From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98214][MODERATE 7.0] selinux: recheck intermediate backing files on mprotect() Date: Fri, 09 Oct 2026 04:32:49 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98214 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: 5 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 4d50ebe5a27724e020747ffd61a051dec67cb8ec List-Id: CVE: CVE-2026-98214 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: selinux: recheck intermediate backing files on mprotect() Commit: 4d50ebe5a27724e020747ffd61a051dec67cb8ec Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4d50ebe5a27724e020747ffd61a051dec67cb8ec Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98214 Analysis date: Fri, 09 Oct 2026 04:32:49 -0400 ActionableScore: 5 ActionableScore lower bound: unknown 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-2026-98214 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98214 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-2026-98214 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98214 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE_KPANIC RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:H/A:L';CWE-863;CWE-284;CWE-693;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N';BEST CVSS score: '5.8';DESCR 'SELinux mprotect checks can be bypassed for intermediate layers of a nested stacked filesystem because the final VMA retains only the lowest backing file. A local process can first map a file with mmap(PROT_NONE) and then request executable permissions with mprotect(PROT_EXEC), while the intermediate mounter SID and file permissions are not rechecked. This can allow execution that the SELinux policy explicitly denies for an intermediate overlayfs layer. For the CVSS the PR:L is selected because an unprivileged local process can invoke mmap and mprotect when a suitable nested filesystem stack is already available, although creating that stack may require stronger privileges. AC:H reflects the need for nested backing files, a specific SELinux policy, and an accessible file with conflicting intermediate permissions. The issue is not directly network reachable. Impact is an SELinux authorization bypass with possible integrity impact and policy dependent privilege escalation. Limited confidentiality or availability impact is plausible in a permissive target policy, but no kernel memory corruption primitive is present.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE READ INIT NOMEMCHK IMPROVEONLY LINUS KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=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: 5 * Paranoid score: 5 * No floor or cap was applied. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown * +2 Concrete authorization decision bypass. Direct `mmap(PROT_EXEC)` is denied by SELinux, while `mmap(PROT_NONE)` followed by `mprotect(PROT_EXEC)` incorrectly succeeds because intermediate backing-layer checks are skipped. * +1 Local unprivileged trigger. Once an accessible nested filesystem stack exists, an ordinary process can invoke `mmap()` and `mprotect()` without host-admin privilege. * +1 Practical exploit chain. The commit demonstrates a complete permission-bypass sequence resulting in an executable mapping that policy explicitly denies. * +1 Central authorization hook fan-out. The affected SELinux `mprotect` hook governs executable, writable, readable, and `execmod` mapping permissions, and the visible fix restores checks for every intermediate backing layer. * No negative privilege point. Host-admin privilege is needed to provision SELinux policy and usually the nested mount topology, but it is not required by the process exercising the vulnerable mapping transition. * No race or timing penalty. The bypass is deterministic. * No separate security-boundary-access +2 was added because that would duplicate the concrete authorization bypass and demonstrated denied-to-allowed mapping. * No confidentiality, arbitrary-write, memory-corruption, UAF, or privilege-escalation points were awarded. * B5-R does not apply. There is no heap OOB write, retry-accumulated index, or later consumption of corrupted heap state. 3. Reachability analysis The evaluated attacker is an ordinary local process that can access a file through an existing nested stacked filesystem. The attacker maps it with `PROT_NONE` and subsequently requests `PROT_EXEC` through `mprotect()`. The nested overlayfs topology and enforcing SELinux policy are genuine prior administrative setup requirements. However, the attacker does not need to create or administer them to exercise the bypass once the path is exposed. No capability or namespace-scoped privilege is required for the vulnerable `mmap()` and `mprotect()` sequence, so `HostAdminRequired=NO` and `NamespaceScopedPrivilege=NO`. The issue is not directly network-triggerable, requires no special hardware, and is not timing-dependent. 4. Primitive and severity interpretation The exact primitive is a deterministic SELinux authorization bypass. A mandatory intermediate-layer `FD__USE`, inode permission, `FILE__EXECUTE`, or `FILE__EXECMOD` check is omitted during `mprotect()`, changing an intended DENY decision into ALLOW. This is neither a UAF nor another memory-lifetime defect. There is no stale storage, repeated release, heap corruption, or retry-accumulated OOB write. The demonstrated consequence is acquisition of an executable mapping that SELinux explicitly prohibits. Policy-dependent privilege escalation or a domain-transition consequence is conceivable, but neither is established by the supplied evidence. No sensitive-file theft, root acquisition, kernel read/write primitive, or confidentiality impact is demonstrated. `PrimitiveClass=CLASS_A` is appropriate because a mandatory LSM authorization boundary is concretely bypassed. `ImportantCandidate=YES` and `AutoDowngradeAllowed=NO` follow from that established security-boundary primitive, even though the numeric score remains in the actionable Moderate range pending policy-specific impact analysis. 5. One-sentence report phrase A local process can bypass SELinux checks for intermediate layers of a nested stacked filesystem by mapping a file with PROT_NONE and later enabling execution with mprotect, allowing an executable mapping that the active policy explicitly denies. 6. Manual review recommendation MANUAL CHECK REQUIRED Review the affected SELinux policies, nested overlayfs deployments, executable labels, `execmod` permissions, and possible domain transitions to determine whether the demonstrated execute-policy bypass can expose protected code or enable privilege escalation. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: selinux: recheck intermediate backing files on mprotect() Commit: 4d50ebe5a27724e020747ffd61a051dec67cb8ec Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4d50ebe5a27724e020747ffd61a051dec67cb8ec Commit description: mprotect() can be used to bypass the SELinux checks that mmap() performs against the intermediate layers of a stacked filesystem. mmap() checks every backing layer as the request descends through the stack. mprotect() only has the lowest backing file in vma->vm_file, so it rechecks the top-level user and the lowest mounter, but skips the mounters of every layer in between. With two nested overlayfs mounts and a policy denying mounter_t -> middle_file_t:file { execute }, a direct mmap(PROT_EXEC) is denied: avc: denied { execute } for pid=71 comm="nested_exec" path="/payload" dev="overlay" ino=9 scontext=user_u:base_r:mounter_t tcontext=user_u:object_r:middle_file_t tclass=file permissive=0 while mmap(PROT_NONE) followed by mprotect(PROT_EXEC) succeeds. Preserve each intermediate path, mounter SID and file-description SID in the backing-file security blob, copying the saved entries when another backing layer is opened. Allocate the array only for nested backing files, and release it and the path references in the backing_file_free hook. During mprotect(), recheck fd { use } and the requested inode permissions for every saved mounter, and include the intermediate layers in the execmod checks. Policy for nested stacking may then need to grant intermediate mounters what a direct mmap() already requires, and execmod on intermediate labels for binaries using text relocations. Tested on arm64 QEMU with a small BusyBox initramfs and a purpose-built SELinux policy, on a mainline tree containing commit f2381b5 ("fs: fix user path of nested backing files"). Cc: stable@vger.kernel.org Fixes: 82544d3 ("selinux: fix overlayfs mmap() and mprotect() access checks") Assisted-by: LLM Signed-off-by: Karl Mehltretter Reviewed-by: Stephen Smalley [PM: subject tweak] 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=4d50ebe5a27724e020747ffd61a051dec67cb8ec ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98214 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98214 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:N/I:H/A:N The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:H/A:L The Best / paranoid CVSS score: 5.8 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: 5 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).