CVE-2026-98215: Linux Vulnerability

Description

In the Linux kernel, the following vulnerability has been resolved: selinux: preserve user SID across nested backing files SELinux saves the user file SID in a backing-file security blob so it remains available after mmap() replaces vma->vm_file with a backing file. For nested backing files (overlayfs over overlayfs, or FUSE passthrough backed by overlayfs), user_file may itself be a backing file. Its fsec->sid is the SID of the mounter that opened it, rather than the user that opened the top-level file. mprotect() then checks fd { use } against the mounter SID. This can incorrectly deny access without a domain transition, or check the wrong target SID after one. Copy the saved user SID when user_file is a backing file. Keep using the regular file SID for the first backing layer. With two nested overlayfs mounts and SELinux enforcing, mprotect(PROT_READ) returns EACCES with an fd { use } denial against the mounter SID. With this change, mprotect() succeeds. Tested on arm64 QEMU with a small BusyBox initramfs and a purpose-built SELinux policy. The original test was also repeated with Fedora Cloud Base 44 userspace and gave the same result.

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= bc6c380c1159de52a252ed11f19a42c47f60a735, < caa1b913d90d5dc07073733326d2af0f0288f089; >= 8bacd09f12c27710228562e4d13163e58c5f4a45, < 6aaeec59aadcd1eafc18b049f1b759fb6b9d9569; >= d844702198395d3f80222777030f69db6be6b709, < 9d99b770e7b67b00bdef9005b928aad13e1d679b; >= 82544d36b1729153c8aeb179e84750f0c085d3b1, < ff20d16b2e8230c034e21540043df47222dcc09b; >= 82544d36b1729153c8aeb179e84750f0c085d3b1, < 8c0c602202b9a4909b00bc3354e3c0355bc69e65; cd0e707a927a70cdfd8bc5a512a9719a87f5ed51; >= 6.6.144, < 6.6.158; >= 6.12.95, < 6.12.112; >= 6.18.38, < 6.18.54; >= 7.0.4, < 7.1
Linux	Linux	7.1

References

Timeline

Published: Oct 6, 2026
Last Modified: Oct 6, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-98215?

In the Linux kernel, the following vulnerability has been resolved: selinux: preserve user SID across nested backing files SELinux saves the user file SID in a backing-file security blob so it remains available after mmap() replaces vma->vm_file with a backing file. For nested backing files (overlayfs over overlayfs, or FUSE passthrough backed by overlayfs), user_file may itself be a backing file. Its fsec->sid is the SID of the mounter that opened it, rather than the user that opened the top-level file. mprotect() then checks fd { use } against the mounter SID. This can incorrectly deny access without a domain transition, or check the wrong target SID after one. Copy the saved user SID when user_file is a backing file. Keep using the regular file SID for the first backing layer. With two nested overlayfs mounts and SELinux enforcing, mprotect(PROT_READ) returns EACCES with an fd { use } denial against the mounter SID. With this change, mprotect() succeeds. Tested on arm64 QEMU with a small BusyBox initramfs and a purpose-built SELinux policy. The original test was also repeated with Fedora Cloud Base 44 userspace and gave the same result.

How severe is CVE-2026-98215?

Severity scoring for CVE-2026-98215 is pending analysis.

How do I fix CVE-2026-98215?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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