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

CVE-2026-98977 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-98977, released October 24, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-98977
- Priority: Routine
- CVSS: 4.2 (Moderate)
- EPSS: 0.0022
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 23, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-98977

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.115-2 | [DEBIAN-CVE-2026-98977](https://patchblox.com/security/data/fix/linux/debian-cve-2026-98977.md) | Oct 24, 2026 |
| Linux | linux Debian 14 | 7.2.11-1 | [DEBIAN-CVE-2026-98977](https://patchblox.com/security/data/fix/linux/debian-cve-2026-98977.md) | Oct 24, 2026 |

---

Data as of 2026-11-08T13:06:02Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

Free to use with attribution: show "Data: Patchblox Patch Radar" with a link to https://patchblox.com/security/patch-radar. Terms, including what needs a written agreement: https://patchblox.com/security/patch-radar/use-the-data

Product names, logos and trademarks shown on Patch Radar belong to their respective owners. They are used only to identify the software each security fix applies to and to help readers find their platform. Their use does not imply any affiliation with, or endorsement by, those owners, and Patchblox is not affiliated with any of them.