From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-46150][IMPORTANT] fanotify: fix false positive on permission events Date: Thu, 28 May 2026 12:19:29 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-46150 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 7 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: 895ebbedf88318607c24acc0f591c74b165e1d0a List-Id: CVE: CVE-2026-46150 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: fanotify: fix false positive on permission events Commit: 895ebbedf88318607c24acc0f591c74b165e1d0a Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=895ebbedf88318607c24acc0f591c74b165e1d0a Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46150 Analysis date: Thu, 28 May 2026 12:19:29 -0400 ActionableScore: 7 ActionableScore lower bound: 5 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A detached fsnotify mark from an unrelated group could cause fanotify permission-event preparation to fail incorrectly, allowing local access to bypass a userspace-enforced file permission policy. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46150 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46150 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: IMPORTANT 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-2026-46150 IMPORTANT CHECK Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N';CWE-863;CWE-284;CWE-362;CWE-367;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N';BEST CVSS score: '6.3';DESCR 'fsnotify permission event preparation could fail on a detached mark that belonged to an unrelated group, causing the current fanotify permission check to be bypassed instead of skipping that unrelated mark. A local user may benefit when accessing a file protected by a fanotify permission policy while another group mark is being removed, although reliable triggering depends on a race with mark detachment. For the CVSS the PR:L is used because the attacker needs local access to the protected object and the relevant filesystem event path, not full administrative privileges. The issue is not network reachable. Impact is a security policy bypass with possible confidentiality or integrity impact for files protected by fanotify based scanners or access-control daemons, with no supported kernel memory corruption or privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) MAYBE DISK SIMPLEFIX LINUS KPANIC INCREASED_TO_MODERATE7_FROM_MODERATE_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=7 ActionableScoreLower=5 ## 1. ActionableScore * Conservative score: 5 * Paranoid score: 7 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Local unprivileged trigger: +1. A local user can access a protected file and trigger the relevant filesystem event path. * Security-boundary bypass with sensitive-object access: +2. The bug can bypass fanotify permission checks, which are commonly used by scanners, DLP agents, sandboxing, and access-control daemons. * Confidentiality impact plausible: +1. Bypassing permission events may allow reads that the fanotify policy would have denied. * Integrity impact plausible: +1. Bypassing permission events may allow writes or modifications that the policy would have denied. * Hard/racy condition: -1. The bypass depends on a race with detached marks from another group. Paranoid additional signals: * Cross-boundary / policy bypass: +1. This can undermine a userspace-mediated security policy boundary. * Practical sensitive-object access concern: +1. If fanotify protects sensitive paths, bypassing the permission event can expose files or operations that policy intended to block. Not counted: * No kernel memory corruption. * No UAF, OOB write, arbitrary write, or information leak from kernel memory. * No direct privilege escalation primitive. * No network reachability. ## 3. Reachability analysis The attacker is local and needs access to the filesystem object whose access is mediated by a fanotify permission group. The vulnerable condition occurs when an unrelated group has a detached mark that causes `fsnotify_get_mark_safe()` to fail, and the code treats that as a failure of the current permission group rather than skipping it. Namespaces and containers matter because fanotify-based security policies may be used around container or sandbox file access. The attacker does not need to be root, but reliable exploitation depends on racing mark detachment and the protected access. ## 4. Severity interpretation This is an actionable Moderate at minimum and a Strong Important candidate where fanotify is used as an access-control boundary. The key issue is not memory safety but a permission-check bypass. The realistic impact depends heavily on deployment. If fanotify is only used for observation, severity is lower. If it enforces file access policy, confidentiality and integrity impact can be significant. ## 5. One-sentence report phrase A detached fsnotify mark from an unrelated group could cause fanotify permission-event preparation to fail incorrectly, allowing local access to bypass a userspace-enforced file permission policy. ## 6. Manual review recommendation MANUAL CHECK REQUIRED This is a potential access-control bypass. Review is required to determine whether fanotify permission events are used for security enforcement in the affected environment. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: fanotify: fix false positive on permission events Commit: 895ebbedf88318607c24acc0f591c74b165e1d0a Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=895ebbedf88318607c24acc0f591c74b165e1d0a Commit description: fsnotify_get_mark_safe() may return false for a mark on an unrelated group, which results in bypassing the permission check. Fix by skipping over detached marks that are not in the current group. CC: stable@vger.kernel.org Fixes: abc7757 ("fsnotify: Provide framework for dropping SRCU lock in ->handle_event") Signed-off-by: Miklos Szeredi Link: https://patch.msgid.link/20260410144950.156160-1-mszeredi@redhat.com Signed-off-by: Jan Kara Signed-off-by: Greg Kroah-Hartman Changed files: fs/notify/fsnotify.c fs/notify/mark.c include/linux/fsnotify_backend.h 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=895ebbedf88318607c24acc0f591c74b165e1d0a ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46150 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46150 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:H/PR:L/UI:N/S:U/C:L/I:L/A:N The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N The Best / paranoid CVSS score: 6.3 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: IMPORTANT KPANIC detected for this report: YES Published priority for this report (same as in Subject): IMPORTANT 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).