Qubes OS Addresses QSB-118 Bug That Could Lead to dom0 Takeover

Qubes OS QSB-118 warns of a vulnerability in the qvm-copy-to-vm tool that, when transferring a file from dom0 to a malicious or already compromised qube, could lead to an arbitrary command being executed in dom0. Qubes OS published the bulletin on August 29, 2026. Dom0 is the most privileged part of the system, so successful exploitation means taking control of Qubes OS.

According to the bulletin, this is not a remote unauthenticated attack. The attacker must control the target qube, and the user must initiate a file copy from dom0 to that qube.

Qubes OS QSB-118: The Problem Is in File Name Processing

The flaw occurs when qvm-copy-to-vm is used from dom0. Through an error message, the target qube can influence the name of the transferred file. Insufficient sanitization leaves shell metacharacters intact.

When opening the error dialog, dom0 then uses the system() function. Such a modified file name can inject a command into the shell call and execute it with dom0 privileges.

This is a serious problem for the Qubes OS security model. The system separates applications and work environments into isolated qubes, while dom0 is intended to remain protected even from compromised qubes. This vulnerability could breach that boundary if the user performs the specified file transfer.

All Releases Are Affected; Fix Prepared for Qubes 4.3

The bulletin states that all Qubes OS releases are affected. For the Qubes 4.3 branch, the fix is included in the qubes-core-dom0-linux package version 4.3.22.

At the time the announcement was published, the package was reportedly moving from the security-testing repository to the stable repository after community testing. It was not independently confirmed whether version 4.3.22 was already available in the stable repository. Users should therefore check the update status of their installation and follow the project’s official announcements.

Qubes OS also states that the qvm-copy-to-vm variant run directly inside a VM is not affected. The risky scenario specifically concerns running the tool from dom0 while copying to a target qube controlled by an attacker.

Bulletin Does Not Report Confirmed Exploitation

The materials for Qubes OS QSB-118 do not mention confirmed exploitation of the flaw in the wild. The publication includes PGP signatures whose cryptographic verification was not independently performed by the editorial team.

Further developments will depend mainly on the availability of the patched package in the stable repository, any recommendations for other supported branches, and whether credible information about real-world exploitation emerges.

Verified and updated: August 30, 2026 13:27