phpbb -- arbitrary command execution and other vulnerabilities

The ChangeLog for phpBB 2.0.11 states:

Changes since 2.0.10

• Fixed vulnerability in highlighting code (very high severity, please update your installation as soon as possible)
• Fixed unsetting global vars - Matt Kavanagh
• Fixed XSS vulnerability in username handling - AnthraX101
• Fixed not confirmed sql injection in username handling - warmth
• Added check for empty topic id in topic_review function
• Added visual confirmation mod to code base

[source]

Additionally, a US-CERT Technical Cyber Security Alert reports:

phpBB contains an user input validation problem with regard to the parsing of the URL. An intruder can deface a phpBB website, execute arbitrary commands, or gain administrative privileges on a compromised bulletin board.

[source]