CVE-2026-49238 Details

A path traversal vulnerability has been identified in Canonical Multipass versions prior to 1.16.3. The issue resides in the host-side SFTP server component, sshfs_server, which runs with root privileges. The vulnerability arises because the validate_path function in src/sshfs_mount/sftp_server.cpp performs a simple string prefix comparison on requested paths without validating path separators or normalizing directory traversal sequences. This flaw allows a local attacker with root access inside a guest virtual machine to bypass the FUSE layer by injecting raw SFTP frames, such as an SSH_FXP_OPEN request, directly into the sshfs_server process's stdin/stdout pipes via procfs. By crafting a path traversal that aligns with the allowed mount prefix, the attacker can manipulate the host-side root process to access files outside the designated mount boundary. This exploitation enables the guest user to read arbitrary files from the host filesystem, resulting in a virtual machine escape.

Users can upgrade to Canonical Multipass version 1.16.3 or later to address this vulnerability.