An anonymous reader writes "vBulletin is a popular proprietary CMS that was recently reported to be vulnerable to an unspecified attack vector. Although vBulletin has not disclosed the root cause of the vulnerability or its impact, we determined the attacker's methods. The identified vulnerability allows an attacker to abuse the vBulletin configuration mechanism in order to create a secondary administrative account. Once the attacker creates the account, they will have full control over the exploited vBulletin application, and subsequently the supported site."