From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-97927][LOW] ufs: create the root dentry after loading cylinder metadata Date: Sat, 26 Sep 2026 14:46:33 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-97927 X-AL-KERNEL-Priority: LOW X-AL-KERNEL-Severity: LOW X-AL-KERNEL-Base-Severity: LOW X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 0 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: a9804121d55aaa4319c1cac00b99794aa177dd6a List-Id: CVE: CVE-2026-97927 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: ufs: create the root dentry after loading cylinder metadata Commit: a9804121d55aaa4319c1cac00b99794aa177dd6a Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a9804121d55aaa4319c1cac00b99794aa177dd6a Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97927 Analysis date: Sat, 26 Sep 2026 14:46:33 -0400 ActionableScore: 0 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-97927 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97927 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: LOW Manual review required: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-97927 LOW https://www.kernelcve.org/list/?q=CVE-2026-97927 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-665;CWE-703;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A NULL pointer dereference in ufs_fill_super can occur when a writable UFS mount publishes sb s_root before cylinder group metadata has been loaded successfully. A crafted filesystem image can make ufs_read_cylinder_structures fail after the root dentry is installed, leaving sb s_root present while sb s_fs_info has already been cleared. The later superblock shutdown path calls sync_filesystem and put_super and dereferences the missing UFS state, causing a kernel oops or panic. For the CVSS the PR:L value is used for the paranoid score because exploitation still requires local access to a delegated mount path, a reduced capability service, or another mechanism that can submit and mount the crafted image. Direct mounting normally requires CAP_SYS_ADMIN and is represented by PR:H in the base score. The issue is not network reachable by itself and does not affect the read only mount path described by this change. Impact is denial of service only because the available code shows a NULL dereference without a UAF, OOB access, information leak, or write primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) SKIP CVE-2026-97927 UNKNOWN SKIP No affected files built, so skip this CVE NO - - unknown MAYBE DISK INIT ERRORPATH UAF LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=0 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=YES NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: -1 * Conservative score: 0 * Raw paranoid score: -1 * Paranoid score: 0 * Applied conservative score-range floor: -1 -> 0 * Applied paranoid score-range floor: -1 -> 0 * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 Reliable kernel crash / strong DoS. A crafted writable UFS image can make cylinder metadata loading fail after `s_root` is published, causing teardown to dereference a NULL `s_fs_info`. * -2 Proven host-admin-equivalent privilege. Directly mounting this UFS image requires host `CAP_SYS_ADMIN`, and UFS is not established as mountable through an attacker-created user namespace. * No corruption bonus. The established primitive is a deterministic NULL dereference, not UAF, OOB access, arbitrary write, double release, or active stale-object use. * No additional Availability point. Kernel Oops or panic is the same consequence already represented by the crash point. * No filesystem integrity point. The defect crashes during failed mount teardown but does not demonstrate persistent filesystem or storage metadata corruption. * No confidentiality or integrity points. There is no disclosure, unauthorized modification, or ownership violation. * No local-unprivileged point. A delegated automount or image-mounting service that exposes the complete operation to an ordinary user is not established. * No remote point. Network input does not directly reach this path. * No race penalty. This is a deterministic initialization and unwind ordering defect, not a timing race. * No niche-subsystem penalty. UFS being specialized is not independently counted because the host-admin mount restriction already captures the material reachability limitation. 3. Reachability analysis The attacker must provide a malformed UFS image and cause a writable mount whose first cylinder group cannot be read. Creating the image is unprivileged, but the complete vulnerable operation is the UFS mount itself. Direct mounting requires host-admin-equivalent `CAP_SYS_ADMIN`. The supplied evidence does not establish a user-accessible privileged mount service, removable-media policy, or another delegated interface that would let a lower-privileged attacker complete the operation. UFS is not shown to support unprivileged mounting through an attacker-created user namespace, so the complete trigger is not namespace-scoped. No network exposure, special hardware, boot parameter, or race is required. A UFS-capable kernel and a writable mount attempt are required. The read-only mount path described by the patch does not load the cylinder structures at this point and therefore does not reach this failure sequence. 4. Primitive and severity interpretation The exact primitive is publication of a partially initialized superblock followed by a NULL pointer dereference during failed-mount teardown. After `ufs_read_cylinder_structures()` fails, cleanup clears `sb->s_fs_info`, while the previously installed `sb->s_root` causes `generic_shutdown_super()` to invoke operations that dereference `UFS_SB(sb)`. This is invalid-state use classified as CLASS_C. It is not an active structured UAF or fixed stale-storage UAF because no object is used after its lifetime ends. There is no repeated release or refcount mutation. The demonstrated consequence is kernel Oops or panic and host denial of service. Privilege escalation, disclosure, controlled corruption, and persistent storage corruption are unsupported. ImportantCandidate is therefore NO. AutoDowngradeAllowed is YES because no unresolved corruption, ownership, authorization, or lifetime primitive would be lost by treating the issue as an ordinary privileged DoS. 5. One-sentence report phrase A crafted writable UFS image can trigger a NULL pointer dereference during failed mount teardown, but direct exploitation requires host administrative mount privileges and the demonstrated impact is kernel denial of service only. 6. Manual review recommendation NO MANUAL CHECK NEEDED The defect is a host-admin-gated, deterministic NULL dereference with no UAF, memory corruption, authorization bypass, or lower-privileged trigger established. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ufs: create the root dentry after loading cylinder metadata Commit: a9804121d55aaa4319c1cac00b99794aa177dd6a Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a9804121d55aaa4319c1cac00b99794aa177dd6a Commit description: ufs_fill_super() installed sb->s_root before it loaded the cylinder group structures for a writable mount: sb->s_root = d_make_root(inode); ... if (!sb_rdonly(sb)) if (!ufs_read_cylinder_structures(sb)) goto failed; When ufs_read_cylinder_structures() failed, the error path freed the in-core superblock information and set sb->s_fs_info to NULL while sb->s_root stayed installed. get_tree_bdev() then reached deactivate_locked_super(), and because s_root was present, generic_shutdown_super() called sync_filesystem() and the put_super operation. Both dereference UFS_SB(sb), which is now NULL, so a mount that fails only while reading the cylinder groups oopses during teardown. A crafted image whose first cylinder group cannot be read reaches this path. Load the cylinder group metadata first and create the root dentry last, so the superblock is published to the VFS only once it is fully set up. ufs_setup_cstotal() and ufs_read_cylinder_structures() take only the super_block and do not use the root inode, so the reordering is safe. Fixes: 1da177e ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Signed-off-by: Ali Ahmet Memis Link: https://patch.msgid.link/20260801071306.59484-2-ali@iusegentoo.com Reviewed-by: Jan Kara Signed-off-by: Christian Brauner (Amutable) Signed-off-by: Greg Kroah-Hartman Changed files: fs/ufs/super.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=a9804121d55aaa4319c1cac00b99794aa177dd6a ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-97927 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97927 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:L/PR:H/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.5 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: unknown Paranoid ActionableScore: 0 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: LOW KPANIC detected for this report: NO Published priority for this report (same as in Subject): LOW 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).