CVE-2026-98215 selinux: preserve user SID across nested backing files
Local attackers can bypass SELinux access controls on nested overlayfs mounts, potentially gaining unauthorized access to protected resources.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-98215?
CVE-2026-98215 is a vulnerability in Linux, published on 6 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-98215?
How do I fix CVE-2026-98215?
Apply the vendor's patch.
Is CVE-2026-98215 being exploited?
There is no known exploitation of CVE-2026-98215 in the wild and no public exploit code.
Sources
Also known as AZL-106269, BELL-CVE-2026-98215, DEBIAN-CVE-2026-98215, GHSA-4rhv-8vqv-p9w9, UBUNTU-CVE-2026-98215.