CVE-2026-89766 pidfd: hold exec_update_lock around namespace ioctl

Not scored Published 11 Sep 2026 Updated 19 Oct 2026

A race condition in Linux kernel pidfd namespace ioctls allows local attackers to bypass ptrace access checks and read restricted namespace information.

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-2026-89766?

CVE-2026-89766 is a vulnerability in Linux, published on 11 Sep 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:

pidfd: hold exec_update_lock around namespace ioctl

The PIDFD_GET_*_NAMESPACE ioctls in pidfd_ioctl() perform a filesystem credentials ptrace access check before handing out a namespace file descriptor. The accompanying comment states that the code "mirrors nsfs behavior", but, unlike the corresponding procfs paths, it does so without holding the target task's exec_update_lock.

proc_ns_get_link() and proc_ns_readlink() both take exec_update_lock for reading around the ptrace check and the namespace lookup, so that the credentials used for the access decision match those of the task when its namespace is read. Without it, a caller can pass the check against the target's old credentials and then read the namespace after the target has execve()'d a setuid binary and committed new credentials -- accessing namespace information it should have been denied.

Hold exec_update_lock for reading around the ptrace check and the namespace lookup so that pidfd truly mirrors nsfs behavior, as the comment already claims. open_namespace() itself runs outside the lock: once a namespace reference is obtained it carries its own refcount and is opened with the caller's own credentials, so a concurrent execve() on the target can no longer affect the outcome.

Which versions are affected by CVE-2026-89766?

How do I fix CVE-2026-89766?

Apply the vendor's patch.

Is CVE-2026-89766 being exploited?

There is no known exploitation of CVE-2026-89766 in the wild and no public exploit code.

Sources

Also known as BELL-CVE-2026-89766, DEBIAN-CVE-2026-89766, GHSA-7f3v-362v-5m4g, UBUNTU-CVE-2026-89766.