CVE Catalog

CVE-2026-98215

Low risk· EPSS 10%
Published: Updated: Translated: NVD NIST

Exploitation Probability (EPSS)

Low risk
0.21%

10th percentile - higher than 10% of all known CVEs

Summary

In the Linux kernel's SELinux module, there is an issue with preserving user SID across nested backing files. For nested backing files (e.g., overlayfs over overlayfs), the user file SID may be the mounter's SID, leading to incorrect access checks during mprotect().

Risk Assessment

The vulnerability could cause incorrect access denials or checking the wrong SID, potentially violating security policy and allowing unauthorized access.

Recommendation

Apply the Linux kernel patch that copies the saved user SID when the user file is a backing file, ensuring correct access checks.

Other vulnerabilities in Linux kernel

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Original NVD description (English source)

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.

Vulnerability data from NVD (NIST) · CISA KEV · EPSS