... On April 5th, the attackers via a compromised Slicehost server opened a new issue, INFRA-2591. This issue contained the following text:
ive got this error while browsing some projects in jira http://tinyurl.com/XXXXXXXXX [obscured]
Tinyurl is a URL redirection and shortening tool. This specific URL redirected back to the Apache instance of JIRA, at a special URL containing a cross site scripting (XSS) attack. The attack was crafted to steal the session cookie from the user logged-in to JIRA. When this issue was opened against the Infrastructure team, several of our administators clicked on the link. This compromised their sessions, including their JIRA administrator rights. ...
If I understand the rest of it correctly, the administrators didn't have to be logged in as root for this attack to succeed. Sudo was used by the attackers to gain root access.