Summary
Arbitrary command execution on Windows via qutebrowserurl: URL handler
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.
Timeline
2021-10-15: Issue reported via [email protected] by Ping Fan (Zetta) Ke of Valkyrie-X Security Research Group (VXRL)
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 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 (VXRL/@vxresearch) for finding and responsibly disclosing this issue.
Contact
If you have any questions or comments about this advisory, please email [email protected].
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.
Untrusted input is inserted into a command that is later executed by the application, allowing the attacker to alter the intent of that command. Typical impact: arbitrary command execution in the application's environment.
CVE-2021-41146 has a CVSS score of 8.8 (High). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.4.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
The issue has been fixed in qutebrowser 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)
Frequently Asked Questions
- What is CVE-2021-41146? CVE-2021-41146 is a high-severity command injection vulnerability in qutebrowser (pip), affecting versions >= 1.7.0, < 2.4.0. It is fixed in 2.4.0. Untrusted input is inserted into a command that is later executed by the application, allowing the attacker to alter the intent of that command.
- How severe is CVE-2021-41146? CVE-2021-41146 has a CVSS score of 8.8 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of qutebrowser are affected by CVE-2021-41146? qutebrowser (pip) versions >= 1.7.0, < 2.4.0 is affected.
- Is there a fix for CVE-2021-41146? Yes. CVE-2021-41146 is fixed in 2.4.0. Upgrade to this version or later.
- Is CVE-2021-41146 exploitable, and should I be worried? Whether CVE-2021-41146 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2021-41146 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2021-41146? Upgrade
qutebrowserto 2.4.0 or later.