Firewall Forensics - What Am I Seeing?

This document is intended for both security-experts maintaining corporate firewalls as well as home users of personal firewalls.

0. Information about this FAQ

Version 1.2.0, January, 2003
http://www.robertgraham.com/pubs/firewall-seen.html
 

Copyright 1998-2003 by Robert Graham (mailto:firewall-seen1@robertgraham.com.
All rights reserved. Note that I care that people properly attribute this work but I don't care much of others profit by copying it.

Special thanks to Alan J. Rosenthal (maintainer of FAQs himself) for some really good input.

 

TOC

1. What does destination port number ZZZZ mean?

PORT GUIDE  | source-ports | many-to-one | trojans | DNS | dial-up | IRC | remapping | still can't figure it out

2. What does this ICMP info mean?

0 (echo reply) | 3 (unreachable) | 4 (source quench) | 8 (ping) | 11 (ttl exceeded) 12 (problem)

3. What do these IP addresses indicate?

source-routing | 255.255.255.255 | track owner | 10.x.x.x | known IP addresses | 0.0.0.0 | directed-broadcasts | 169.254.x.x

4. Stuff doesn't work

slow connections

5. What are some typical signatures of well-known programs?

traceroute | sscan | proxy scanners | smurf | fraggle

7. What do these other logs mean?

DNS | HTTP | RPC | SMTP | identd

8. How do I configure filters?

ICMP filters | split DNS

9. Packet Zen

IP ID | TTL | Resources

10. What's the deal with NetBIOS (UDP port 137)?

What? | Why? | But I'm not Win? | Statistics | Signature | Get rid of them? | Attacks

A. Appendix

You'll note that some sections are missing. This is an evolving document; when sections are removed (because the info is moved into other sections), I don't renumber the document.

 

1. What does destination port number ZZZZ mean?

All the traffic going through the firewall is part of a connection. A connection consists of the pair of IP addresses that are talking to each other, as well a pair of port numbers that identify the protocol or service. The destination port number of the first packet often indicates the type of service being connected to. When a firewall blocks a connection, it will save the destination port number to its logfile. This section describes some of the meanings of these port numbers.

Port numbers are divided into three ranges:

• The Well Known Ports are those from 0 through 1023. These are tightly bound to services, and usually traffic on this port clearly indicates the protocol for that service. For example, port 80 virtually always indicates HTTP traffic.
• The Registered Ports are those from 1024 through 49151. These are loosely bound to services, which means that while there are numerous services "bound" to these ports, these ports are likewise used for many other purposes that have nothing to do with the official server.
• The Dynamic and/or Private Ports are those from 49152 through 65535. In theory, no service should be assigned to these ports.

In reality, machines start assigning "dynamic" ports starting at 1024. We also see strangeness, such as Sun starting their RPC ports at 32768.

Where to get a more complete list of port info:

http://www.isi.edu/in-notes/iana/assignments/port-numbers

"Assigned Numbers" RFC, the official source for port assignments.

http://advice.networkice.com/advice/Exploits/Ports/

Database of port numbers, hyper-linked to various exploits on those port numbers.

/etc/services

On UNIX systems, the file /etc/services contains a list of commonly used UNIX port number assignments. On Windows NT, this file is located in %systemroot%/system32/drivers/etc/services.

http://www.con.wesleyan.edu/~triemer/network/docservs.html

Links back to the protocol specifications frequently.

http://www.chebucto.ns.ca/~rakerman/trojan-port-table.html

Frequently updated page by Richard Akerman with good/solid info.

http://www.tlsecurity.com/trojanh.htm

TLSecurity's list of Trojans. Rather than a collection of rumors by other people, the maintainers of this list claim to verify each and every port personally.

http://www.simovits.com/nyheter9902.html

Trojan Horse probes page.

 

1.1 What are some common incoming TCP/UDP probes against my firewall?

This section contains a list of common TCP and UDP port scans that people see against their firewalls. (Look in section 2 for ICMP info).

0		Commonly used to help determine the operating system. This works because on some systems, port 0 is "invalid" and will generate a different response when you connect to it vs. a normal closed port. One typical scan uses a destination IP address of 0.0.0.0 and sets the ACK bit, with broadcast at the Ethernet layer.
1	tcpmux	Indicates someone searching for SGI Irix machines. Irix is the only major vendor that has implemented tcpmux, and it is enabled by default on Irix machines. Irix machines ship with several default passwordless accounts, such as lp, guest, uucp, nuucp, demos, tutor, diag, EZsetup, OutOfBox, and 4Dgifts. Many administrators forget to close these accounts after installation. Therefore, hackers scan the Internet looking first for tcpmux, then these accounts. [ CA-1995-15 RFC 1078 ]
7	Echo	You will see lots of these from people looking for fraggle amplifiers sent to addresses of x.x.x.0 and x.x.x.255. A common DoS attack is an echo-loop, where the attacker forges a UDP from one machine and sends it to the other, then both machines bounce packets off each other as fast as they can (see also chargen). [CA-96.01] Another common thing seen is TCP connections to this port by DoubleClick. They use a product called "Resonate Global Dispatch" that connects to this port on DNS servers in order to locate the closest one. Harvest/squid caches will send tbese UDP echoes from port 3130. To quote their document: If the cache is configured with source_ping on, it also bounces a HIT reply off the original host's UDP echo port. It can generate a lot of these packets.
11	sysstat	This is a UNIX service that will list all the running processes on a machine and who started them. This gives an intruder a huge amount of information that might be used to compromise the machine, such as indicating programs with known vulnerabilities or user accounts. It is similar the contents that can be displayed with the UNIX "ps" command. This service is usually disabled, scans for this don't expect to actually succeed most of the time. Some people come here looking for ICMP port 11. To repeat: firewall logs are confusing, ICMP doesn't have ports; if you see something that says "ICMP port 11", you probably want ICMP type=11.
19	chargen	This is a service that simply spits out characters for testing purposes. The UDP version will respond with a packet containing garbage characters whenever a UDP packet is received. On a TCP connection, it spits out a stream of garbage characters until the connection is closed. Hackers can take advantage of IP spoofing for denial of service attacks. Forging UDP packets between two chargen servers, or a chargen and echo can overload links as the two servers attempt to infinitely bounce the traffic back and forth. Likewise, the "fraggle" DoS attack broadcasts a packet destined to this port with a forged victim address, and the victim gets overloaded with all the responses. [CA-96.01]
21	FTP	The most common attack you will see are hackers/crackers looking for "open anonymous" FTP servers. These are servers with directories that can be written to and read from. Hackers/crackers use these machines as way-points for transferring warez (pirated programs) and pr0n (intentionally misspelled word to avoid search engines classifying this document). In early 2003, I occasionally see people trying to exploit the FTP server using a wide sprectrum of vulnerabilities. For example, I see them try several kinds of buffer-overflows.
22	ssh pcAnywhere	SSH is a popular way to remotely run a command-prompt on systems, primarily UNIX systems. It provides secure authentication and encryption, so it is especially popular among security professionals. There is a commercial version by the company that originally created it, a popular open-source OpenSSH alternative, and many other compatible versions. In 2002, numerous vulnerabilities in most all versions were discovered, exploited, and routinely scanned for. Many security professionals had their boxes compromised through SSH -- in many cases, SSH was the only service they had remotely reachable. Also note that the ssh package comes with a program called make-ssh-known-hosts that will scan a domain for ssh hosts. You will sometimes be scanned from innocent people running this utility. UDP (rather than TCP) packets directed at this port along with port 5632 indicate a scan for pcAnywhere. The number 5632 is (hex) 0x1600, which byte-swapped is 0x0016, which is 22 decimal. [CA-2002-36] [CA-2002-18] [CA-2001-35] [CA-1999-15]
23	Telnet	Telnet is the most popular protocol for getting a remote command line. The most common use by scanners is to get the "banner" that prompts the user for a login name. The banner tells a lot about system -- often the attacker isn't interested in actually exploiting Telnet as to figure out more about the system when attacking other ports. As of 2002, most attackers are interested in finding network equipment such as switches and routers, especially Cisco equipment. When my honeypot gives them a command prompt, they spend more time trying out Cisco commands than they do things like "uname" to figure out what system they are running on. Historically (and still common as of 2002), hackers look for Unix systems with default accounts. They will try a series of logon names and empty passwords. Since Unix systems have largely fixed this problem of default accounts, this has become a less popular attack.
25	SMTP	SMTP (Simple Mail Transfer Protocol) is the protocol that transfers virtuall all the world's e-mail. Scans against this port are almost certain coming from spammers (and occasionally anti-spammers) looking for "open relays". An open relay is a mail server that will accept e-mail from anyone and forward it on. This allows the spammer to hide behind the relay, as well as take advantage of the fact that they can submit one e-mail with 20 recipients -- and the relay will do the job of sending copies to each recipient. This lowers the spammer's bandwidth costs. Note that there continue to be vulnerabilities in mail servers themselves.
53	DNS	DNS (Domain Name Service) is a core Internet protocol; it translates names into Internet addresses (like a phonebook translates names into phone numbers). It is so important that when DNS servers go down, users usually think the Internet itself has gone down. Ways of breaking into DNS servers are frequently discovered, such as the BIND exploit in 2002. The BIND (Berkeley Internet Name Daemon) is the most popular DNS server. Many UDP packets you see rejected by the firewall are looking for the name "version.bind", which will tell the hacker what version of BIND you are (hopefully) running, and therefore which exploits they can run to break into your service. If you put a vulnerable version of BIND on the Internet, it will likely be compromised in a few days. DNS information tells the hacker a lot of about the intended victim. Rejected TCP attempts probably reflect a desire by the hacker to do a "zone transfer", which will list all the computers in your domain. Victims often name systems in ways that help hackers figure out what is going on, such as "cisco-rtr.example.com" or "payroll.example.com". Since DNS is such an important protocol to the Internet, firewall administrators often allow port 53 when they shouldn't. They sacrifice security in order to get ease-of-use and reliability. This allows hackers to use port 53 for protocols other than DNS. An important thing to note is that you will frequently see port 53 used as the source UDP port. Stateless firewalls frequently allow such traffic on the assumption that it is a response to a DNS query. Hackers are increasingly exploiting this to pierce firewalls.
67 and 68	bootp DHCP	DHCP (and the older version, BOOTP) are the protocols that assign your desktop computer an IP address. Firewalls will see (and reject) a lot of DHCP requests from your local network. This is an interesting problem with cable and DSL modems, because they create "virtual" local networks including people in your nearby physical neighborhood. You can identify these local requests because they are not sent to you, but are are instead to what's called the "local broadcast" address: 255.255.255.255. These machines are asking to for an address assignment from a DHCP server. You could probably hack into them by giving them such an assignment and specifying yourself as the local router, then execute a wide range of man-in-the-middle attacks. The client requests configuration on a broadcast to port 68 (bootps). The server broadcasts back the response to port 67 (bootpc). The response uses some type of broadcast because the client doesn't yet have an IP address that can be sent to. You rarely see attackers from remote parts of the Internet trying to exploit DHCP vulnerabilities. As of 2003, an important exploit has been found in a DHCP service, so remote hackers may start scanning for this. [CA-2003-01]
69	TFTP	(over UDP). Many servers support this protocol in conjunction with BOOTP in order to download boot code to the system. However, they are frequently misconfigured to provide any file from the system, such as password files. They can also be used to write files to the system.
79	finger	Hackers are trying to: discover user information fingerprint the operating system exploit known buffer-overflow bugs bounce finger scans through your machine to other machines.
80	http	Prior to 2003, I did not include an entry for this port. Presumably, you would know what port 80 meant without this guide having to tell you. However, a enormous number of worms infecting Windows and Unix systems are now using this port, so I am including it for worm discussion.
98	linuxconf	The utility "linuxconf" provide easy administration of Linux boxen. It includes a web-enabled interface at port 98 through an integrated HTTP server. It has had a number of security issues. Some versions are setuid root, trust the local network, create world-accessible files in /tmp, and a buffer overflow in the LANG environment variable. Also, because it contains an integrated web server, it may be vulnerable to many of the typical HTTP exploits (buffer overruns, directory traversal using ../.., etc.).
109	POP2	POP2 is not nearly as popular as POP3 (see below), but many servers support both (for backwards compatibility). Many of the holes that can be exploited on POP3 can also be exploited via the POP2 port on the same server.
110	POP3	POP3 is used by clients accessing e-mail on their servers. POP3 services have many well-known vulnerabilities. At least 20 implementations are vulnerable to a buffer overflow in the username or password exchange (meaning that hackers can break in at this stage before really logging in). There are other buffer overflows that can be executed after successfully logging in.
111	sunrpc portmap rpcbind	Sun RPC PortMapper/RPCBIND. Access to portmapper is the first step in scanning a system looking for all the RPC services enabled, such as rpc.mountd, NFS, rpc.statd, rpc.csmd, rpc.ttybd, amd, etc. If the intruder finds the appropriate service enabled, s/he will then run an exploit against the port where the service is running. Note that by putting a logging daemon, IDS, or sniffer on the wire, you can find out what programs the intruder is attempting to access in order to figure out exactly what is going on.
113	identd auth	This is a protocol that runs on many machines that identifies the user of a TCP connection. In standard usage this reveals a LOT of information about a machine that hackers can exploit. However, it used by a lot of services by loggers, especially FTP, POP, IMAP, SMTP, and IRC servers. In general, if you have any clients accessing these services through a firewall, you will see incoming connection attempts on this port. Note that if you block this port, clients will perceive slow connections to e-mail servers on the other side of the firewall. Many firewalls support sending back a RST on the TCP connection as part of the blocking procedure, which will stop these slow connections.
119	NNTP news	Network News Transfer Protocol, carries USENET traffic. This is the port used when you have a URL like news://comp.security.firewalls/. Attempts on this port are usually by people hunting for open USENET servers. Most ISPs restrict access to their news servers to only their customers. Open news servers allow posting and reading from anybody, and are used to access newsgroups blocked by someone's ISP, to post anonymously, or to post spam. Update: @Home has started scanning their subscribers to see if they are running USENET servers. They are doing this in order to find these servers and close them before spammers can take advantage of them.
135	loc-serv MS RPC end-point mapper	As of 2003, the most common reason you see port 135/udp is because of WinPopup/Messenger spam. This is a feature in Windows that allows system administrators to notify employees of unusual events, such as the network or file servers about to be rebooted. However, spammers have found a way to subvert this and use this mechanism to send popup messages on the victim's desktop. Microsoft runs its DCE RPC end-point mapper for its DCOM services at this port. This has much the same functionality as port 111 for UNIX systems. Services that use DCOM and/or RPC register their location with the end-point mapper on the machine. When clients remotely connect to the machine, they query the end-point mapper to find out where the service is. Likewise, hackers can scan the machine on this port in order to find out such things as "is Exchange Server running on this machine, and which version?". This port is often hit in order to scan for services (for example, using the "epdump" utility), but this port may also be attacked directly. Currently, there are a few denial-of-service attacks that can be directed at this port. No RPC service except the endpoint mapper runs on this port, except that "broadcast" messages intended for other RPC services can be forwarded through this port.
137	NetBIOS name service nbtstat	(UDP) This is the most common item seen by firewall administrators and is perfectly normal. Please read the NetBIOS section below for more details.
139	NetBIOS File and Print Sharing	Incoming connections to this port are trying to reach NetBIOS/SMB, the protocols used for Windows "File and Print Sharing" as well as SAMBA. People sharing their hard disks on this port are probably the most common vulnerability on the Internet. 2000 Attempts on this port were common at the beginning of 1999, but tapered off near the end. Now at the start of year 2000, attempts on this port have picked up again. Several VBS (IE5 VisualBasic Scripting) worms have appeared that attempt to copy themselves on this port. Therefore, it may be worms attempting to propagate on this port. 2001 In late 2001 and early 2002, the Nimda worm would share the C$ drive when it infected a machine. Many attempts against this port are from people scanning for drives left open by Nimda. 2002 In late 2002, the ALEVIR worm is propagating heavily throughout the Internet infecting Win95/Win98/WinMe machines. These have a bug that allows a hacker to connect to a password-protected share by using only the first character of a password, which is easy to guess. Most connection attempts to port 139 are from this worm. future WinXP is moving away from using port 139, more and more ISPs are blocking it.
143	IMAP4	Same security idea as POP3 above, numerous IMAP servers have buffer overflows that allow compromise during the login. Note that for awhile, there was a Linux worm (admw0rm) that would spread by compromising port 143, so a lot of scans on this port are actually from innocent people who have already been compromised. IMAP exploits became popular when RedHat enabled the service by default on its distributions. In fact, this may have been the first widely scanned for exploit since the Morris Worm. This port is also used for IMAP2, but that version wasn't very popular. Several people have noted attacks from port 0 to port 143, which appears to be from some attack script.
161	SNMP	(UDP) A very common port that intruders probe for. SNMP allows for remote management of devices. All the configuration and performance information is stored in a database that can be retrieved or set via SNMP. Many managers mistakeningly leave this available on the Internet. Crackers will first attempt to use the default passwords "public" and "private" to access the system; they may then attempt to "crack" the password by trying all combinations. SNMP packets may be mistakenly directed at your network. Windows machines running HP JetDirect remote management software uses SNMP, and misconfigured machines are frequent. HP OBJECT IDENTIFIERs will be seen in the packets. Newer versions of Win98 will use SNMP for name resolution; you will see packets broadcast on local subnets (cable modem, DSL) looking up sysName and other info. In early 2002, a university in Finland released its "PROTOS" tool that demonstrated many flaws in popular SNMP implementations. These flaws had been known for more than a decade, but this was the first time security implications were shown for these flaws.
162	SNMP trap	Probably a misconfiguration.
177	xdmcp	Numerous hacks may allow access to an X-Window console; it needs port 6000 open as well in order to really succeed.
445	NetBIOS File and Print Sharing	See port 139 for more information. In Windows 2000 and Windows XP, port 445 is essentially a duplicate of port 139. These ports are used for Micrsoft's file and printer sharing, remote registry access, named pipes services, and many MS-RPC services. The difference is that port 139 supports these services on top of NetBIOS, whereas port 445 gets rid of this middleman, supporting these services directly over TCP/IP. Whereas many ISPs now filter port 139, many do not filter port 445. As of mid-2002, we are seeing more scans for port 445 as hackers learn to get around port 139 filters. In late 2002, we are seeing worms propogate via this port.
513	rwho	Probably from UNIX machines on your DSL/cable-modem segment broadcasting who is logged into their servers. These people are kindly giving you really interesting information that you can use to hack into their systems.
515	lp printer	This is the standard protocol for remote printing on UNIX systems. Virtually every UNIX system from Sun Solaris to Linux will listen on this port. In addition, most laster printers support this protocol as well. There are widespread vulnerabilities on this port, due either to vulnerabilities in the protocol itself, or vulnerabilities in printer-specific drivers behind this port. The RedHat 7 LPRng bug was exploited by the Ramen worm in early 2001. As of late 2002, this is one of the more common ports probed, both because of Linux worms propogating, but also from hackers looking for well-know vulnerabilities.
535	CORBA IIOP	(UDP) If you are on a cable-modem or DSL VLAN, then you may see broadcasts to this port. CORBA is an object-oriented remote procedure call (RPC) system. It is highly likely that when you see these broadcasts, you can use the information to hack back into the systems generating these broadcasts. There are many exploits possible against this port, but as of August 2002, they haven't been reported to Bugtraq yet.
600	pcserver backdoor	See port 1524 for more info. Some script kiddies feel they're contributing substantially to the exploit programs by making a minor change from ingreslock to pcserver in constant text... -- Alan J. Rosenthal.
635	mountd	Linux mountd bug. This is a popular bug that people are scanning for. Most scans on this port are UDP-based, but they are increasingly TCP-based (mountd runs on both ports simultaneously). Note that mountd can run at any port (for which you must first do a portmap lookup at port 111), it's just that Linux defaulted to port 635 in much the same way that NFS universally runs at port 2049.
1024	-----	Many people ask the question what this port is used for. The answer is that this is the first port number in the dynamic range of ports. Many applications don't care what port they use for a network connection, so they ask the operating system to assign the "next freely available port". In point of fact, they as for port 0, but are assigned one starting with port 1024. This means the first application on your system that requests a dynamic port will be assigned port 1024. You can test this fact by booting your computer, then in one window open a Telnet session, and in another window run "netstat -a". You will see that the Telnet application has been assigned port 1024 for its end of the connection. As more applications request more and more dynamic ports, the operating system will assign increasingly higher port numbers. Again, you can watch this effect with 'netstat' as your browse the Internet with your web browser, as each web-page requires a new connection.
1025	-----	See port 1024.
1026	-----	See port 1024.
1027	-----	See port 1024.
1080	SOCKS	This protocol tunnels traffic through firewalls, allowing many people behind the firewall access to the Internet through a single IP address. In theory, it should only tunnel inside traffic out towards the Internet. However, it is frequently misconfigured and allows hackers/crackers to tunnel their attacks inwards, or simply bounce through the system to other Internet machines, masking their attacks as if they were coming from you. WinGate, a popular Windows personal firewall, is frequently misconfigured this way. In the year 2000, much activity on this port was for the purpose of connecting to IRC chatrooms. Usually the goal was DoS the chatroom. For this reason, most IRC servers will not scan your machine for SOCKS out of self-defense: they want to make sure that you are a legitimate user and now somebody who left the SOCKS service running that a hacker is tunneling through. In the year 2003, most of this activity is now by spammers. They are looking for SOCKS servers in order to funnel spam through. This hides the original source of the spam. There are several websites that maintain lists of open SOCKS servers. In 2002, most of the scans I see were from people who maintain these lists.
1114	SQL	This is rarely probed by itself, but is almost always seen as part of the sscan script.
1243	Sub-7	Trojan Horse (TCP). See the section on SubSeven for more details.
1433	MS SQL	Microsoft runs its SQL database server on this port. In the year 2002, several worms started exploiting this port. See section 11.2 for more information.
1434	MS SQL Service Discovery Protocol worm	Microsoft's SQL server uses this port for discovery of SQL services on the local LAN. On January 26, 2003, the SQLslammer worm took down parts of the Internet in the early hours of the morning. It took advantage of a buffer overflow on this service. Administrators quickly respond by widely configuring packet filters throughout the Internet, so by the time many people woke up in the morning in the U.S., much of the problem had gone away. See section 11.3 for more info.
1524	ingreslock backdoor	Many attack scripts install a backdoor shell at this port (especially those against Sun systems via holes in sendmail and RPC services like statd, ttdbserver, and cmsd). If you've just installed your firewall and are seeing connection attempts on this port, then this may be the cause. Try telnetting to the attempted machine in order to see if it indeed comes up with a shell. Connections to port 600/pcserver also have this problem. [IN-99-04]
2049	NFS	The NFS program usually runs at this port. Normally, access to portmapper is needed to find which port this service runs on, but since most installations run NFS on this port, hackers/crackers can bypass portmapper and try this port directly.
2766	listen npls	Used by Sun Solaris boxes as a printer service, alternative to the standard printer on port 515. Exploit scripts against Solaris machines will frequently bind a shell to this port, similar to the ingreslock port. In particular, a well-known exploit against the snmpXdmid vulnerability left behind a shell on this port.
3128	squid	This is the default port for the "squid" HTTP proxy. An attacker scanning for this port is likely searching for a proxy server they can use to surf the Internet anonymously. You may see scans for other proxies at the same time, such as at port 8000/8001/8080/8888. Another cause of scans at this port, for a similar reason, is when users enter chatrooms. Others users (or the servers themselves) will attempt to check this port to see if the user's machines supports proxying. See section 5.3 for more info.
5632	pcAnywhere	You may see lots of these, depending on the sort of segment you are on. When a user opens pcAnywhere, it scans the local Class C range looking for potential agents. Hackers/crackers also scan looking for open machines, so look at the source address to see which it is. Some scans for pcAnywhere frequently also include a UDP packet to port 22. See dialup probes for more info.
6776	Sub7 artifact	This port is used separately from the SubSeven main port to transfer data. One example where you might see this is when a master is controling a slave on a dialup line, then the slave machine hangs up. Therefore, when someone else dials-in at that IP address, they will see a continuous stream of connection attempts at this port. more on dialups
6970	RealAudio	Clients receive incoming audio streams from servers on UDP ports in the range 6970-7170. This is setup by the outgoing control connection on TCP port 7070.
13223	PowWow	The "PowWow" chat program from Tribal Voice. It allows users to open up private chat connections with each other on this port. The program is very aggressive at trying to establish the connection and will "camp" on the TCP port waiting for a response. This causes a connection attempt at regular intervals like a heartbeat. This can be seen by dial-up users who inherit IP addresses from somebody who was chatting with other people: it will appear as if many different people are probing that port. The protocol uses the letters "OPNG" as the first four bytes of its connection attempt. more
17027	Conducent	Outbound: This is seen on outbound connections. It is caused by users inside the corporation who have installed shareware programs using the Conducent "adbot" wrapper. This wrapper shows advertisements to users of the shareware. A popular shareware program that uses this is PKware. Bill Royds mentions that in his experience, you can block this outbound connection with no problem, but if you block the IP addresses themselves, then the adbots can overload the link trying to reach the servers by continually connecting many times per second. The machines will attempt to resolve the DNS name "ads.conducent.com", which resolve to the IP addresses: 216.33.210.40 216.33.199.77 216.33.199.80 216.33.199.81 216.33.210.41 These addresses are hosted by Exodus.
27374	Sub-7	Trojan Horse (TCP). See the section on SubSeven for more details. Also used as a backdoor port left behind by exploit scripts, such as those in the Ramen worm. While some scans for this port may be due to SubSeven, others may be looking for a remote shell.
30100	NetSphere	Trojan Horse (TCP). This is a commonly seen scan looking for systems compromised by this trojan.
31337	Back Orifice "elite"	This number means "elite" in hacker/cracker spelling (3=E, 1=L, 7=T). Lots of hacker/cracker backdoors run at this port, but the most important is Back Orifice. At one time, this was by far the most popular scan on the Internet. These days, it's popularity is waning and other remote access trojans are becoming popular.
31789	Hack-a-tack	UDP traffic on this port is currently being seen due to the "Hack-a-tack" RAT (Remote Access Trojan). This trojan includes a built-in scanner that scans from port 31790, so any packets FROM 31789 TO 317890 indicate a possible intrusion. (Port 31789 is the control connection; port 31790 is the file transfer connection).
32770 ~ 32900	RPC services	Sun Solaris puts most of its RPC services in this range. In particular, older versions of Solaris (pre-2.5.1) put a portmapper in this range, allowing hackers access to this even when low ports are blocked by a firewall. Probes in this range might either be for this portmapper, or for known RPC services that can be exploited.
33434 - 33600	traceroute	If you see a series of UDP packets within this port range (and only within thisrange), then it is probably indicative of traceroute. See traceroute for more info.
41508	Inoculan	Inoculan on UDP. Older versions of Inoculan apparently generate huge quantities of UDP traffic directed at subnets in order to discover each other. More info can be found at http://www.circlemud.org/~jelson/software/udpsend.html and http://www.ccd.bnl.gov/nss/tips/inoculan/index.html. Thanks to Jerry Leslie, NeoNET < leslie at clio dot rice dot edu>

 

1.2 What do the following source ports mean?

Ports 1-1024 are for reserved services, and almost never appear as the source. There are some exceptions, such as when connections come from NAT machines. See section 1.9 for some more details.

Ports closely after 1024 (i.e. 1024-5000) are the ones most commonly seen. These are the "dynamic" range that are assigned to applications that don't care what port they use for their connection.

 

Server	Client	Service	Description
1-5/tcp	dynamic	FTP	Ports 1-5 are indicative of a script called 'sscan'
20/tcp	dynamic	FTP	FTP servers usually transfer files from this port.
53	dynamic	FTP	DNS servers will send UDP responses from this port. You may also see TCP connections with source/destination ports of 53.
123	dynamic	S/NTP	The (Simple) Network Time Protocol (S/NTP) servers run at this port. They will also send broadcasts to this port.
27910-27961/udp	dynamic	Quake games	Quake (and Quake-derived games) usually run servers at these ports. Therefore, UDP packet from this range (and to this range) will usually be games.
61000+	dynamic	FTP	Ports above 61000 might come from machines behind a Linux NAT server called "IP Masquerade".

 

 

1.3 I'm seeing attempts on the same set of ports from widely varying sources all over the Internet.

This is due to a "decoy" scan, such as in 'nmap'. One of them is the attacker; the others are not.

Forensics and protocol analysis can be used to track down who this is. For example, if you ping each of the systems, you can match up the TTL fields in those responses with the connection attempts. This will at least point a finger at a decoy scan. (The TTLs should match; if not, then they are being spoofed). [Newer versions of scanner now randomize the attackers own TTL, making it harder to weed them out].

You can also attempt to go back further in your logs, looking for all the decoy addresses or people from the same subnets. You will often see that the attacker has actually connected to you recently, while the decoyed addresses haven't.

 

1.4 What are Trojan Horse probes?

The first stage of a Trojan Horse attack is to get the program on a user's machine. Typical techniques are:

• post the program to newsgroups claiming to be some other program
• spam mailing lists with the attached program
• post program to websites
• send via instant messenger programs and chat systems (ICQ, AIM, IRC, etc.)
• forge e-mail from the ISP (like AOL) with a hoax message asking somebody to run a program (such as a software update).
• copy to startup folder via "File and Print Sharing".

The next stage of the attack is to scan the Internet looking for machines that might be compromised. The problem is that most of the techniques outlined above don't tell the cracker/hacker where their victim machine is. Therefore, the cracker/hacker must scan the Internet looking for the machines they might have compromised.

This leads the condition where owners of firewalls (including personal firewalls) regularly see "probes" directed at their machines from crackers/hackers looking for these machines. However, if the machine hasn't been compromised, then these probes are not a problem. The probes cannot compromise the machine by themselves. Administrators can usually ignore these "attacks".

Typical ports used by these probes are listed below. In order to tell if your machine might be running one of these trojans, run the program "netstat -an" on your machine. Look for the ports that might be "listening" for incoming connections.

Port	Trojan
555	phAse zero
1243	Sub-7, SubSeven
3129	Masters Paradise
6670	DeepThroat
6711	Sub-7, SubSeven
6969	GateCrasher
21544	GirlFriend
12345	NetBus
23456	EvilFtp
27374	Sub-7, SubSeven
30100	NetSphere
31789	Hack'a'Tack
31337	BackOrifice, and many others
50505	Sockets de Troie

 

Resources: http://www.commodon.com/threat/threat-ports.htm

 

1.4.1 What is SubSeven (Sub-7) ?

Sub7 has become the most popular remote access trojan. At this time, it is the easiest-to-use and most powerful trojan. The reasons for this are:

• It is actively maintained/updated. Most other Trojans were created once then development stopped except for a couple of bug fixes.
• The program not only includes a scanner, but also can tell a slave machine to scan as well.
• The creator has a contest for cracked sites using Sub7.
• Supports "port redirection", so that any attack can be funneled through a victim's machines.
• Contains extensive tricks to play with ICQ, AOL IM, MSN Messenger, and Yahoo messenger, including password sniffing, posting messages, and other features.
• Extensive UI tricks, such as flipping the screen, talking through the victim's speaker, and spying on the victim's screen.

In short, it not only is an excellent hacking tool, the little "magic" tricks are designed to scare the <bleep> out of victims.

Sub7 is written by a hacker who calls himself "Mobman". His site can be reached at http://subseven.slak.org/.

Sub7 might use the following ports:

1243

The default connection port for older versions.

2772

Screen capture port

2773

Key logger port

6711

???

6776

I'm not sure what this port is for, but it has been claimed that this can serve as a "backdoor" in some versions. (Yes, a backdoor program with a backdoor to avoid password prompts).

7215

Port for the "matrix" chat program

27374

Another default port appearing in v2.0

54283

Spy port

 

1.9 DNS packets from low numbered ports

Q: I've seen many DNS requests from many low port numbers below 1024. Aren't they supposed to be reserved? Aren't they supposed to use 1024-65535 range?
A: These are coming from machines behind NAT firewalls. A NAT doesn't necessarily have the concept of reserved port numbers. thanks to Ryan Russell Ryan.Russell at sybase dot com

Q: My filters reject incoming packets with source ports below 1024, so the DNS lookups are failing.
A: Don't filter that way. Lots of firewalls have similar rules, but this is somewhat "misguided" since hackers/crackers can forge whatever ports they want.

Q: Are these