From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-89688][MODERATE 7.0] nfsd: drop the stateid, not the stateowner, on seqid_op replay retry Date: Fri, 11 Sep 2026 23:30:05 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-89688 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: 7 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: 69ed78b6b947c9257213164678b4edf17533093b List-Id: CVE: CVE-2026-89688 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: nfsd: drop the stateid, not the stateowner, on seqid_op replay retry Commit: 69ed78b6b947c9257213164678b4edf17533093b Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=69ed78b6b947c9257213164678b4edf17533093b Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89688 Analysis date: Fri, 11 Sep 2026 23:30:05 -0400 ActionableScore: 7 ActionableScore lower bound: 5 Actionable bucket: Strong Important candidate Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89688 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89688 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-2026-89688 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89688 CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-911;CWE-362;Other CVSS 'AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'An NFS server state handling bug can occur in nfs4_preprocess_seqid_op because the retry path drops a stateowner reference that was not acquired while leaking the stid reference that was actually held. This can cause stateowner refcount underflow and a possible use-after-free, and the leaked stid reference can also stall close processing that waits for sc_count to drop. For the CVSS the PR:L is used because a remote attacker typically needs NFS access sufficient to create or replay NFSv4 stateful operations, but does not need local code execution on the server. The issue is network reachable when the NFS server is exposed to the attacker, although NFS services are usually limited to trusted storage or internal networks. Impact is at least denial of service via kernel crash or stuck state cleanup, and in the paranoid case may include confidentiality and integrity impact due to the UAF class.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 6) YES OOB DEADLOCK DISK LEAK ERRORPATH UAF NETWORK LINUS KPANIC DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=7 ActionableScoreLower=5 PrimitiveClass=CLASS_B RealUAF=YES HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO 1. ActionableScore * Raw conservative score: 5 * Conservative score: 5. FLOOR 5 applies but does not change the score. * Raw paranoid score: 7 * Paranoid score: 7. No floor or cap changes the score. * Final recommended bucket: **Strong Important candidate**:: 2. Signal breakdown Conservative signals: * +2 Real UAF / lifetime violation. The retry path calls nfs4_put_stateowner() on a stateowner reference that was not acquired, which can underflow so_count and cause use-after-free. * +2 Network reachable. The affected code is in NFS server NFSv4 state operation handling and can be reached by a remote NFS client with sufficient protocol access. * +1 Reliable kernel crash / strong DoS. The described refcount underflow and UAF can crash the kernel, and the leaked stid reference can stall close cleanup. * +1 Concrete persistent resource/reference leak. The sc_count reference acquired on the stid is leaked on the buggy retry path. * -1 Hard timing / teardown condition. The vulnerable path requires the replay owner to be in teardown with RP_UNHASHED and nfsd4_cstate_assign_replay() returning -EAGAIN. Paranoid additional signals: * +1 Attacker-influenced active-object lifetime concern. A remote NFSv4 client can influence creation, replay, and teardown of stateful server objects, and the vulnerable operation mutates lifetime state of an active structured object. * The conservative -1 timing penalty is not applied in the paranoid score because repeated NFS state operations may make the teardown window practically reachable under load. Important non-awarded signals: * Controlled reclaim is not demonstrated. * Arbitrary kernel read or write is not demonstrated. * Callback or function-pointer control is not demonstrated. * Confidentiality and integrity bonuses are not awarded directly. The score preserves the unresolved UAF and refcount-corruption risk instead. * Extra availability is not awarded because the crash and cleanup stall are already covered by the DoS and reference leak signals. * Concrete repeated release/refcount on the exact same dangling reference is not fully established as a two-step same-reference double-put sequence. The bug is still a concrete wrong lifetime/refcount mutation. * Weak LPE is not separately awarded because that would double count the same unresolved lifetime corruption concern. * Strong LPE / Class A is not awarded because no controlled reclaim, arbitrary R/W, or demonstrated privilege escalation is supplied. Repeated-release/refcount checklist: * First release can end lifetime: yes, nfs4_put_stateowner() can decrement so_count and may destroy/free the stateowner. * Exact same reference survives into a second concrete put: not established from the supplied patch. * Second operation is a real lifetime/refcount mutation: not established as a separate second put on the same dangling reference. * +1 Concrete repeated release/refcount: not awarded. * Paranoid repeated-refcount leverage +1: not awarded under the strict repeated-release rule. * FLOOR 5: applied because RealUAF=YES, host-admin privilege is not required, the object is active structured NFS server state, and the bug is a network-reachable lifetime/refcount corruption rather than fixed stale storage. 3. Reachability analysis A remote NFSv4 client with access to the server can plausibly reach nfs4_preprocess_seqid_op() through stateful operations involving stateids and replay handling. This does not require local code execution or host administrator privileges on the NFS server, so HostAdminRequired=NO. The attacker still likely needs NFS protocol access to the exported service and suitable NFSv4 state, so this is not anonymous Internet reachability in every deployment. NFS servers are commonly restricted to storage or internal networks, but that is a deployment restriction rather than a code-level host-admin requirement. NamespaceScopedPrivilege=NO because this is not a namespace-local capability path. The relevant exposure is the host NFS server network service. There is a timing/state condition: the replay owner must be in teardown and nfsd4_cstate_assign_replay() must return -EAGAIN. This supports AC:H-like reasoning for CVSS and the conservative -1 ActionableScore timing penalty, but it does not make the issue local-only or host-admin-only. No special hardware is required. Prior setup is the normal existence and exposure of an NFS server. 4. Primitive and severity interpretation The exact primitive is a wrong reference ownership operation in NFS server state handling. nfsd4_lookup_stateid() returns a stateid/stid reference, but the error path drops the associated stateowner instead of dropping the stid reference actually held. This is an active structured object lifetime bug, not fixed stale storage. The affected stateowner and stid participate in NFSv4 state management, replay handling, close processing, and refcount-based lifetime control. The demonstrated consequences are stateowner refcount underflow, possible use-after-free, leaked stid reference, kernel crash, and stalled close cleanup. The speculative consequence is stronger exploitation through post-lifetime corruption of active NFS server state, but no controlled reclaim or arbitrary write is shown. PrimitiveClass=CLASS_B because a real kernel lifetime/refcount corruption primitive is established, but Class A exploitation leverage is not demonstrated. ImportantCandidate=YES because this is a network-reachable active-object UAF/refcount corruption in kernel nfsd state, and the exploitation leverage beyond crash is materially unresolved. AutoDowngradeAllowed=NO because automatically closing this as ordinary DoS would discard a concrete network-reachable kernel lifetime/refcount corruption primitive. Likely operational severity is at least actionable Moderate. The paranoid interpretation reaches Strong Important candidate because of remote NFS reachability and unresolved active-object UAF/refcount corruption. 5. One-sentence report phrase A network-reachable NFSv4 server state handling bug drops an unowned stateowner reference on a replay retry path, causing possible refcount underflow, use-after-free, leaked stid references, kernel crash, or stalled state cleanup. 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the patch establishes a real network-reachable kernel lifetime/refcount corruption primitive with possible UAF in active NFS server state, and exploitation leverage beyond DoS is unresolved. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: nfsd: drop the stateid, not the stateowner, on seqid_op replay retry Commit: 69ed78b6b947c9257213164678b4edf17533093b Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=69ed78b6b947c9257213164678b4edf17533093b Commit description: In nfs4_preprocess_seqid_op() the stateid is obtained from nfsd4_lookup_stateid(), which holds a reference on the nfs4_stid (sc_count) but takes no reference on the stateowner. openlockstateid() merely casts that stid and likewise takes no reference. When nfsd4_cstate_assign_replay() returns -EAGAIN (the replay owner is being torn down, RP_UNHASHED) it has not taken a stateowner reference on that path. The error handling nevertheless called nfs4_put_stateowner(stp->st_stateowner), dropping an so_count reference the function never acquired -- risking a stateowner refcount underflow and use-after-free -- while leaking the sc_count reference held on the stid. The leaked stid reference can also stall a concurrent nfsd4_close_open_stateid() waiting for sc_count to drop. Drop the reference actually held -- the stid -- before retrying. The stateowner stays alive through the reference held by the stid. This mirrors the open path in nfsd4_process_open1(), where the put balances a reference that path explicitly holds on the stateowner. Fixes: eec7620 ("nfsd: replace rp_mutex to avoid deadlock in move_to_close_lru()") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Jeff Layton Link: https://patch.msgid.link/20260611-nfsd-testing-v2-21-5b90e276f2d9@kernel.org Signed-off-by: Chuck Lever Signed-off-by: Greg Kroah-Hartman Changed files: fs/nfsd/nfs4state.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=69ed78b6b947c9257213164678b4edf17533093b ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89688 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89688 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:L/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS vector: AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/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: 5 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: 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).