Cloudanix VulnDB

CVE-2026-98977

None

CVSS

—

EPSS

0.2%

Published

Oct 23, 2026

CISA due date

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Cloudanix analysis

Schedule a fix SSVC: Track

A recently fixed Linux kernel bug could let programs inside isolated environments change or lock file-system security settings they were never supposed to touch.

Exploitation
Local Privilege
Attacker needs
Local User
Complexity
Moderate
Impact
Privilege Gain
Component
OS kernel
Class
Race Condition
Remediation
Upgrade
Effort
Medium
Patch risk
Medium

What it actually does

Incorrect locking of source mounts during recursive attachment in attach_recursive_mnt() when automounts propagate across user namespaces; the lock is placed on the host/parent copy instead of the namespace-local copy, allowing bind remount flag changes to succeed or fail contrary to policy.

Why it matters to the business

In container, sandbox, or multi-tenant Linux deployments, unprivileged processes may bypass intended mount restrictions or cause host-level mount state to become unchangeable, leading to unexpected privilege escalation paths or operational mount failures within two days of disclosure.

How an attack unfolds

An attacker receives a directory descriptor on a shared debugfs-style mount, enters a user and mount namespace, triggers an automount via path lookup that propagates from the host, then issues a bind remount to clear flags; the misapplied lock permits the child namespace to succeed while the host is denied, or vice versa.

How to fix it

Upgrade to the patched Linux kernel that selects the authoritative mount namespace owner before locking; apply the fix that landed in the stable branches after 2026-10-23.

How to confirm the fix worked

Reproduce the supplied test case (host debugfs shared, child namespace stat on tracefs, bind remount) and confirm that the lock is now applied to the child's copy rather than the host mount.

Typical attack path

  1. Obtain directory file descriptor on a shared mount from the host
  2. Enter a new user and mount namespace
  3. Perform stat or open that triggers automount on the host mount
  4. Issue MS_REMOUNT|MS_BIND to alter flags on the propagated copy
  5. Observe inconsistent permission or lock behavior between host and namespace

How to detect it

Review kernel audit logs and namespace creation events around the same time as mount flag change attempts; correlate with processes entering new user namespaces shortly before automount activity.

What your security team should do

  • Prioritize kernel updates on systems using user namespaces and shared mounts within the next 30 days
  • Audit container runtime configurations that pass directory descriptors across namespace boundaries
  • Enable kernel audit logging of mount and namespace operations for anomaly detection

The record

In the Linux kernel, the following vulnerability has been resolved: namespace: handle mount locking for automounts correctly If mounts are propagated across user namespaces, attach_recursive_mnt() locks every copy of the source mount to protect overmounts from vanishing and revealing the underlying files or directories. The user namespace is taken from the caller's mount namespaces since this is where the mounts end up. Except, that's not always true. Automounts may legitimately get popped in by tasks located in a different mount and user namespace during path lookup. Then check doesn't make sense at that point. The copy in the namespace of the parent - which may be the host's - is now locked and the host cannot change the flags of its own mounts anymore. Here's the reproducer: - host has debugfs mounted nosuid,nodev,noexec and shared - tracefs automount below it is not yet active - hand a child process a directory descriptor on that mount - child process enters auser and mount namespace - child process' namespace now holds a locked copy of the host's debugfs mount that receives propagation from it - child process stats "tracing/." through the descriptor - lookup runs on the host's mount so the automount lands below the host's mount - propagation puts a copy below the child's copy - both try to clear the flags on the mount they got, with a bind remount: host, on its own automount: MS_REMOUNT|MS_BIND = EPERM child, on the copy in its namespace: MS_REMOUNT|MS_BIND = 0 So the lock landed on the host's mount instead of the child's copy. Congrats. So we need to compare with the owner of the namespace the mount actually gets mounted on. For all regular cases that is the caller's mount namespace and so nothing changes. Detached trees in anonymous mount namespaces by be handed over via SCM_RIGHTS or inherited in other ways on purpose so the attaching task's mount namespace is authoritative, not the creator of the detached tree.

Affected packages

Ecosystem Package Introduced Fixed