---
id: "CVE-2026-99052"
kind: "vulnerability"
aliases: ["CVE-2026-99052"]
title: "Linux kernel SELinux: second NFSv4 mount silently disables per-file labeling"
severity: "low"
cvss: null
epss: 0.00209
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["linux-kernel", "nfs", "runtime", "selinux"]
not_affected_if: ["no-nfsv4-security-label", "no-selinux", "single-mount"]
published_at: "2026-10-23T13:17:28+00:00"
first_seen_at: "2026-10-23T21:57:33+00:00"
updated_at: "2026-10-25T12:38:50+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-99052", "first_seen_at": "2026-10-23T21:57:33+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-99052", "first_seen_at": "2026-10-25T12:38:50+00:00"}]
---

# Linux kernel SELinux: second NFSv4 mount silently disables per-file labeling

When an NFSv4 export with security labels is mounted a second time, the kernel's SELinux code fails to flag native labels on the reused superblock, so the NFS client clears the security label capability on the shared server. The result is that per-file SELinux labeling is silently turned off for both mounts.

_Summary, check and fix written by a model from the sources; labelled as such._

## Timeline

- 2026-10-23T21:57:33+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-99052
- 2026-10-25T12:38:50+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-99052

## From the sources

In the Linux kernel, the following vulnerability has been resolved:

selinux: preserve NATIVE_LABELS on already-initialized sb in set_mnt_opts

When an NFSv4 filesystem exported with security_label is mounted a
second time, sget_fc() returns the existing superblock and
nfs_get_root() calls security_sb_set_mnt_opts() again on it. Since the
superblock is already SB_INITIALIZED, selinux_set_mnt_opts() takes an
early exit without setting SECURITY_LSM_NATIVE_LABELS in
*set_kern_flags. nfs_get_root() then sees kflags without
SECURITY_LSM_NATIVE_LABELS set and clears NFS_CAP_SECURITY_LABEL on
the shared nfs_server, silently disabling per-file labeling for both
the new and the original mount.

Commit 3815a245b501 ("security/selinux: fix SECURITY_LSM_NATIVE_LABELS
on reused superblock") fixed the same problem in
selinux_sb_clone_mnt_opts().  The reused-superblock path for a plain
second mount now goes through sb_set_mnt_opts rather than
sb_clone_mnt_opts, so it needs the same treatment: on both
SE_SBINITIALIZED early exits, set SECURITY_LSM_NATIVE_LABELS in
*set_kern_flags when the superblock was already using
SECURITY_FS_USE_NATVE.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_