June 2005

The chflags utility modifies the file flags of the listed files as specified by the flags operand. FreeBSD offers write protection, you need to to set special bit call immutable. Once this bit is setup no one can delete or modify file including root. And only root can clear the File immutable bit. You must […]

{ 3 comments }

The Internet Control Message Protocol (ICMP) has many messages that are identified by a “type” field. You need to use 0 and 8 ICMP code types. => Zero (0) is for echo-reply => Eight (8) is for echo-request. To enable ICMP ping incoming client request use following iptables rule (you need to add following rules […]

{ 25 comments }

Spoofing and bad address attack tries to fool the server and try to claim that packets had come from local address/network.

{ 19 comments }

A SYN flood is a form of denial-of-service attack in which an attacker sends a succession of SYN requests to a target’s system. This is a well known type of attack and is generally not effective against modern networks. It works if a server allocates resources after receiving a SYN, but before it has received […]

{ 17 comments }

You would like to block outgoing access to particular remote host/ip or port for all or selected service/port. In this quick tutorial I will explain how to use iptables to block outgoing access.

{ 25 comments }

Sometime it is necessary to block incoming connection or traffic from specific remote host. iptables is administration tool for IPv4 packet filtering and NAT under Linux kernel. Following tip will help you to block attacker or spammers IP address. How do I block specific incoming ip address? Following iptable rule will drop incoming connection from […]

{ 14 comments }

Recently we had lot of discussion regarding this issue. How to remove files securely so that it cannot be undeleted. Peter Gutmann paper “Secure Deletion of Data from Magnetic and Solid-State Memory” has very good information. Here are some commands/tools available under Debian GNU/Linux (it should work with other Linux distributions) to delete file securely. […]

{ 6 comments }