CVE-2026-98214

Received Received - Intake

BaseFortify

Publication date: 2026-10-06

Last updated on: 2026-10-19

Assigner: kernel.org

Description

In the Linux kernel, the following vulnerability has been resolved: selinux: recheck intermediate backing files on mprotect() 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 f2381b546e7e ("fs: fix user path of nested backing files"). [PM: subject tweak]

CVSS Scores

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Meta Information

Published

2026-10-06

Last Modified

2026-10-19

Generated

2026-10-19

AI Q&A

2026-10-06

EPSS Evaluated

2026-10-18

NVD

CVE-2026-98214

EUVD

EUVD-2026-93142

Affected Vendors & Products

Vendor	Product	Version / Range
Linux	Linux	bc6c380c1159de52a252ed11f19a42c47f60a735
Linux	Linux	8bacd09f12c27710228562e4d13163e58c5f4a45
Linux	Linux	d844702198395d3f80222777030f69db6be6b709
Linux	Linux	82544d36b1729153c8aeb179e84750f0c085d3b1
Linux	Linux	82544d36b1729153c8aeb179e84750f0c085d3b1
Linux	Linux	cd0e707a927a70cdfd8bc5a512a9719a87f5ed51
Linux	Linux	6.6.144
Linux	Linux	6.12.95
Linux	Linux	6.18.38
Linux	Linux	7.0.4
Linux	Linux	7.1

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-UNKNOWN

Attack-Flow Graph

Executive Summary

This vulnerability in the Linux kernel involves a flaw in the SELinux security module where mprotect() can bypass checks performed by mmap() on stacked filesystems. Normally, mmap() verifies permissions at each layer of a stacked filesystem, but mprotect() only checks the top-level user and lowest mounter, skipping intermediate layers. This allows bypassing SELinux policies that restrict execute permissions on nested overlayfs mounts.

Detection Guidance

This vulnerability is specific to the Linux kernel's SELinux implementation and nested filesystem stacking. Detection requires checking kernel logs for SELinux denials related to mprotect() bypass attempts. Look for AVC denials in /var/log/audit/audit.log or dmesg output mentioning execute permissions on intermediate overlayfs layers.

Impact Analysis

An attacker with local access could exploit this to execute unauthorized code by bypassing SELinux restrictions on stacked filesystems. This could lead to privilege escalation or unauthorized access to sensitive data, depending on the system's SELinux policy configuration.

Compliance Impact

This vulnerability could potentially affect compliance with standards like GDPR and HIPAA by allowing unauthorized code execution through bypassing SELinux checks. This may lead to data breaches or unauthorized access, violating confidentiality and integrity requirements in these regulations.

Mitigation Strategies

Apply the latest Linux kernel security patches that address this issue. Update SELinux policies to explicitly deny mprotect(PROT_EXEC) on nested overlayfs mounts. Monitor for any policy changes needed for intermediate layers in stacked filesystems.

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