Starting with qutebrowser v1.7.0, the Windows installer for qutebrowser registers it as a handler for certain URL schemes. With some applications such as Outlook Desktop, opening a specially crafted URL can lead to argument injection, allowing execution of qutebrowser commands, which in turn allows arbitrary code execution via commands such as :spawn or :debug-pyeval.
Only Windows installs where qutebrowser is registered as URL handler are affected. It does not have to be set as default browser for the exploit to work.
The fix also adds additional hardening for potential similar issues on Linux (by adding the new --untrusted-args flag to the .desktop file), though no such vulnerabilities are known.