How to lock user account (disable user login temporarily) in UNIX – comparison of 4 solutions

1) Proper way to lock UNIX user account is: bash# passwd -l user – It will add some special character (! or *) in the beginning of his password (to /etc/shadow) To unlock again: bash# passwd -u user User will get “Login incorrect” while logging in: planar login: user Password: Login incorrect planar login: – – [...]

Network attack: Reflection SYN attack

Network attack: reflection SYN attack Amplified SYN attack (“reversed” SYN attack) aka. reflection SYN attack. The trick is to massively initiate connections with random servers (and their open TCP ports) with spoofed source IP address – of the victim. In detail: 1) You send TCP packet with SYN flag to somewebserver.com:80 with spoofed source address of [...]

SSH Login without password – Useful little shell script

This script is very useful when you have to manage lot of machines, and you are tired of typing passwords to login – type the password just once! – – – – – – – – – – – – – – – – – – – The script sshprep.sh: #!/bin/bash cat ~/.ssh/id_dsa.pub | ssh root@${1} [...]

ARP poisoning with nemesis

ARP poisoning with nemesis In this practical example, we are going to use tool called nemesis project - raw packet injector. In order to sniff all communication (in/out), we must poison both hosts). Then all communication will go through us. – – – – – – – – – – – – – – – – – [...]

Secure Sockets Layer (SSL)

  Secure Sockets Layer (SSL) is the most widely used technology for providing a secure communication between the web client and the web server.Most of us are familiar with many sites such as Gmail, Yahoo etc. using httpsprotocol in their login pages.When we see this, we may wonder what’s the difference between http and https.In simple words HTTP protocol is used [...]

The Hole

The Concept of the Hole Before I examine different types of holes, I’d like to define the term hole. A hole is any feature of hardware or software that allows unauthorized users to gain access or increase their level of access without authorization. I realize this is a broad definition, but it is accurate. A [...]

An Introduction to Breaching a Server Internally

An internal breach can be defined as any breach of security on a network to which the hacker or cracker has some access, on which he is a user with a valid account, or where he is a member of a company that maintains such a network. Whether you are a victim or a perpetrator [...]

Spoofing Attacks

There has never been more controversy about a cracking technique than the controversy surrounding IP spoofing. IP spoofing is the most talked about and least understood method of gaining unauthorized entry to a computer system. For example, a well publicized spoofing case occurred in December, 1994. John Markoff, in his article that appeared in The [...]

Telnet-Based Attacks

 The Telnet protocol was first comprehensively defined by Postel in 1980. In RFC 764, Postel wrote: The purpose of the Telnet protocol is to provide a fairly general, bi-directional, eight-bit byte oriented communications facility. Its primary goal is to allow a standard method of interfacing terminal devices and terminal-oriented processes to each other. It is [...]

Levels of Attack

An attack is any unauthorized action undertaken with the intent of hindering, damaging, incapacitating, or breaching the security of your server. Such an attack might range from a denial of service to complete compromise and destruction of your server. The level of attack that is successful against your network depends on the security you employ. [...]