OSSA-2021-002: Open Redirect in noVNC proxy


July 29, 2021




  • Nova: <21.2.3, >=22.0.0 <22.2.3, >=23.0.0 <23.0.3


Swe Aung, Shahaan Ayyub, and Salman Khan with the Monash University Cyber Security team reported a vulnerability affecting Nova’s noVNC proxying implementation which exposed access to a well-known redirect behavior in the Python standard library’s http.server.SimpleHTTPRequestHandler and thus noVNC’s WebSockifyRequestHandler which uses it. By convincing a user to follow a specially-crafted novncproxy URL, the user could be redirected to an unrelated site under control of the attacker in an attempt to convince them to divulge credentials or other sensitive data. All Nova deployments with novncproxy enabled are affected.


The initial fix did not take into account the possibility of bypass using exactly three slashes. This update provides a more thorough revised fix for the issue. The affected versions list has been updated to indicate versions expected to include the newer solution.



  • Swe Aung from Monash University Cyber Security team (CVE-2021-3654)

  • Shahaan Ayyub from Monash University Cyber Security team (CVE-2021-3654)

  • Salman Khan from Monash University Cyber Security team (CVE-2021-3654)



  • The stable/train branch is under extended maintenance and will receive no new point releases, but a patch for it is provided as a courtesy.

OSSA History

  • 2021-09-27 - Errata 1

  • 2021-07-29 - Original Version