UPDATE: Tails version 5.1 has been released. Upgrade now.
Tor Browser in Tails 5.0 and earlier is unsafe to use for sensitive information. From the Tails website:
We recommend that you stop using Tails until the release of 5.1 (May 31) if you use Tor Browser for sensitive information (passwords, private messages, personal information, etc.).
This vulnerability allows a malicious website to bypass some of the security built in Tor Browser and access information from other websites.
For example, after you visit a malicious website, an attacker controlling this website might access the password or other sensitive information that you send to other websites afterwards during the same Tails session.
This vulnerability doesn’t break the anonymity and encryption of Tor connections.
Photo by Rubaitul Azad