With de spread of Hackers and Hackin’ incidents, de time has come, when not only system administrators of servers of big companies, but also people who connect to de Internet by dialin’ up into deir ISP, have to worry about securin’ deir system. It really does not make much difference wheder you have a static IP or a dynamic one, if your system is connected to de Internet, den dere is every chance of it bein’ attacked.
This manual is aimed at discussin’ methods of system security analysis and will shed light on as to how to secure your standalone (also a system connected to a LAN) system.
Open Ports: A Threat to Security?
In de Netstat Tutorial we had discussed how de netstat -a command showed de list of open ports on your system. Well, anyhow, before I move on, I would like to quickly recap de important part. So here goes, straight from de netstat tutorial:
Now, de ??a? option is used to display all open connections on de local machine. It also returns de remote system to which we are connected to, de port numbers of de remote system we are connected to (and de local machine) and also de type and state of connection we have with de remote system.
For Example,
C:windows>netstat -a
Active Connections
Proto Local Address Foreign Address State
TCP ankit:1031 dwarf.box.sk:ftp ESTABLISHED
TCP ankit:1036 dwarf.box.sk:ftp-data TIME_WAIT
TCP ankit:1043 banners.egroups.com:80 FIN_WAIT_2
TCP ankit:1045 mail2.mtnl.net.in:pop3 TIME_WAIT
TCP ankit:1052 zztop.boxnetwork.net:80 ESTABLISHED
TCP ankit:1053 mail2.mtnl.net.in:pop3 TIME_WAIT
UDP ankit:1025 *:*
UDP ankit:nbdatagram *:*
Now, let us take a sin’le line from de above output and see what it stands for:
Proto Local Address Foreign Address State
TCP ankit:1031 dwarf.box.sk:ftp ESTABLISHED
Now, de above can be arranged as below:
Protocol: TCP (This can be Transmission Control Protocol or TCP, User Datagram Protocol or UDP or sometimes even, IP or Internet Protocol.)
Local System Name: ankit (This is de name of de local system that you set durin’ de Windows setup.)
Local Port opened and bein’ used by this connection: 1031
Remote System: dwarf.box.sk (This is de non-numerical form of de system to which we are connected.)
Remote Port: ftp (This is de port number of de remote system dwarf.box.sk to which we are connected.)
State of Connection: ESTABLISHED
?Netstat? with de ??a? argument is normally used, to get a list of open ports on your own system i.e. on de local system. This can be particularly useful to check and see wheder your system has a Trojan installed or not. Yes, most good Antiviral software are able to detect de presence of Trojans, but, we are hackers, and need to software to tell us, wheder we are infected or not. Besides, it is more fun to do somethin’ manually than to simply click on de ?Scan? button and let some software do it.
The followin’ is a list of Trojans and de port numbers which dey use, if you Netstat yourself and find any of de followin’ open, den you can be pretty sure, that you are infected.
Port 12345(TCP) Netbus
Port 31337(UDP) Back Orifice
For complete list, refer to de Tutorial on Trojans at: hackin’truths.box.sk/trojans.txt
Now, de above tutorial resulted in a number of people raisin’ questions like: If de ‘netstat -a’ command shows open ports on my system, does this mean that anyone can connect to them? Or, How can I close dese open ports? How do I know if an open port is a threat to my system’s security of not? Well, de answer to all dese question would be clear, once you read de below paragraph:
Now, de thin’ to understand here is that, Port numbers are divided into three ranges:
The Well Known Ports are those from 0 through 1023. This range or ports is bound to de services runnin’ on them. By this what I mean is that each port usually has a specific service runnin’ on it. You see dere is an internationally accepted Port Numbers to Services rule, (refer RFC 1700 Here) which specifies as to on what port number a particular service runs. For Example, By Default or normally FTP runs on Port 21. So if you find that Port 21 is open on a particular system, den it usually means that that particular system uses de FTP Protocol to transfer files. However, please note that some smart system administrators delibrately i.e. to fool lamers run fake services on popular ports. For Example, a system might be runnin’ a fake FTP daemon on Port 21. Although you get de same interface like de FTP daemon banner, response numbers etc, however, it actually might be a software loggin’ your prescence and sometimes even tracin’ you!!!
The Registered Ports are those from 1024 through 49151. This range of port numbers is not bound to any specific service. Actually, Networkin’ utlites like your Browser, Email Client, FTP software opens a random port within this range and starts a communication with de remote server. A port number within this range is de reason why you are able to surf de net or check your email etc.
If you find that when you give de netstat -a command, den a number of ports within this range are open, den you should probably not worry. These ports are simply opened so that you can get your software applications to do what you want them to do. These ports are opened temporarily by various applications to perform tasks. They act as a buffer transferin’ packets (data) received to de application and vis-a-versa. Once you close de application, den you find that dese ports are closed automatically. For Example, when you type www.hotmail.com in your browser, den your browser randomly chooses a Registered Port and uses it as a buffer to communicate with de various remote servers involved.
The Dynamic and/or Private Ports are those from 49152 through 65535. This range is rarely used, and is mostly used by trojans, however some application do tend to use such high range port numbers. For Example,Sun starts deir RPC ports at 32768.
So this basically brin’s us to what to do if you find that Netstat gives you a couple of open ports on your system:
1. Check de Trojan Port List and check if de open port matches with any of de popular ones. If it does den get a trojan Removal and remove de trojan.
2. If it doesn’t or if de Trojan Remover says: No trojan found, den see if de open port lies in de registered Ports range. If yes, den you have nothin’ to worry, so forget about it.
HACKING TRUTH: A common technique employed by a number of system administrators, is remappin’ ports. For example, normally de default port for HTTP is 80. However, de system administrator could also remap it to Port 8080. Now, if that is de case, den de homepage hosted at that server would be at:
domain.com:8080 instead of
domain.com:80
The idea behind Port Remappin’ is that instead of runnin’ a service on a well known port, where it can easily be exploited, it would be better to run it on a not so well known port, as de hacker, would find it more difficult to find that service. He would have to port scan high range of numbers to discover port remappin’.
The ports used for remappin’ are usually pretty easy to remember. They are choosen keepin’ in mind de default port number at which de service bein’ remapped should be runnin’. For Example, POP by default runs on Port 110. However, if you were to remap it, you would choose any of de followin’: 1010, 11000, 1111 etc etc
Some sysadmins also like to choose Port numbers in de followin’ manner: 1234,2345,3456,4567 and so on… Yet anoder reason as to why Port Remappin’ is done, is that on a Unix System to be able to listen to a port under 1024, you must have root previledges.
Firewalls
Use of Firewalls is no longer confined to servers or websites or commerical companies. Even if you simply dial up into your ISP or use PPP (Point to Point Protocol) to surf de net, you simply cannot do without a firewall. So what exactly is a firewall?
Well, in non-geek lan’uage, a firewall is basically a shield which protects your system from de untrusted non-reliable systems connected to de Internet. It is a software which listens to all ports on your system for any attempts to open a connection and when it detects such an attempt, den it reacts accordin’ to de predefined set of rules. So basically, a firewall is somethin’ that protects de network(or systen) from de Internet. It is derived from de concept of firewalls used in vehicles which is a barrier made of fire resistant material protectin’ de vehicle in case of fire.
Now, for a better ‘accordin’ to de bible’ defination of a firewall: A firewall is best described as a software or hardware or both Hardware and Software packet filter that allows only selected packets to pass through from de Internet to your private internal network. A firewall is a system or a group of systems which guard a trusted network( The Internal Private Network from de untrusted network (The Internet.)
NOTE: This was a very brief desciption of what a firewall is, I would not be goin’ into de details of deir workin’ in this manual.
Anyway,de term ‘Firewalls’, (which were generally used by companies for commerical purposes) has evolved into a new term called ‘Personal Firewalls’. Now this term is basically used to refer to firewalls installed on a standalone system which may or may not be networked i.e. It usually connects to an ISP. Or in oder words a personal firewall is a firewall used for personal use.
Now that you have a basic desciption as to what a firewall is, let us move on to why exactly you need to install a Firewall? Or, how can not installin’ a firewall pose a threat to de security of your system?
You see, when you are connected to de Internet, den you have millions of oder untrusted systems connected to it as well. If somehow someone found out your IP address, den dey could do probably anythin’ to your system. They could exploit any vulnerability existin’ in your system, damage your data, and even use your system to hack into oder computers.
Findin’ out someone’e IP Address is not very difficult. Anybody can find out your IP, through various Chat Services, Instant Messengers (ICQ, MSN, AOL etc), through a common ISP and numerous oder ways. Infact findin’ out de IP Address of a specific person is not always de priority of some hackers.
What I mean to say by that is that dere are a number of Scripts and utilities available which scan all IP addresses between a certain range for predefined common vulnerabilities. For Example, Systems with File Sharin’ Enabled or a system runnin’ an OS which is vulnerable to de Pin’ of Death attack etc etc As soon as a vulnerable system is found, den dey use de IP to carry out de attacks.
The most common scanners look for systems with RAT’s or Remote Administration Tools installed. They send a packet to common Trojan ports and display wheder de victim’s system has that Trojan installed or not. The ‘Scan Range of IP Addresses’ that dese programs accept are quite wide and one can easily find a vulnerable system in de matter of minutes or even seconds.
Trojan Horses like Back Orifice provide remote access to your system and can set up a password sniffer. The combination of a back door and a sniffer is a dangerous one: The back door provides future remote access, while de sniffer may reveal important information about you like your oder Passwords, Bank Details, Credit Card Numbers, Social Security Number etc If your home system is connected to a local LAN and de attacker manages to install a backdoor on it, den you probably have given de attacker de same access level to your internal network, as you have. This wouls also mean that you will have created a back door into your network that bypasses any firewall that may be guardin’ de front door.
You may argue with me that as you are usin’ a dial up link to your ISP via PPP, de attacker would be able to access your machine only when you are online. Well, yes that is true, however, not completely true. Yes, it does make access to your system when you reconnect, difficult, as you have a dynamic Internet Protocol Address. But, although this provides a faint hope of protection, routine scannin’ of de range of IP’s in which your IP lies, will more often than not reveal your current Dynamic IP and de back door will provide access to your system.
HACKING TRUTH: Microsoft Says: War Dialer programs automatically scan for mothems by tryin’ every phone number within an exchange. If de mothem can only be used for dial-out connections, a War Dialer won’t discover it. However, PPP changes de equation, as it provides bidirectional transportmakin’ any connected system visible to scanners?and attackers.
So how do I protect myself from such Scans and unsolicitated attacks? Well, this is where Personal Firewalls come in. They just like deir name suggests, protect you from unsolicitated connection probes, scans, attacks.
They listen to all ports for any connection requests received (from both legitimate and fake hosts) and sent (by applications like Browser, Email Client etc.) As soon as such an instance is recorded, it pops up a warnin’ askin’ you what to do or wheder to allow de connection to initiate or not. This warnin’ message also contains de IP which is tryin’ to initiate de connection and also de Port Number to which it is tryin’ to connect i.e. de Port to which de packet was sent. It also protects your system from Port Scans, DOS Attacks, Vulnerability attacks etc. So basically it acts as a shield or a buffer which does not allow your system to communicate with de untrusted systems directly.
Most Personal Firewalls have extensive loggin’ facilities which allows you to track down de attackers. Some popular firewalls are:
1.BlackICE Defender : An IDS for PC’s. It’s available at www.networkice.com.
2. ZoneAlarm: The easiest to setup and manage firewall. Get it for free at: www.zonelabs.com
Once you have installed a firewall on your system, you will often get a number of Warnin’s which might seem to be as if someone is tryin’ to break into your system, however, dey are actually bogus messages, which are caused by eider your OS itself or due to de process called Allocation of Dynamic IP’s. For a details description of dese two, read on.
Many people complain that as soon as dey dial into deir ISP, deir firewall says that such and such IP is probin’ Port X. What causes them?
Well, this is quite common. The cause is that somebody hun’ up just before you dialed in and your ISP assigned you de same IP address. You are now seein’ de remains of communication with de previous person. This is most common when de person to which de IP was assigned earlier was usin’ ICQ or chat programs, was connected to a Game Server or simply turned off his mothem before his communication with remote servers was complete.
You might even get a message like: Such and Such IP is tryin’ to initaite a Netbios Session on Port X. This again is extrememly common. The followin’ is an explanation as to why it happens, which I picked up a couple of days ago: NetBIOS requests to UDP port 137 are de most common item you will see in your firewall reject logs. This comes about from a feature in Microsoft’s Windows: when a program resolves an IP address into a name, it may send a NetBIOS query to IP address. This is part of de background radiation of de Internet, and is nothin’ to be concerned about.
What Causes them? On virtually all systems (UNIX, Macintosh, Windows), programs call de function ‘gethostbyaddr()’ with de desired address. This function will den do de appropriate lookup, and return de name. This function is part of de sockets API. The key thin’ to remember about gethostbyaddr() is that it is virtual. It doesn’t specify how it resolves an address into a name. In practice, it will use all available mechanisms. If we look at UNIX, Windows, and Macintosh systems, we see de followin’ techniques:
DNS in-addr.arpa PTR queries sent to de DNS server
NetBIOS NodeStatus queries sent to de IP address
lookups in de /etc/hosts file
AppleTalk over IP name query sent to de IP address
RPC query sent to de UNIX NIS server
NetBIOS lookup sent to de WINS server
Windows systems do de /etc/hosts, DNS, WINS, and NodeStatus techniques. In more excruciatin’ detail, Microsoft has a generic system component called a namin’ service. All de protocol stacks in de system (NetBIOS, TCP/IP, Novel IPX, AppleTalk, Banyan, etc.) register de kinds of name resolutions dey can perform. Some RPC products will likewise register an NIS namin’ service. When a program requests to resolve an address, this address gets passed onto de generic namin’ service. Windows will try each registered name resolution subsystem sequentially until it gets an answer.
(Side note: User’s sometimes complained that accessin’ Windows servers is slow. This is caused by installin’ unneeded protocol stacks that must timeout first before de real protocol stack is queried for de server name.).
The order in which it performs dese resolution steps for IP addresses can be configured under de Windows registry key
HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesTcpipServiceProvider.
Breakin’ Through Firewalls
Although Firewalls are meant to provide your complete protection from Port Scan probes etc dere are several holes existin’ in popular firewalls, waitin’ to be exploited. In this issue, I will discuss a hole in ZoneAlarm Version 2.1.10 to 2.0.26, which allows de attacker to port scan de target system (Although normally it should stop such scans.)
If one uses port 67 as de source port of a TCP or UDP scan, ZoneAlarm will let de packet through and will not notify de user. This means, that one can TCP or UDP port scan a ZoneAlarm protected computer as if dere were no firewall dere IF one uses port 67 as de source port on de packets.
Exploit:
UDP Scan:
You can use NMap to port scan de host with de followin’ command line:
nmap -g67 -P0 -p130-140 -sU 192.168.128.88
(Notice de -g67 which specifies source port).
TCP Scan:
You can use NMap to port scan de host with de followin’ command line:
nmap -g67 -P0 -p130-140 -sS 192.168.128.88
(Notice de -g67 which specifies source port).
