---
id: CVE-2026-74618
title: >-
  In the Linux kernel, the following vulnerability has been resolved:


  binfmt_misc: don't warn when the mount is completed from another user
  namespace


  fsopen() records the caller's user namespace in fc->user_ns and hands

  back an ordinary …
summary: >-
  In the Linux kernel, the following vulnerability has been resolved:


  binfmt_misc: don't warn when the mount is completed from another user
  namespace


  fsopen() records the caller's user namespace in fc->user_ns and hands

  back an ordinary …
severity: none
published: '2026-08-22'
updated: '2026-10-14'
sourceUpdated: '2026-10-14T13:10:00.187'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-74618'
references:
  - url: 'https://git.kernel.org/stable/c/047f927f54c6c17593e93aafe82dcb7acdda2a71'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/24e95a24f151ce40d5fc1b3a6cefbcda8ded736c'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/37cf5cf1320a84a17225a1690547b8a0812ca94e'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/79fdf39f1a31f88cb3833b6f8091fbf6acdca2c6'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
epss: 0.00168
epssPercentile: 0.05618
ingestedAt: '2026-10-14T13:30:58.517Z'
---

## Overview

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

binfmt_misc: don't warn when the mount is completed from another user namespace

fsopen() records the caller's user namespace in fc->user_ns and hands
back an ordinary file descriptor. Nothing ties the task that calls
fsconfig(FSCONFIG_CMD_CREATE) to the task that created the context. The
fd is inherited across fork() and exec() and it can be passed over a
unix socket.

Completing a context from another user namespace is allowed on purpose.
vfs_cmd_create() authorizes the create with mount_capable(), which for
FS_USERNS_MOUNT checks ns_capable(fc->user_ns, CAP_SYS_ADMIN), and that
succeeds for a task holding CAP_SYS_ADMIN in an ancestor of fc->user_ns.
So an unprivileged task can reach the WARN_ON() in bm_fill_super():
create a user and a mount namespace in a child, call
fsopen("binfmt_misc") there, send the fscontext fd to the parent and let
the parent issue FSCONFIG_CMD_CREATE. Both namespaces come from a plain
unshare(1) and no capability is needed anywhere:

  WARNING: fs/binfmt_misc.c:938 at bm_fill_super+0xa2/0xc0 [binfmt_misc]
  CPU: 15 UID: 1000 PID: 3243382 Comm: fswarn
  Call Trace:
   get_tree_keyed+0x7d/0xb0
   bm_get_tree+0x34/0x90 [binfmt_misc]
   vfs_get_tree+0x2a/0x100
   vfs_cmd_create+0x60/0xf0
   __do_sys_fsconfig+0x4b2/0x500

The child needs the mount namespace because fsopen() itself gates on
may_mount(), which asks for CAP_SYS_ADMIN in the user namespace owning
the caller's mount namespace. fsconfig() doesn't repeat that check.

It is a WARN_ON() and not a WARN_ON_ONCE(), so the condition can be
raised in a loop to taint the kernel and flood the log, and it panics a
kernel booted with panic_on_warn.

Keep refusing the mount and stop warning about it. Nothing in
bm_fill_super() depends on the two namespaces matching, it derives
everything from sb->s_user_ns.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.