CVE-2026-53341 fhandle: fix UAF due to unlocked ->mnt_ns read in may_decode_fh()
A race condition in the Linux kernel's fhandle subsystem allows a use-after-free, potentially causing a kernel crash or minor information leak.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-53341?
CVE-2026-53341 is a high-severity use after free vulnerability in Linux kernel, published on 1 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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.
Weakness: CWE-416
Which versions are affected by CVE-2026-53341?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-53341?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-53341 being exploited?
There is no known exploitation of CVE-2026-53341 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-53341, DEBIAN-CVE-2026-53341, GHSA-r4cc-8gxc-2cxh, ROOT-OS-DEBIAN-13-CVE-2026-53341, UBUNTU-CVE-2026-53341.