From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74342][MODERATE REGULAR] kernfs: link kn to its parent before the LSM init hook [ Upstream Date: Sun, 16 Aug 2026 00:09:41 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74342 X-AL-KERNEL-Priority: MODERATE REGULAR X-AL-KERNEL-Severity: MODERATE REGULAR X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 4 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: 319b82e8b46edaf557436ad858e734e583f78ec9 List-Id: CVE: CVE-2026-74342 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: kernfs: link kn to its parent before the LSM init hook [ Upstream Commit: 319b82e8b46edaf557436ad858e734e583f78ec9 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=319b82e8b46edaf557436ad858e734e583f78ec9 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74342 Analysis date: Sun, 16 Aug 2026 00:09:41 -0400 ActionableScore: 4 ActionableScore lower bound: 3 Actionable bucket: Borderline, manual review recommended Manual review required: YES Summary: A NULL pointer dereference in kernfs LSM security initialization can panic SELinux-enabled systems during cgroup directory creation because the new kernfs node is used before its parent and root pointers are initialized. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74342 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74342 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 REGULAR 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-2026-74342 MODERATE 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 kernfs can occur because the new kernfs node is passed to the LSM init security hook before kn __parent is linked to the parent and before kn dir root is set. On SELinux enabled systems, selinux_kernfs_init_security can call kernfs_xattr_set and kernfs_root(kn) can resolve to NULL, causing a kernel crash during cgroup directory creation. For the CVSS the PR:L is used for the paranoid score because some deployments delegate cgroup creation or related control plane operations to local non root users or service accounts. The issue is not network reachable and is triggered through local kernfs or cgroup object creation rather than packet traffic. Impact is denial of service via kernel panic. No direct UAF, OOB write, information leak, or privilege escalation primitive is evident from the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 4) SKIP CVE-2026-74342 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 12e9e3cd03b5 YES NO NO unknown MAYBE DANGER NULLPTR DISK INIT DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: 3 * Paranoid score: 4 * Final recommended bucket: **Borderline, manual review recommended**:: ## 2. Signal breakdown Conservative signals: * Reliable kernel crash / strong DoS: +1 The commit shows a deterministic NULL pointer dereference in `simple_xattr_set()` through `kernfs_xattr_set()` on SELinux-enabled systems. * Availability impact realistic: +1 The crash is described as reproducible at PID 1 during early cgroup creation, so the availability impact can be system-wide and boot-impacting. * Broad/default/common subsystem exposure: +1 `kernfs`, cgroups, systemd, and SELinux are common in many enterprise Linux deployments. Paranoid additional signal: * Local unprivileged or reduced-privilege trigger possibility: +1 In some deployments, cgroup creation or cgroup delegation may be exposed to local non-root users, service accounts, container managers, or reduced-capability processes. Signals not awarded: * No generic memory corruption bonus. The demonstrated primitive is a NULL pointer dereference, not UAF, double free, OOB write, type confusion, or controlled overwrite. * No privilege escalation bonus. The patch does not show attacker-controlled reclaim, object replacement, write-after-free, callback control, or another plausible LPE primitive. * No confidentiality or integrity impact. The bug crashes before a useful disclosure or modification primitive is evident. * No remote/network trigger. The path is local kernfs/cgroup creation, not packet processing or remotely reachable protocol handling. ## 3. Reachability analysis The bug is triggered when a new kernfs node is passed to the LSM init security hook before `kn->__parent` and `kn->dir.root` are initialized. On SELinux-enabled systems, `selinux_kernfs_init_security()` may call `kernfs_xattr_set()`, which then calls `kernfs_root(kn)` and dereferences a NULL-derived cache pointer. Typical triggering is local and tied to cgroup or kernfs object creation. In conservative scoring, this is mainly a privileged or system-service path, for example systemd or another cgroup manager. In paranoid scoring, PR:L-like reachability is defensible where cgroup creation is delegated to local users, containers, or service accounts. The bug is not network reachable. ## 4. Severity interpretation This behaves like an actionable Moderate / borderline manual-review issue, not an Important-class memory corruption vulnerability. The realistic impact is deterministic local DoS via kernel panic on SELinux-enabled cgroup setups. The theoretical risk does not extend to LPE based on the patch because there is no UAF, stale object reuse, controlled overwrite, or info leak. The issue should not be treated as a simple low-risk cleanup because it can panic common SELinux systems during normal cgroup creation, including early boot paths. ## 5. One-sentence report phrase A NULL pointer dereference in kernfs LSM security initialization can panic SELinux-enabled systems during cgroup directory creation because the new kernfs node is used before its parent and root pointers are initialized. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Manual review is recommended because the crash is deterministic on common SELinux and cgroup configurations, and some deployments may expose cgroup creation to reduced-privilege local users or service accounts. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: kernfs: link kn to its parent before the LSM init hook [ Upstream Commit: 319b82e8b46edaf557436ad858e734e583f78ec9 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=319b82e8b46edaf557436ad858e734e583f78ec9 Changed files: fs/kernfs/dir.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=319b82e8b46edaf557436ad858e734e583f78ec9 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74342 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74342 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: 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: NO Published priority for this report (same as in Subject): MODERATE REGULAR 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).