In-depth analysis of common Sniffit problems and prevention strategies

Article Title: in-depth analysis of common Sniffit problems and prevention strategies. Linux is a technology channel of the IT lab in China. Includes basic categories such as desktop applications, Linux system management, kernel research, embedded systems, and open source.
1. sniffit is both an excellent management tool and a dangerous intrusion tool. The administrator can check what is transmitted in the network, learn the working methods of various TCP/IP protocols, and be exploited by attackers, mainly to record passwords.
　　
2. Working principle: why can I check the password and the data that is not sent to myself?
　　
In A typical LAN environment (two users A and B connected to the shared HUB), the working principle of the shared HUB is as follows, all TCP/IP requests sent by user A are broadcast on each port of the HUB. Normally, B does not receive data from these destination addresses, however, once we run a sniffit-type listening tool on machine B, we can set the NIC to the status in the third mode (the first two are tcp and udp modes ), in this status, the network adapter receives all the data, whether sent to itself or not, and directly transmits the data to the upper-layer application layer for processing by the corresponding software such as sniffit.
　　
3. Common usage
　　
A. Check the password for telnet, ftp, and pop3:
　　
# Sniffit-a-A.-p 23-B-t 192.168.11 .@
# Sniffit-a-A.-p 110-B-t 192.168.11.1 (pop3 server)
　　
B. View http header information
　　
# Sniffit-a-A.-p 80-B-s 1.2.3.4 (1.2.3.4 is the external address of the firewall)
　　
C. Record output to file
　　
# Sniffit-p 21-l 0-B-s 192.168.11.2 &
　　
D. View icmp messages
　　
# Sniffit-p icmp-B-s 192.168.1.2
　　
E. Interactive Interface
　　
# Sniffit-I
　　
F. Check the machines that issue name broadcasts in this section.
　　
# Sniffit-a-A.-P udp-p 137-B-s 192.168.11.255
　　
G. Pay attention to the firewall situation
To check the eth1 package on the firewall Intranet card, you may need to set the-F eth1 parameter, because the default sniffit is assumed to be eth0.
　　
　　
4. What information is sensitive and easy to detect?
Telnet, ftp, and pop3 passwords are transmitted in plain text and are easy to detect. The basic username/password authentication of apache is also a UU-encoded password, which is also easy to detect.
　　
5. How to stop it?
Hardware: Do not use a common shared HUB instead of a vswitch. Currently, only vswitches and vrouters can block sniffit.
Software: use encrypted TCP/IP connection, like ssh/scp, instead of telnet/ftp/pop3, and use MD5 apache authentication.
　　
6. Scope:
Valid only in the logical subnet, not across subnets, because broadcast is not transmitted by the router, but if sniffit is run on the server, any method is invalid. For the firewall, generally, sniffit attacks are second-level attacks, that is, first getting a common account and then exploring more passwords.
　　
7. How can I determine if someone is using sniffit?
You can check the network interface (ifconfig) and check whether it is in the mixed mode to check whether it has been intruded and sniffit is installed. Only the local machine is allowed.