6.x series is vulnerable to CVE-2019-10856

[ist199099]

Describe the bug
The 6.x series are vulnerable to CVE-2019-10856.

To Reproduce
Steps to reproduce the behavior:

1. Set up a notebook server.
2. Construct a link to exploit CVE-2019-10856 and open it in Chrome.
3. Enter a valid username and password and log in.

Expected behavior
The server should refuse to show the login page or to redirect to the malicious website.

[RRosio]

Hi @ist199099, thank you for submitting this issue! The fix for this issue, #6511 was merged in and available the latest release of notebook, 6.5.2. I will close out this issue now, but please feel free to reopen if there is more to address!