From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-89664][MODERATE 7.0] nfsd: release OPEN-decoded posix ACLs via op_release Date: Sat, 12 Sep 2026 04:07:56 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-89664 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: 4 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: 5b3a7d7c23c071efe12dd1bc1d2e5f97c4892921 List-Id: CVE: CVE-2026-89664 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: nfsd: release OPEN-decoded posix ACLs via op_release Commit: 5b3a7d7c23c071efe12dd1bc1d2e5f97c4892921 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5b3a7d7c23c071efe12dd1bc1d2e5f97c4892921 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89664 Analysis date: Sat, 12 Sep 2026 04:07:56 -0400 ActionableScore: 4 ActionableScore lower bound: 3 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-2026-89664 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89664 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-2026-89664 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89664 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';*CWE-401;*CWE-772;**CWE-400;Other CVSS 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '7.5';DESCR 'NFSD can leak refcounted POSIX ACL objects decoded from NFSv4 OPEN create attributes when a malformed OPEN compound exits through a non seqid mutating error path before nfsd4_open runs, or when a replay encoding path bypasses operation release handling. A remote NFS client that can reach the NFSv4 server and send crafted OPEN compounds with valid POSIX ACL attributes can repeat the condition and gradually consume kernel memory. For the CVSS the PR:N is used because exploitation does not require local code execution or privileges on the target host beyond network reachability to the NFS service. The issue is network reachable over NFS but practical exposure is usually limited to hosts that expose nfsd to trusted internal networks. Impact is denial of service via memory exhaustion, with no evidence of UAF, arbitrary write, information disclosure, or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) SKIP CVE-2026-89664 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE DISK LEAK NETWORK KPANIC KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=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: 4 * Paranoid score: 4. No floor or cap applied. * Final recommended bucket: **Borderline / manual review recommended**:: 2. Signal breakdown Conservative signals: * +2 Remote reachable / directly network-triggerable. A remote NFSv4 client that can reach nfsd can send malformed OP_OPEN compounds carrying valid POSIX ACL create attributes. * +1 Concrete persistent kernel resource/reference leak. The patch establishes that refcounted `struct posix_acl` references allocated during OPEN decode can be lost on the short-circuit and replay paths. * 0 Reliable kernel crash not awarded. The demonstrated defect is a leak, not an immediate Oops or panic. * 0 Confidentiality and integrity not awarded. No UAF, arbitrary write, information disclosure, protected object modification, or authorization bypass is established. * 0 RealUAF not awarded. The issue is missing release of references, not stale post-free use. * 0 Concrete repeated release/refcount signal not awarded. The bug is the absence of `posix_acl_release()`, not a second release through a dangling reference. Paranoid additional signal: * +1 Sustained resource exhaustion concern. Because each malformed eligible compound can leak kernel ACL references, repeated remote requests can plausibly accumulate memory pressure and produce DoS. Negative signals: * No host-admin penalty. Host-admin-equivalent privilege is not required to send NFSv4 requests to an exposed nfsd service. * No rare-subsystem penalty. NFS server exposure is deployment-dependent, but not rare enough by itself to subtract points. * No race/timing penalty. The trigger is an ordered error/replay path, not a narrow timing race. 3. Reachability analysis The evaluated attacker is a remote NFS client with network reachability to the NFSv4 server. No local code execution on the target host is required. No host-admin-equivalent privilege is established as necessary for the trigger. Practical exposure depends on nfsd being enabled and reachable, and on the server accepting enough NFSv4 protocol interaction for the malformed OPEN compound to reach the affected decode and dispatch paths. NFS servers are often limited to trusted internal networks or storage networks, but that is an environmental restriction rather than a code-level privilege requirement. No namespace-scoped privilege issue is involved. No special hardware, boot mode, or race timing is required. 4. Primitive and severity interpretation The exact primitive is a concrete persistent reference leak of refcounted POSIX ACL objects attached to an NFSv4 OPEN operation. The affected objects are allocated by `posix_acl_alloc()` through the OPEN attribute decode path and should be released after compound operation processing. This is not an active structured UAF and not fixed stale storage. It is a resource/lifetime cleanup defect where references are lost on specific control-flow paths. The short-circuit path can avoid `nfsd4_open()`, and the replay path previously bypassed operation release handling. There is no concrete repeated release/refcount mutation. The first lifetime operation is allocation/acquisition of ACL references. The vulnerable path omits the matching release. There is no second `put` or `release` through a potentially dangling object. PrimitiveClass is CLASS_C because the demonstrated behavior is remote DoS by resource exhaustion without a useful corruption, ownership, authorization, disclosure, or LPE primitive. ImportantCandidate is NO because the patch supports memory/resource exhaustion only. AutoDowngradeAllowed is YES because no unresolved memory corruption, repeated stale refcount mutation, security-boundary bypass, or ownership violation remains. Likely operational severity is Moderate-like but actionable for exposed NFS servers, especially where untrusted clients can reach nfsd. 5. One-sentence report phrase A remote NFSv4 client can trigger an NFSD OP_OPEN error or replay path that leaks refcounted POSIX ACL objects, allowing sustained kernel memory exhaustion DoS without evidence of UAF, arbitrary write, information disclosure, or privilege escalation. 6. Manual review recommendation MANUAL CHECK RECOMMENDED Reason: the issue is network reachable and repeatable against exposed nfsd services, but the established primitive is a resource/reference leak only and does not currently support Important-class memory corruption or privilege escalation. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: nfsd: release OPEN-decoded posix ACLs via op_release Commit: 5b3a7d7c23c071efe12dd1bc1d2e5f97c4892921 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5b3a7d7c23c071efe12dd1bc1d2e5f97c4892921 Commit description: nfsd4_decode_createhow4() calls nfsd4_decode_fattr4(), which allocates refcounted struct posix_acl objects via posix_acl_alloc() and stores them in open->op_pacl and open->op_dpacl. These pointers must be released once the OPEN compound finishes. When nfsd4_decode_open_claim4() returns a non-seqid-mutating error, the dispatcher short-circuits before op_func runs: nfsd4_proc_compound() if (op->status && op->opnum == OP_OPEN) op->status = nfsd4_open_omfg(...) if (!seqid_mutating_err(ntohl(op->status))) return op->status; /* nfsd4_open() never runs */ ... opdesc->op_release(&op->u) /* must still release op_pacl/op_dpacl */ Before this change OP_OPEN had no .op_release in nfsd4_ops[], and the release pair lived inside nfsd4_open() at its out_err: label. On the short-circuit path nfsd4_open() is never invoked, so both posix_acl refs leak on every malformed OPEN compound that carries valid POSIX ACL createhow4 attributes. Add nfsd4_open_release() and wire it as .op_release for OP_OPEN. posix_acl_release() is NULL-safe, so the single release site covers both the normal path and the nfsd4_open_omfg short-circuit. Remove the matching posix_acl_release() pair from nfsd4_open()'s out_err: label to avoid double-releasing. The compound loop has two encoding branches: nfsd4_encode_operation() for normal ops, and nfsd4_encode_replay() for v4.0 replayed ops. op_release was only called from nfsd4_encode_operation(), so resources attached to op->u leak on the replay path. Move the op_release() call out of nfsd4_encode_operation() and the replay branch, placing it after the if-else in nfsd4_proc_compound(). This gives a single call site in a fairly obviously-correct place, covering both the normal encoding and replay paths. Fixes: 5fc51df ("NFSD: Add support for XDR decoding POSIX draft ACLs") Cc: stable@vger.kernel.org Signed-off-by: Chris Mason Reviewed-by: NeilBrown Signed-off-by: Jeff Layton Link: https://patch.msgid.link/20260601-nfsd-testing-v3-1-a31cd10bdd4f@kernel.org Signed-off-by: Chuck Lever Signed-off-by: Greg Kroah-Hartman Changed files: fs/nfsd/nfs4proc.c 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=5b3a7d7c23c071efe12dd1bc1d2e5f97c4892921 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89664 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89664 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:N/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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: 3 Paranoid ActionableScore: 4 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).