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Windows XP Zero-Day Vulnerability Popular

Attackers use malicious PDF documents to exploit bug in Windows XP and Windows Server 2003 and take full control of vulnerable systems.

Microsoft is warning that in-the-wild attacks have been spotted that exploit a previously unknown vulnerability in multiple versions of the Windows operating system.

The zero-day vulnerability, dubbed CVE-2013-5065, affects Windows XP SP2 and SP3, as well as Server 2003 SP2, and allows attackers to gain escalated Windows privileges.

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According to Symantec, exploits that target the vulnerability first appeared at the beginning of November. "The attack arrives as a malicious PDF file with file names such as syria15.10.pdf or Note_¹107-41D.pdf, likely by an email attachment, although there is a possibility that targeted users are being enticed to download the malicious file from a website prepared by the attacker," reads a blog post from Symantec.

"Upon successful exploitation of the vulnerability, another malicious file, observed since mid-October, is dropped onto the compromised computer," Symantec said. That malware -- a Trojan known as Wipbot, although some other versions may be detected as Pidief or Suspicious.Cloud.7.F -- forwards information about infected systems to a command-and-control (C&C) server run by attackers.

[ When it comes to zero-day attacks, patching is no longer enough. Read Zero-Day Drive-By Attacks: Accelerating & Expanding. ]

To date, according to Symantec, a "small number" of infected systems have been seen predominantly in India, followed -- in order of severity -- by Australia, the United States, Chile, Hungary, Germany, Norway, and Saudi Arabia.

If the vulnerability is successfully exploited, an attacker could take full control of a system. "An attacker who successfully exploited this vulnerability could run arbitrary code in kernel mode," reads a security advisory from Microsoft. "An attacker could then install programs; view, change, or delete data; or create new accounts with full administrator rights."

The vulnerability has been traced to an input validation error in NDProxy.sys, which is a system-provided driver that interfaces WAN miniport drivers, call managers, and miniport call managers to the Telephony Application Programming Interface (TAPI) services, according to Microsoft.

To exploit the bug, however, an attacker must first gain local access to a system, and to do that, the attacks seen to date have first exploited an Adobe Reader vulnerability. Thankfully, however, the malicious PDF files that have been recovered from active attacks appear to target a vulnerability that's already been patched by Adobe. "The exploit targets Adobe Reader 9.5.4, 10.1.6, 11.0.02, and prior on Windows XP SP3," reads a blog post from researchers at security firm FireEye, which discovered the attacks and reported them to Microsoft. "Those running the latest versions of Adobe Reader should not be affected by this exploit."

Pending a patch from Microsoft, how can information security managers safeguard their systems against attackers using malicious PDF documents to exploit the vulnerability? According to multiple security experts, upgrading to the latest version of Adobe Reader, which is free, or to Microsoft Vista (or newer) or Windows Server 2008 (or newer) will mitigate the vulnerability.

Microsoft said the vulnerability can also be temporarily mitigated by rerouting the NDProxy service to Null.sys. "For environments with non-default, limited user privileges, Microsoft has verified that the... workaround effectively blocks the attacks that have been observed in the wild."

On the downside, however, disabling NDProxy.sys will cause certain services that rely on Windows TAPI to not function, according to Microsoft. That includes remote access service (RAS), dial-up networking, and virtual private networking (VPN).

The vulnerability will likely intensify calls for people to ditch Windows XP in favor of more modern Windows operating systems that are vulnerable to fewer types of attacks like this one.

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