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CVE-2026-49238 Canonical CVE debrief

A path containment bypass vulnerability in Canonical Multipass's host-side SFTP server component (sshfs_server) allows a local attacker with root privileges inside a guest virtual machine to read arbitrary files on the host filesystem. The vulnerability exists in the validate_path function in src/sshfs_mount/sftp_server.cpp, which performs a plain string prefix comparison on requested paths without proper path separator validation or dot-dot (..) normalization. An attacker can bypass the FUSE layer by injecting raw SFTP frames directly into the sshfs_server process stdin/stdout pipes via procfs, supplying paths with directory traversal sequences that match the allowed mount prefix. This results in a virtual machine escape with high impact on confidentiality and integrity. The vulnerability affects Multipass versions before 1.16.3.

Vendor
Canonical
Product
Multipass
CVSS
HIGH 8.4
CISA KEV
Not listed in stored evidence
Original CVE published
2026-05-28
Original CVE updated
2026-05-28
Advisory published
2026-05-28
Advisory updated
2026-05-28

Who should care

Organizations running Canonical Multipass for development, testing, or production virtualization workloads should prioritize patching. Security teams managing multi-tenant environments with untrusted guest workloads face elevated risk of VM escape and host compromise. DevOps practitioners using Multipass for CI/CD pipelines should verify instance isolation controls and update promptly.

Technical summary

The sshfs_server component in Canonical Multipass before 1.16.3 contains a path validation flaw in validate_path() that permits directory traversal through crafted SFTP requests. The function's reliance on simple string prefix matching without canonicalization allows attackers with guest root access to inject raw SFTP frames via procfs, bypassing FUSE restrictions and accessing arbitrary host files. The vulnerability is classified as CWE-22 and carries a CVSS 3.1 score of 8.4 (HIGH) with attack vector LOCAL, attack complexity LOW, and scope CHANGED.

Defensive priority

HIGH

Recommended defensive actions

  • Upgrade Canonical Multipass to version 1.16.3 or later to remediate this vulnerability.
  • Restrict access to guest virtual machines to trusted users only, as exploitation requires root privileges inside the guest.
  • Monitor for suspicious procfs access patterns targeting sshfs_server process pipes.
  • Review file system access logs on Multipass host systems for unexpected file access outside designated mount boundaries.
  • Apply principle of least privilege for virtual machine deployments to limit potential impact of guest compromise.

Evidence notes

Vulnerability disclosed via NVD on 2026-05-28 with CVSS 3.1 score 8.4 (HIGH). Official security advisory published by Canonical at GHSA-rhp2-23c4-r34w. CWE-22 (Improper Limitation of a Pathname to a Restricted Directory) identified as the weakness type.

Official resources

2026-05-28