The warning comes as part of this month's Patch Tuesday where Microsoft released 7 bulletins with fixes for at least 26 documented vulnerabilities affecting the Windows ecosystem.
The company is urging users to pay special attention to MS12-037 and MS12-036, which provides cover for "remote code execution" vulnerabilities that could be used in worm attacks and drive-by downloads without any user interaction.
MS12-037, which affects all supported versions of the IE browser, fixes 13 vulnerabilities that expose users to computer hijack attacks if a user simply surfed to a rigged web site. Microsoft expects to see exploit code targeting at least one of the vulnerabilities within the next 30 days.
The company warned that information on one of the browser flaw is already publicly available which means that hackers have already gotten a head start on preparing attacks.Attack vectors for this issue include maliciously crafted websites and e-mail," the company warned.
This is the second major RPD flaw haunting Windows in the space of a few months.
According to Marc Maiffret, CTO at BeyondTrust, the Internet Explorer and RDP issues present the "more immediate exploitable threats."
"Given the value of Remote Code Execution on RDP there will surely be a lot of folks trying to weaponize that vulnerability. Only time will tell if people are successful with this RDP flaw where they were not with the one in March," Maiffret added.
Windows users and administrators will also want to treat the MS12-038 bulletin with the highest possible priority. From the bulletin:
This security update resolves one privately reported vulnerability in the Microsoft .NET Framework. The vulnerability could allow remote code execution on a client system if a user views a specially crafted webpage using a web browser that can run XAML Browser Applications (XBAPs). Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights. The vulnerability could also be used by Windows .NET Framework applications to bypass Code Access Security (CAS) restrictions.
Microsoft also expects to see exploit code for this vulnerability within the next 30 days.
In addition to the security bulletins, Redmond's security response team is also releasing an automatic updater feature for Windows Vista and Windows 7 untrusted certificates.
The new automatic updater feature provides a mechanism that allows Windows to specifically flag certificates as untrusted.
With this new feature, Windows will check daily for updated information about certificates that are no longer trustworthy. In the past, movement of certificates to the untrusted store required a manual update. This new automatic update mechanism, which relies on a list of untrusted certificates known as a Disallowed Certificate Trust List (CTL), is detailed on the PKI blog. We encourage all customers to install this new feature immediately.
In August, Microsoft is also planning to release a change to how Windows manages certificates that have RSA keys of less than 1024 bits in length. "Once this key length update is released, we will treat all of these certificates as invalid, even if they are currently valid and signed by a trusted certificate authority," Microsoft explained.
These changes follow the incredible discovery that attackers with nation-state backing hacked the Windows Update utility to spoof certificates and spread the Flame malware within Windows networks.