Microsoft warns of 'man-in-the-middle' VPN password hack
'Not a security vulnerability that requires a security update,' says company
Computerworld - Microsoft yesterday warned Windows users of possible "man-in-the-middle" attacks able to steal passwords for some wireless networks and VPNs, or virtual private networks.
It won't issue a security update for the problem, however.
In a blog post written shortly after his Defcon talk, Marlinspike explained his interest in MS-CHAP v2 (Microsoft Challenge Handshake Authentication Protocol version 2). "Even as an aging protocol with some prevalent criticism, it's still used quite pervasively," Marlinspike said. "It shows up most notably in PPTP VPNs, and is also used quite heavily in WPA2 Enterprise environments."
At the same time, Marlinspike published "Chapcrack," a tool that parses data for passwords encrypted with MS-CHAP v2, then decodes them using the CloudCracker password cracking service.
Microsoft acknowledged the threat. "An attacker who successfully exploited these cryptographic weaknesses could obtain user credentials," the Monday advisory stated. "Those credentials could then be re-used to authenticate the attacker to network resources, and the attacker could take any action that the user could take on that network resource."
MS-CHAP v2 is used to authenticate users in PPTP-based (Point-to-Point Tunneling Protocol) VPNs. Windows includes a built-in implementation of PPTP.
To use Chapcrack, an attacker must first capture data packets being transmitted over a VPN or Wi-Fi. The most likely scenario: Spoofing a legitimate wireless hotspot, say at an airport, to sniff out VPN or other traffic, then grab it out of the air.
But Microsoft won't ship an update to fix the problem. "This is not a security vulnerability that requires Microsoft to issue a security update," Monday's advisory read. "This issue is due to known cryptographic weaknesses in the MS-CHAP v2 protocol and is addressed through implementing configuration changes."
Instead, Microsoft recommended that IT administrators add PEAP (Protected Extensible Authentication Protocol) to secure passwords for VPN sessions. A support document described how to configure servers and clients for PEAP.
As Marlinspike noted, MS-CHAP v2, which harks back to Windows NT SP4 and Windows 98, has been denounced as insecure for years, primarily because it's been vulnerable to "dictionary" attacks, where hackers try large numbers of possible passwords.
Windows 7 supports MS-CHAP v2, as does Windows XP and Vista, and Windows Server 2003, Server 2008 and Server 2008 R2.
MS-CHAP v2 cracking tools go back at least to 2007 with the publication of AsLEAP 2.1.
Microsoft said it had not seen any in-the-wild attacks using Marlinspike's Chapcrack.
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, on Google+ or subscribe to Gregg's RSS feed . His email address is firstname.lastname@example.org.
Read more about Cybercrime and Hacking in Computerworld's Cybercrime and Hacking Topic Center.
- Step Out of the Bull's-Eye Learn about the evolution of targeted attacks, the latest in security intelligence, and strategic steps to keep your business safe.
- Using Cyber Insurance and Cybercrime Data to Limit Your Business Risk This paper examines the challenges of understanding cyber risks, the importance of having the right cyber risk intelligence, and how to use this...
- 5 Tips to Secure Small Business Backdoors in the Enterprise Supply Chain This paper examines the insecurity of the small businesses in the supply chain and offers tips to close those backdoors into the enterprise.
- Comprehensive Advanced Threat Defense The hot topic in the information security industry these days is "Advanced Threat Defense" (ATD). This paper describes a comprehensive, network-based approach to...
- Live Webcast Security Vulnerabilities Associated With Having Local Administrator Privileges Viewfinity will demonstrate how removing admin rights and granularly managing privileges at the application level reduces the attack surface.
- Security Vulnerabilities Associated With Having Local Administrator Privileges Viewfinity will demonstrate how removing admin rights and granularly managing privileges at the application level reduces the attack surface.
- Keep Servers Up and Running and Attackers in the Dark An SSL/TLS handshake requires at least 10 times more processing power on a server than on the client. SSL renegotiation attacks can readily... All Cybercrime and Hacking White Papers | Webcasts