CVE-2021-41146

### Impact 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. ### Patches The issue has been fixed in [qutebrowser v2.4.0](https://github.com/qutebrowser/qutebrowser/releases/tag/v2.4.0) in commit 8f46ba3f6dc7b18375f7aa63c48a1fe461190430. 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. Backported patches for older versions are available, but no further releases are planned: - v1.7.x: d1ceaab - v1.8.x: ca7155d - v1.9.x: 157d871 - v1.10.x: 94a6125 - v1.11.x: 10acfbb - v1.12.x: 363a18f - v1.13.x: 410f262 - v1.14.x: e4f4d93 - v2.0.x: 15a1654 - v2.1.x: 509ddf2 - v2.2.x: 03dcba5 - v2.3.x: 00a694c (commits are referring to qutebrowser/qutebrowser on GitHub) ### Workarounds Remove qutebrowser from the default browser settings entirely, so that it does not handle any kind of URLs. Make sure to remove *all* handlers, including an (accidental) `qutebrowserURL` handler, e.g. using [NirSoft URLProtocolView](https://www.nirsoft.net/utils/url_protocol_view.html). ### Timeline 2021-10-15: Issue reported via security@qutebrowser.org by Ping Fan (Zetta) Ke of [Valkyrie-X Security Research Group (VXRL)](https://www.vxrl.hk/) 2021-10-15: Issue confirmed by @The-Compiler (lead developer), author of installer (@bitraid) contacted for help/review 2021-10-15: CVE assigned by GitHub 2021-10-15 to 2021-10-17: Fix developed 2021-10-17: Additional core developer (@toofar) contacted for help/review 2021-10-21: v2.4.0 released containing the fix 2021-10-21: Advisory and fix published ### References See the [commit message](https://github.com/qutebrowser/qutebrowser/commit/8f46ba3f6dc7b18375f7aa63c48a1fe461190430) for additional information and references to various similar issues in other projects. ### Acknowledgements Thanks to Ping Fan (Zetta) Ke of [Valkyrie-X Security Research Group](https://www.vxrl.hk/) (VXRL/@vxresearch) for finding and responsibly disclosing this issue. ### Contact If you have any questions or comments about this advisory, please email [security@qutebrowser.org](mailto:security@qutebrowser.org).

qutebrowser is an open source keyboard-focused browser with a minimal GUI. Starting with qutebrowser v1.7.0, the Windows installer for qutebrowser registers a `qutebrowserurl:` URL handler. With certain applications, opening a specially crafted `qutebrowserurl:...` URL can lead to 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. The issue has been fixed in qutebrowser v2.4.0. 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.