What kind of vulnerability is it?
Anytime a 5xx error is triggered, the auth cookie and other header values are recorded in Jupyter Server logs by default. Considering these logs do not require root access, an attacker can monitor these logs, steal sensitive auth/cookie information, and gain access to the Jupyter server.
Has the problem been patched? What versions should users upgrade to?
Upgrade to Jupyter Server version 1.15.4
For more information
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Credit: @3coins for reporting. Thank you!