From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-89693][MODERATE 7.0] nfsd: check nfsd4_acl_to_attr() return value in nfsd4_create() Date: Sat, 12 Sep 2026 02:17:15 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-89693 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: 430ed49a16cf9ca249d0fb51490582090bc4848b List-Id: CVE: CVE-2026-89693 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: nfsd: check nfsd4_acl_to_attr() return value in nfsd4_create() Commit: 430ed49a16cf9ca249d0fb51490582090bc4848b Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=430ed49a16cf9ca249d0fb51490582090bc4848b Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89693 Analysis date: Sat, 12 Sep 2026 02:17:15 -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-2026-89693 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89693 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-2026-89693 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89693 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N';CWE-252;CWE-284;CWE-863;Other CVSS 'AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N';BEST CVSS score: '8.1';DESCR 'NFSv4 CREATE handling in nfsd4_create() can silently ignore an ACL translation error from nfsd4_acl_to_attr() because the saved status is overwritten by later object type handling. A remote NFS client that is allowed to create objects in an export can request an ACL that fails translation and still get the object created without the requested ACL. This can weaken the intended access control policy for files or special objects on a shared NFS export and may allow unintended read or write access depending on mode bits, default ACLs, export policy, and local users. For the CVSS the PR:L is used because the client normally needs valid NFS access and create permission on the target export. The issue is network reachable through the NFS server control path for CREATE operations. Impact is primarily confidentiality and integrity loss from ACL policy bypass, not kernel memory corruption or DoS.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6) YES DANGER DISK NETWORK LINUS KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=6 ActionableScoreLower=5 PrimitiveClass=CLASS_A RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO 1. ActionableScore * Raw conservative score: 5 * Conservative score: 5 * Raw paranoid score: 6 * Paranoid score: 6 * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: No floor or cap changed the score. 2. Signal breakdown Conservative signals: * +2. Concrete access-control policy failure. nfsd4_create() can ignore nfsd4_acl_to_attr() failure and continue CREATE without the requested ACL. * +2. Network reachable service path. The operation is reachable through NFSv4 CREATE requests to an NFS server export. * +1. Confidentiality or integrity policy impact is plausible. Missing ACL application can weaken intended file/object access policy depending on mode bits, default ACLs, export policy, and identities. * -0. No host-admin penalty. The attacker model is a remote NFS client with valid create permission, not host administrator. * -0. No race/timing penalty. This is deterministic return-value mishandling. * -0. No rarity penalty. NFSv4 server ACL handling is a normal deployed service path when NFS exports are used. Paranoid additional signal: * +1. Higher practical security-boundary concern. In deployments where applications rely on atomic CREATE with ACL, silently creating the object without the ACL can create a stronger access-control bypass than a simple malformed request failure. Important non-awarded signals: * RealUAF not awarded. No use-after-free, stale reference, or lifetime corruption is established. * Memory corruption not awarded. No OOB, UAF, double free, arbitrary write, or type confusion is shown. * Reliable kernel crash not awarded. The demonstrated consequence is policy failure, not DoS. * Privileged FD/resource theft not awarded. No downstream protected FD or credential theft chain is supplied. * Practical LPE not awarded. No root escalation or privileged command execution is established. * Extra availability not awarded. There is no availability impact beyond normal request handling. * Namespace-scoped privilege not awarded. The issue is an NFS server network path, not a namespace capability path. 3. Reachability analysis The likely trigger is a remote NFSv4 client that can access an exported filesystem and has permission to create objects in the target directory. The attacker does not need host-admin-equivalent privileges on the NFS server, but does need valid NFS access and CREATE permission in the export. This is therefore below host admin, but not anonymous in the usual case. The issue is network reachable through the NFS server control path for CREATE operations. It is not triggered by passive packet forwarding or unrelated network traffic. Prior administrative setup of an NFS export is required for exposure, but that is the normal deployment condition for nfsd and not a special exploit prerequisite once the service is exposed. No namespace-scoped capability is relevant. No special hardware, sysctl, boot option, race, or timing condition is required. 4. Primitive and severity interpretation The exact primitive is ignored error propagation for an ACL translation failure. nfsd4_acl_to_attr() can fail, but its status is overwritten by later create-type handling, allowing CREATE to continue without the requested ACL. This is not an active structured UAF, fixed stale storage, cleanup-only stale dereference, or repeated release/refcount mutation. It is a security policy semantic failure in filesystem server code. The demonstrated consequence is creation of an object whose ACL does not match the client-requested ACL semantics. The practical security consequence depends on the export configuration, default ACL behavior, umask, identity mapping, and whether applications assume CREATE plus ACL is atomic. PrimitiveClass is CLASS_A because the bug directly affects access-control semantics and can change externally visible object permissions on a network filesystem service. ImportantCandidate is YES because the impact can be more than a harmless request error and may weaken confidentiality or integrity on shared exports. AutoDowngradeAllowed is NO because a meaningful network-reachable access-control policy bypass would be lost by automatic closure. Likely operational severity is Actionable Moderate, with Strong Important review warranted for sensitive NFS exports or environments relying on ACLs for multi-user isolation. 5. One-sentence report phrase A remote NFSv4 client with create permission can cause nfsd4_create() to proceed after ACL translation failure, creating an object without the requested ACL and potentially weakening confidentiality and integrity policy on the export. 6. Manual review recommendation MANUAL CHECK REQUIRED The issue is network reachable and affects NFSv4 ACL enforcement semantics, so real impact depends on export policy, identity mapping, default ACLs, and whether sensitive shared data relies on CREATE with ACL behavior. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: nfsd: check nfsd4_acl_to_attr() return value in nfsd4_create() Commit: 430ed49a16cf9ca249d0fb51490582090bc4848b Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=430ed49a16cf9ca249d0fb51490582090bc4848b Commit description: nfsd4_create() stores the return value of nfsd4_acl_to_attr() in status, but the switch(create->cr_type) block unconditionally overwrites it in every branch. ACL translation errors are silently discarded, and the CREATE proceeds without the requested ACL. Add an early exit check after nfsd4_acl_to_attr(), matching the pattern already used in nfsd4_setattr(). Fixes: c0cbe70 ("NFSD: add posix ACLs to struct nfsd_attrs") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Jeff Layton [ cel: prefer NFS4ERR_BADTYPE over NFS4ERR_ATTRNOTSUPP ] Link: https://patch.msgid.link/20260611-nfsd-testing-v2-5-5b90e276f2d9@kernel.org Signed-off-by: Chuck Lever [ retained unconditional ACL conversion because the older helper already handles null ACLs ] Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman Changed files: fs/nfsd/nfs4proc.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=430ed49a16cf9ca249d0fb51490582090bc4848b ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89693 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89693 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:L/UI:N/S:U/C:L/I:L/A:N The Best / paranoid CVSS vector: AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N The Best / paranoid CVSS score: 8.1 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).