Affected: moby

Moby is an open source container framework. In Docker Engine prior to version 29.5.1, Docker Daemon versions 28.5.2 and prior, and Moby Daemon prior to version 2.0.0-beta.14, a race condition during docker cp mount setup allows a malicious container to create empty files or directories at arbitrary absolute paths on the host filesystem. This issue has been patched in Docker Engine version 29.5.1 and Moby Daemon version 2.0.0-beta.14.

Affected: Go: github.com/docker/docker, Go: github.com/moby/moby/v2, Go: github.com/moby/moby

## Summary

A race condition during `docker cp` mount setup allows a malicious container to create empty files or directories at arbitrary absolute paths on the host filesystem.

This advisory covers the race during mountpoint creation. The related race during the subsequent mount syscall is tracked in GHSA-rg2x-37c3-w2rh

## Details

When copying files into a container, the daemon sets up a temporary filesystem view by bind-mounting volumes into a private mount namespace. During this setup, the mount destination path is first resolved within the container's root filesystem using `GetResourcePath`, and then used to create the mountpoint (file or directory) if it does not already exist via `createIfNotExists`.

Between path resolution and mountpoint creation, a process running inside the container can swap a path component for a symlink pointing to an arbitrary location on the host. Because `createIfNotExists` operates on the already-resolved absolute path using standard `os.MkdirAll` and `os.OpenFile` — which follow symlinks in intermediate path components — the symlink is followed and the file or directory is created outside the container root filesystem, as root.

## Impact

A malicious container can create empty files or directories at arbitrary absolute paths on the host filesystem, running as root. This enables persistent denial of service — for example:

- Converting `/etc/docker/daemon.json` into a directory prevents the daemon from restarting - Creating `/etc/nologin…