This month’s Microsoft patch release is pushed out with lower urgency recommendations overall. While the Sharepoint and server side vulnerabilities are interesting, IT and individuals should attend to the Excel vulnerabilities with urgency. Microsoft is also putting to bed any issues related to Diginotar certificate trust by adding cross signed Diginotar root certificates to the Microsoft Untrusted Certificate Store.
Only five security bulletins are being distributed along with the Diginotar Certificate additions and updates. None are labeled with “Deployment Priority 1”. However, in light of the ongoing spearphishing and targeted attacks, the most relevant and important of these arguably is the Excel related bulletin, MS11-072. While it is being listed as “Important”, not every enterprise has rolled out the latest version of Excel to all of their systems. A set of “use-after-free” and other heap corruption vulnerabilities that are very difficult to discover with automated auditing frameworks plague the application. These vulnerabilities can be exploited to execute spyware, backdoors, and downloaders of the attackers’ choosing on victim systems. Excel related email attachments and links have commonly been used in targeted attacks on organizations and this one should be addressed.
Excel can be a major problem. The RSA breach “2011 Recruitment Plan.xls” file made it very clear how social engineering schemes are used to effectively trick employees – it is important to note that the message was pulled out of the RSA employee’s spam folder and opened. This Excel attachment maintained embedded malicious Flash content and exploited the vulnerability right in front of the employee after being opened, effectively delivering its cyber-espionage payload. Now, attackers don’t need embedded Flash content to take advantage of employee dependency on Excel.