Since Tails is based on Debian, it takes advantage of all the work done by the Debian security team. As quoted from https://www.debian.org/security/:

Debian 严肃地看待安全问题, 我们专注地处理任何安全问题 以确保它们能在合理的时间内得到修正。 许多改善建议都会与许多其它自由软件厂商沟通协调, 以便补丁能在漏洞公布的同一时间发布; 我们有安全审计小组来检查存档,以便 找出新的或未修复的安全bug。

Experience has shown that "security through obscurity" does not work. Public disclosure allows for more rapid and better solutions to security problems. In that vein, this page addresses Debian's status with respect to various known security vulnerabilities, which could potentially affect Debian.

Current security vulnerabilities

Fixed security vulnerabilities

Security hole in I2P 0.9.13
Posted

Other vulnerabilities solved in included applications