SFTP Server VM Escape in Canonical Multipass

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Summary

CVECVE-2026-49238
StatePUBLISHED
Assignercanonical
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-28 14:16:24 UTC
Updated2026-05-28 16:16:29 UTC
DescriptionAn 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.

Risk And Classification

Primary CVSS: v3.1 8.4 HIGH from [email protected]

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N

Problem Types: CWE-22 | CWE-22 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary8.4HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N
3.1CNACVSS8.4HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Canonical Multipass affected 1.16.3 semver Not specified

References

ReferenceSourceLinkTags
github.com/canonical/multipass/security/advisories/GHSA-rhp2-23c4-r34w 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis
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