_status_counter odd state is an error-path state condition, not evidence of a narrow externally uncontrollable timing race. * No privilege penalty applied. Host-admin-equivalent privilege is not positively established for the complete disclosure path. 3. Reachability analysis The trigger has two relevant stages. A remote NFS client can influence NFSv4 compound metadata and may help create the stale opcnt condition through an error path after rq_status_counter is set odd. The actual disclosure is through the RPC status netlink dumpit handler, which is a local userspace-facing sink. Based on the supplied hint, the evaluated attacker for the actionable score is a below-host-admin local user or service account that can query the RPC status netlink interface. Therefore HostAdminRequired=NO. If a target distribution restricts this netlink interface to host administrators, the practical score could be lower, but that restriction is not established by the supplied input. NamespaceScopedPrivilege is UNKNOWN. The supplied material does not establish that the complete trigger and disclosure path is reachable through attacker-created namespaces. Prior NFS server setup is required in the sense that nfsd and rpc_status support must be present and active, but this is not scored as a rare configuration penalty because the supplied issue is specifically in an NFS server status interface and no unusual hardware or boot-only feature is required. 4. Primitive and severity interpretation The exact primitive is a bounded out-of-bounds read from the inline iops[8] array after args->ops is reset while args->opcnt remains stale. Because iops is the last field in struct nfsd4_compoundargs, indices 8 through 15 can read adjacent slab memory. The supplied context states that this data is leaked to userspace via netlink, making this a concrete information disclosure primitive rather than a harmless internal OOB read. This is not an active structured UAF and not fixed stale storage after free. It is stale compound metadata causing a later read beyond the intended inline array. There is no concrete repeated release or refcount mutation. PrimitiveClass=CLASS_A is used because a kernel memory disclosure to userspace is directly established. It is a low-end Class A case rather than a high-end Important case because the read appears bounded, local retrieval is required, and no arbitrary read, write, LPE, or crash primitive is shown. ImportantCandidate=YES because kernel slab disclosure can expose sensitive data and should not be automatically downgraded without confirming access restrictions and leaked object content. AutoDowngradeAllowed=NO because the issue has a concrete confidentiality primitive, not merely a warning, crash, or bookkeeping defect. Likely operational severity is actionable Moderate, with Strong Important review warranted if the netlink status interface is broadly accessible or the leaked adjacent slab contents include kernel pointers, credentials, secrets, or other sensitive state. 5. One-sentence report phrase An OOB read in the NFSD rpc_status path can leak adjacent slab memory to a local netlink reader when stale NFSv4 compound opcnt metadata survives argument release. 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the patch and supplied context establish an actual kernel memory disclosure path to userspace, and the practical severity depends on rpc_status netlink access controls and the sensitivity of adjacent slab contents. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: nfsd: clear opcnt on compound arg release to prevent OOB read Commit: 58bcdfb2b2e412088839ae740b1a95154dc0b8d0 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=58bcdfb2b2e412088839ae740b1a95154dc0b8d0 Commit description: nfsd4_release_compoundargs() resets args->ops to the inline iops[8] array when the dynamically-allocated ops buffer is freed, but leaves args->opcnt at its original value (which can be up to 200 for NFSv4.1+ compounds). If rq_status_counter is stuck at an odd value (which can happen when nfsd_dispatch() hits an error path after setting it odd), the RPC status dumpit handler reads min(opcnt, 16) entries from args->ops[]. Since iops only has 8 elements and is the last field in struct nfsd4_compoundargs, reading indices 8-15 accesses adjacent slab memory and leaks it to userspace via netlink. Zero opcnt unconditionally in nfsd4_release_compoundargs() so stale compound metadata is never exposed through the status interface. Fixes: bd9d6a3 ("NFSD: add rpc_status netlink support") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Jeff Layton [ cel: Remove the kvfree_rcu_mightsleep() sleep from the exposure window ] Link: https://patch.msgid.link/20260611-nfsd-testing-v2-1-5b90e276f2d9@kernel.org Signed-off-by: Chuck Lever Signed-off-by: Greg Kroah-Hartman Changed files: fs/nfsd/nfs4xdr.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=58bcdfb2b2e412088839ae740b1a95154dc0b8d0 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89691 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89691 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:L/UI:N/S:U/C:L/I:N/A:N The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N 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: 5 Paranoid ActionableScore: 6 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).