From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-46054][IMPORTANT] selinux: fix overlayfs mmap() and mprotect() access checks Date: Wed, 27 May 2026 11:22:11 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-46054 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: cd0e707a927a70cdfd8bc5a512a9719a87f5ed51 List-Id: CVE: CVE-2026-46054 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: selinux: fix overlayfs mmap() and mprotect() access checks Commit: cd0e707a927a70cdfd8bc5a512a9719a87f5ed51 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cd0e707a927a70cdfd8bc5a512a9719a87f5ed51 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46054 Analysis date: Wed, 27 May 2026 11:22:11 -0400 ActionableScore: 7 ActionableScore lower bound: 5 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: SELinux failed to fully enforce overlayfs backing-file checks for `mmap()` and `mprotect()`, allowing local users with access to an overlay file to potentially bypass lower-file SELinux policy restrictions. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46054 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46054 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-2026-46054 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-284;CWE-863;CWE-266;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N';BEST CVSS score: '6.3';DESCR 'SELinux overlayfs access control for mmap() and mprotect() did not fully enforce checks on the backing file. A local user with access to the visible overlay file could potentially perform mapping or protection changes without the expected SELinux checks against the lower backing file and the mounter credentials. For the CVSS the PR:L is used because the attacker may only need local access to an already mounted overlayfs instance, even though creating the overlay mount is usually privileged. The issue is not network reachable and does not involve UAF, out of bounds access, arbitrary write, or kernel memory corruption. Impact is a SELinux policy bypass with possible confidentiality or integrity impact through unauthorized mapping, execution, or modified executable mapping decisions on backing files.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) YES READ INIT BPF IMPROVEONLY LINUS KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7 NO NO 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 may only need access to an already mounted overlayfs instance and a visible overlay file. * Security-boundary bypass with practical sensitive-object access: +2 The bug bypasses intended SELinux checks for lower backing files during `mmap()` and `mprotect()`. * Cross-boundary isolation/policy bypass: +1 The issue breaks the overlayfs SELinux model that separates user-visible file access from mounter/backing-file access. * Confidentiality impact plausible: +1 Missing backing-file checks may allow unauthorized mapping or reading/executing of lower-file content depending on policy. * Integrity impact plausible: +1 Missing `mprotect()` and executable mapping checks may allow policy-bypassing transitions such as EXECMOD or executable mappings. * Broad/default/common subsystem exposure: +1 SELinux and overlayfs are common in container, distro, and layered filesystem deployments. Subtracting signals: * Configuration/policy dependent: -1 Impact depends on SELinux enforcing mode, overlayfs use, labels, and policy differences between visible overlay files and backing files. Paranoid additional signals: * Sensitive object access concern: +1 In some policies, lower backing files may represent more sensitive objects than the visible overlay labels suggest. * Practical container or namespace policy-bypass concern: +1 Overlayfs is commonly used in container and image-layer workflows, making this access-control bug more actionable than a generic local policy issue. No signals apply for memory corruption, UAF, OOB write, arbitrary write, or remote reachability. ## 3. Reachability analysis The issue is local. The attacker needs access to an overlayfs file and a policy situation where backing-file checks should restrict `mmap()` or `mprotect()` but were not enforced. The attacker does not necessarily need to create the overlay mount if a privileged service, container runtime, or system configuration already provides one. Namespaces and containers are important because overlayfs is common in container stacks. However, the actual impact depends heavily on SELinux policy, labels, mount credentials, and whether lower backing files are more restricted than the user-visible overlay file. ## 4. Severity interpretation This is not memory corruption, but it is a meaningful Linux security-boundary bypass. It should be treated as at least Actionable Moderate and a Strong Important candidate in SELinux/overlayfs-heavy deployments. The realistic impact is unauthorized mapping, execution, or permission transition behavior that SELinux should have blocked. The theoretical impact can include access to sensitive lower-layer content or policy bypass across overlay/container boundaries, but it depends on policy and deployment. ## 5. One-sentence report phrase SELinux failed to fully enforce overlayfs backing-file checks for `mmap()` and `mprotect()`, allowing local users with access to an overlay file to potentially bypass lower-file SELinux policy restrictions. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: this is an access-control and SELinux policy bypass in overlayfs, a real security boundary issue even without memory corruption or remote reachability. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: selinux: fix overlayfs mmap() and mprotect() access checks Commit: cd0e707a927a70cdfd8bc5a512a9719a87f5ed51 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cd0e707a927a70cdfd8bc5a512a9719a87f5ed51 Commit description: The existing SELinux security model for overlayfs is to allow access if the current task is able to access the top level file (the "user" file) and the mounter's credentials are sufficient to access the lower level file (the "backing" file). Unfortunately, the current code does not properly enforce these access controls for both mmap() and mprotect() operations on overlayfs filesystems. This patch makes use of the newly created security_mmap_backing_file() LSM hook to provide the missing backing file enforcement for mmap() operations, and leverages the backing file API and new LSM blob to provide the necessary information to properly enforce the mprotect() access controls. Cc: stable@vger.kernel.org Acked-by: Amir Goldstein Signed-off-by: Paul Moore Signed-off-by: Greg Kroah-Hartman Changed files: security/selinux/hooks.c security/selinux/include/objsec.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=cd0e707a927a70cdfd8bc5a512a9719a87f5ed51 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46054 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46054 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).