SFTP Server VM Escape in Canonical Multipass

{
  "id": "6d53a1bc9f70ac38c79120f0074c7be2163e59ed99807083c82374b408417821",
  "url": "https://osv.dev/vulnerability/CVE-2026-49238",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "SFTP Server VM Escape in Canonical Multipass",
    "summary": "An issue was discovered in Canonical Multipass before version 1.16.3. The host-side SFTP server component (sshfs_server), which executes with root privileges on the host, contains a path containment bypass vulnerability within its validate_path function in src/sshfs_mount/sftp_server.cpp. The function performs a plain string prefix comparison on requested paths without path separator validation or dot-dot (..) normalization. A local attacker with root privileges inside a guest virtual machine can bypass the FUSE layer by injecting raw SFTP frames (such as an SSH_FXP_OPEN request) directly into the sshfs_server process stdin/stdout pipes via procfs. By supplying a path containing directory traversal sequences that match the allowed mount prefix, the attacker can force the host-side root process to resolve the traversal and open files outside the designated mount boundary. This allows a guest-side user to read arbitrary files on the host filesystem, resulting in a virtual machine escape.",
    "evidence": "osv:CVE-2026-49238",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-49238",
      "aliases": [
        "CVE-2026-49238",
        "GHSA-rhp2-23c4-r34w"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/canonical/multipass",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "c8ab690c06ee555de4f5d8659d606d160d29f91e"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "1.16.3"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  },
                  {
                    "cpe": "cpe:2.3:a:canonical:multipass:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "1.16.3"
                      }
                    ],
                    "source": "CPE_RANGE"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v1.16.3-rc1",
            "v1.16.2-rc3",
            "v1.16.2",
            "v1.16.2-rc2",
            "v1.16.2-rc1",
            "v1.16.1-rc3",
            "v1.16.1",
            "v1.16.1-rc2",
            "v1.16.1-rc1",
            "v1.16.0",
            "v1.16.0-rc5",
            "v1.16.0-rc4",
            "v1.16.0-rc3",
            "v1.16.0-rc2",
            "v1.16.0-rc1",
            "v1.15.0-rc1",
            "v1.16.0-dev",
            "v1.14.0-rc1",
            "v1.14.0-rc",
            "v1.15.0-dev",
            "v1.14.0-dev",
            "v1.13.0-rc",
            "v1.12.0-rc",
            "v1.13.0-dev",
            "v1.11.0-rc",
            "v1.12.0-dev",
            "v1.10.0-rc",
            "v1.11.0-dev",
            "v1.9.0-rc",
            "v1.10.0-dev",
            "v1.8.0-rc",
            "v1.9.0-dev",
            "v1.7.0-rc",
            "v1.8.0-dev",
            "v1.7.0-dev",
            "v1.6.0-rc",
            "v1.5.0-rc",
            "v1.6.0-dev",
            "v1.4.0-rc",
            "v1.5.0-dev",
            "v1.4.0-dev",
            "v1.3.0-rc",
            "v1.3.0-dev",
            "v1.2.1",
            "v1.2.0-rc",
            "v1.2.0",
            "v1.1.0-rc",
            "v1.2.0-dev",
            "v1.1.0-dev",
            "v0.10.1-rc",
            "v0.10.0-rc",
            "v0.11.0-dev",
            "v0.9.0-rc",
            "v0.10.0-dev",
            "v0.8.0",
            "v0.9.0-dev",
            "v0.8.0-rc",
            "v0.7.0-rc",
            "v0.8.0-dev",
            "v0.7.0-dev2",
            "v0.6.0-rc",
            "v0.7.0-dev",
            "v0.6.0-pre1",
            "v0.5",
            "2018.12.1-rc1",
            "2018.11.1-pre3",
            "2018.11.1-pre2",
            "2018.11.1-pre1",
            "2018.10.1",
            "2018.4.2",
            "2018.4.1",
            "2017.2.3",
            "2017.2.1"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-49238.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:41.204275239Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/49xxx/CVE-2026-49238.json",
        "https://github.com/canonical/multipass/security/advisories/GHSA-rhp2-23c4-r34w",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-49238"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-22"
        ],
        "cna_assigner": "canonical",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/49xxx/CVE-2026-49238.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-49238",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 509035,
  "published_at": "2026-05-28T13:22:25.529+00:00"
}