Why use Qubes over other Virtualizers?
Why use Qubes over other Virtualizers?
The Qubes project is focused on developing the Qubes OS desktop operating system, which is based upon the principle of "Security by Isolation". It is not a general purpose operating system where the ability to install a virtualizer is just another feature. Rather, it runs a bare-metal virtualizer (Xen) and isolates hardware controllers and multiple user domains (qubes) in separate VMs that are explicitly assigned different levels of trust.
Advanced Separation / Least Privilege
- The Xen hypervisor and administrative domain (
dom0) in Qubes OS actively discourages any activity other than running VMs.
- The network stack and WiFi drivers are running in a dedicated, unprivileged network qube (NetVM), which substantially reduces the attack surface.
- Future separation of the GUI (graphical) domain from
dom0is partially implemented in Qubes
Hardware and Protocol Protection
- Enabling VT-d/IOMMU via BIOS provides DMA protection.
- The USB stack can be isolated in a dedicated USB VM, protecting
dom0from untrusted USB devices.
- Anti Evil Maid (AEM) protection is supported.
- Yubikey multi-factor user authentication is available to enhance the security of logins, mitigate the risk of password snooping, and improve USB keyboard security.
- No microphones are attached to VMs by default.
- An additional firewall VM is used to house the Linux kernel-based firewall, providing extra protection against a compromised NetVM; see Qubes networking.
- By default, Qubes OS is firewalled and no incoming ports are open.
- No networking is present in the administrative domain (
dom0upgrades are done in a dedicated UpdateVM (currently set by default to
sys-firewall), before those are verified and installed in
- All Template and
dom0updates can be easily fetched over Tor via the Whonix-Gateway™ ProxyVM (commonly called
- TCP timestamps are disabled by default. 
- ICMP timestamps are disabled by default. 
- Protection against unintentional leaks of critical user data is possible by setting an empty NetVM field for the corresponding qube.
- Tor Traffic can be white-listed using corridor as a filtering gateway, protecting against accidental clearnet leaks.
- Availability of an experimental unikernel firewall based on MirageOS for greater security, performance and a lower resource footprint.
- Disposables are available to open untrusted applications, links, attachments and documents. 
- Service qubes can be configured as a static Disposables to mitigate the threat from persistent malware across VM reboots. 
- Unforgeable, colored window borders allow easy identification of qubes with different security levels.
- PDFs can be easily sanitized via a trusted PDF converter. 
- Greater security of email-centric work environments is possible by using split GPG to protect private keys and limiting network connections exclusively to the chosen email server.
- Joanna Rutkowska, security researcher, founder and developer emeritus of Qubes OS has completed a research paper comparing the security of software compartmentalization vs. physically separated computers (pdf). It concluded that in some cases, notably for specific, desktop-related workflows, Physical Isolation might be less secure than Qubes' compartmentalized approach.
- OS agnostic: qubes can be based upon Fedora, Debian, Ubuntu, Whonix™, Windows, Kali Linux, CentOS and Arch Linux templates, among others.
- All isolated qubes are integrated into a single, usable system via a unified desktop.
- Software installation and updates are centralized.
- Creating new VMs and disposing of unwanted VMs is very easy and fast.
- The VM start menu is integrated into the host's (
dom0) start menu via Qubes VM Manager.
- A secure and usable mechanism exists for copying and pasting clipboard contents and files between qubes.
- An easier backup / restore mechanism for VMs.
- The keyboard layout only needs to be configured once in
- No duplicate task bars are present.
- A default seamless mode is available for Windows (similar to VirtualBox’s Seamless Mode or VMware’s Unity Mode).  It is easy to distinguish which window belongs to each VM. 
- See also: A Usability Evaluation of Qubes OS.
- VMs boot up much faster, because fewer services need to be started.
- App Qubes therefore also use much less RAM.
- App Qubes use far less disk space because they can share the root image of the Template in read-only mode. Separate disk storage is only used for the user's directory and per-VM settings (read more: Template Implementation).
- Standalones can be created for the installation of software in only specific domains.
Qubes-Whonix™ Advantages over Non-Qubes-Whonix
- It is easier to tunnel the whole system -- including host (
dom0) updates -- through Tor (besides
- Multiple Whonix-Workstation App Qubes can easily use the same Whonix-Gateway ProxyVM without being able to make contact with one another. 
- Downloads of Whonix Template images use cryptographic signatures of the
dom0package manager (qubes-dom0-update / dnf). Without the user knowing it, this makes verification transparent.
- It is simple to run Tor Browser in a Whonix-Workstation Disposable.
- Various operations can be securely performed in Qubes-Whonix VMs which are not available in Non-Qubes-Whonix, like:
- Easier installation.
- As an option during Qubes installer.
- Or later downloaded from the Qubes repository.
- Issues specific to Non-Qubes-Whonix do not apply.
- No confusing Network Manager Systray Unmanaged Devices error messages, since there is no duplicate taskbar.
- No confusion is caused by the VM timezone being set to UTC (for anonymity reasons),  since there is no duplicate taskbar. 
Qubes is not however a silver bullet - attacks are still possible against:
- The virtualization technology (VT-x, VT-d).
- The hypervisor (Xen). 
- Additional software used by any virtualized system, like qemu and DirectX emulation.
Further, data leaks are possible via cooperative covert channels (malware working in concert across two or more VMs), and side channel attacks (malware in one VM trying to learn about processes executed in another VM).
- Disable TCP Timestamps.
- Disable ICMP Timestamps.
- From Qubes R4.0, disposable Whonix-Workstation™ VMs are now available, as well as multiple Disposables for other platforms.
sys-usbcan be configured as static Disposables. This option was first made available in Qubes R4.
Convert to Trusted PDF
The minimal templates are lightweight versions of their standard template counterparts. They have only the most vital packages installed, including a minimal X and xterm installation. When properly configured and used, minimal templates can be less resource-intensive, reduce attack surface, and support more fine-grained compartmentalization.
- This issue for Non-Qubes-Whonix is documented on the Multiple Whonix-Workstation wiki page.
Qubes PDF Converter is a Qubes OS application that uses Disposables and Qubes' flexible qrexec (inter-VM communication) infrastructure to securely convert untrusted PDF files into safe-to-view PDF files. This is done by using a Disposable to render each page of a PDF file into a very simple representation (RGB bitmap) that (presumably) leaves no room for malicious code. This representation is then sent back to the client qube which then constructs an entirely new PDF file out of the received bitmaps.
- Converting untrusted PDFs into trusted ones: The Qubes Way.
- Network Time Syncing.
- See: Xen Security Advisories.