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Setting up VPN connection: After some more trying and looking on the web, I managed to make the VPN connection by the following steps: Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. Post Your Answer Discard By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service , privacy policy and cookie policy , and that your continued use of the website is subject to these policies.
It is possible there is a registry hack, or some hot-fix that was missed that may be available to fix this exploit, however I was not able to find such a fix that actually worked. Several were related, but after applying them, the systems were still vulnerable to this attack. The most basic passive mode simply "sniffs" the traffic from a PPTP challenge-response event, it parses out the MS-CHAP portion and outputs the information to any file in a format compatible with the L0phtcrack password cracking tool.
The user will then see a password change request dialog box appear on the screen. The user will then fill it out and submit the information, then the attacker will easily acquire this information. These hashes will then be formatted and output to a L0phtcrack compatible file for cracking.
Though these experiment were performed mostly on hubs using Ethereal, I did perform some tests using dsniff on the switch and was able to grab similar information. So it is certainly possible to perform this same attack on switched networks. It was a trivial effort to capture and parse and break the LANMAN hashes, with enough modifying of the scripts and tying them together, it could possibly be performed in seconds instead of minutes.
Signature of the attack: However, the new encryption methods used do not provide any significant security improvement in preventing the easily sniffed NT Encryption hashed challenge-response information from being almost as easily parsed, and broken quickly with L0phtcrack and similar tools. The same as Attack 4, a NIC in promiscuous mode could be a warning sign.
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Strong passwords that are not dictionary based will be much more resistant to such attacks, if even one user password is dictionary based, then it is likely an attacker will crack it in time, and possibly fast enough to compromise the infrastructure. In this section we will go into non-implementation specific descriptions of the protocols covered in this document. Implementation specific versions of these protocols will be covered later. RFC http: A tunnel must be established between each pair and a key that is included in the GRE packet header lists which tunnel session a PPP packet is a memoryber of.
The Control Connection actually determines the rate and traffic congestion actions based on information from these GRE headers. PPTP does not itself specify which algorithms or technologies to use for congestion-control and flow-control though some are suggested , rather that is left open to the implementer to determine, but again, using the information from the GRE headers as the data to act against for adjustments.
A very brief summary follows:. CHAP is used during the initial connection and might be repeated occasionally throughout the session to verify identity. RFC Abstract: A very brief summary of this complex mix of technologies is listed below:. It is excellent for remote administration. It is also able to perform port redirection and tunneling so that ANY service or protocol can be inside the SSH encrypted connection, providing security to services that would otherwise be wide open to clear text information sniffing.
Fact or Fiction? By Jim Bird. New to SANS? Wondering what NetWars is? NetWars is a suite [ Perry II, University of Tennessee. I thoroughly recommend it. Best training ever! Toggle navigation. Malware FAQ. Malware FAQ: Hawke Robinson Overview Initially this document covers, from a high level, various popular VPN technologies and implementations.
This document then proceeds to delve into considerable depth about: The implementation. Lists several vulnerabilities in detail. Demonstrates in detail 5 attacks on various versions of the most common of Microsoft's PPTP products, using free, readily available tools Explains what each exploit is doing and how it works. The basics of Virtual Private Networks A Virtual Private Network, abbreviated as VPN, in it's most basic terms, is the use of various technologies to provide a private network of resources and information over any public network, including the Internet.
The VPN protocols mentioned include: Easy to setup and administrate, very low cost. Little to no protection, very vulnerable to many attacks, information "leakage" and more. Topology 2 VPN server behind a firewall but listening service ports still directly accessible for the ports that are allowed to be open by the firewall This is another common setup.
Easy setup and administration, and low cost Disadvantages: Still quite open and vulnerable to wide array of attacks. Topology 3 VPN Server behind a firewall and only accessible to certain ports via port forwarding from the firewall. Improved security "stance" still fairly easy to setup and administrate. Not quite as simple to setup as first two options, still not as many layers for a "security in depth" approach as there could be.
Much more secure stance, security in layers.
High complexity to setup and administrate, added cost, more advanced skill sets required. Slightly easier setup and administration than option 4. Security level is only about equivalent to option 3. Topology 6 Wireless such as the popular More secure wireless setup, fairly easy to setup and administrate Disadvantages: Every attack described in this document is very effective on such a network. Even if the attacker can't gain VPN access into the LAN, they can still possibly easily abuse the bandwidth on the wireless segment, and easily attack the server and users on this segment.
Targeted Service: Overview of Protocol: The GRE header also contains: Acknowledgment information Sequencing information The Control Connection TCP port actually determines the data rate and traffic congestion actions based on information from the GRE headers. Each PPTP Control Connection message starts with an 8 octet fixed header with the following information contained within: Microsoft's implementation of PPTP includes the following technologies: Convert the user's password to 14 byte string Truncate longer passwords or pad shorter passwords with nulls Convert all characters to uppercase Divide this 14 character string in half to create two 7 character strings Use each 7 character string as a DES key Encrypt a fixed constant with each key no random salt provided, entropy is based on the password This creates two 8 byte encrypted strings These two 8 byte strings are merged concatenated together to form a single 16 byte hashed string.
Topology 1
Compare this to when using the Windows NT hash: The password is by default a maximum of 14 characters, though it is easy enough to change this default to allow up to characters for the password, unfortunately most administrators do not do so. Password is case sensitive and converted to Unicode Password hashed using MD4 Produces a 16 byte hash There are many well-known and well-documented weaknesses in version 1 of Microsoft's implementation of PPTP. Discover the length of the key trivial since this is well published information Shift the ciphertext encrypted information by that length and XOR it with itself.
This will remove the key and reveal the plain text information. No true randomization "salt" to make the keys more unique Key length is dependent upon password length Entropy is based on password MS-CHAP v1 uses the following procedure for authentication: The 3 DES keys are used to encrypt the challenge into three 8 byte encrypted strings The 3 strings are concatenated together into a 24 byte string This 24 byte string is sent as a challenge reply to the server The server uses it's hashed record of the user's password to decrypt these replies sent by the client If decryption matches, then success message sent back to client MS-CHAP version 1 using the LANMAN hash has the weaknesses as described earlier in this document and more specifically applied to PPTP has the additional risks: The LANMAN hash is easily vulnerable to fast dictionary attacks A change password request dialogue can be initiated by an attacker to the client There are a number of easily available tools such as L0phtcrack or Crack v5.
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Enable the server to only accept the NT password hash for authentication, and reject any client trying to use the LANMAN password hash for authentication Enable the NT client to not use the LANMAN password hash for authentication, but only if the client is configured for the supposed " bit" encryption. Compare the description of version one to version 2 as follows: Client requests login challenge from server same as v1 The server sends the client a 16 byte random challenge differs from v1 Client generates PAC Peer Authenticator Challenge as a random 16 byte number differs from v1 Client concatenates the PAC and the 16 byte response from the server's challenge, and the client's username.
Unfortunately the following well published weakness were not addressed: Notice how the following information and "information leakage" is easily gleaned from this most basic and brief session of captured information: The vulnerabilities are summarized as: DoS Denial of Service: Can cause system crash by attacking GRE protocol 47 listening port on server another variation. Information Compromise: Incidents Chart The following chart from www. Specific MS PPTP Exploits This section will cover in detail the lab configuration used for testing, the tools used, and the steps of the exploits, and their results.
Lab Setup Lab consisted of over 20 systems used to perform a wide range of tests on different levels of hardware, network topology and software combinations. Time Period Fully updated systems using "Windows Update" and downloaded "service packs" to make systems current by installing ALL relevant updates available between March 1st through June 30th Systems Used Operating systems tested included: Higher end systems: Tools used Anger.
DoS Denial of Service Wariants: Supposedly affects some hardware types and not others. Only supposed to work against NT systems below Service Pack 6. Operating System s: Causes denial of PPTP services to clients and causes system instability and crash to blue screen Description of Variants: Undetermined what the common variable in hardware that causes some systems to crash easier than others. Protocol Description: Summary of Lab Testing Verified that the attack worked, though not as quickly as some articles described.
Exploit 2 Details Name: System will quickly blue screen shortly after the attack begins, this usually only requires about 50 packets to crash the PPTP server. Description of any exploit Variants: How the Exploit Works By using ipsend to send a number of malformed GRE packets to the target system, the PPTP server is unable to properly handle these packets and causes the system to become unresponsive.
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Summary of lab testing: How to use the exploit: No useful information in the Event Logs. How to protect against it: Exploit 3 Details Name: PPTP attack 3 using apsend to send malformed packets to GRE protocol, causing system resources to become consumed and server unusable. All versions of NT, all service packs. Follow the assistant until it only shows information about how awesome your system is going to be. If you still have no idea what you want. You're done with this step now. Installation Preferences 9. If you have Windows installed on the side. Then add another partition.
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On your new system. This can result in a very ugly black screen with lots of percentage messages. No need to download the Cisco client. If you don't intend keeping this page. Windows will recheck it's partition as it has been altered.
Why should you do that now? Because you can ask us if you have any questions or special wishes. If you haven't chosen to install updates during installation. This will only happen once. Have a good night! Confirm that you don't want to use a CA certificate. Leave the other fields as they are. More Software This is not necessary in KDE.
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