Page 1207 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

normally divided into smaller fragments when they’re sent over a
network, and the receiving system then puts the packet fragments

back together into their original state. However, a teardrop attack
mangles these packets in such a way that the system cannot put them
back together. Older systems couldn’t handle this situation and
crashed, but patches resolved the problem. Although current systems
aren’t susceptible to teardrop attacks, this does emphasize the
importance of keeping systems up-to-date. Additionally, intrusion
detection systems can check for malformed packets.

Land Attacks

A land attack occurs when the attacker sends spoofed SYN packets to
a victim using the victim’s IP address as both the source and
destination IP address. This tricks the system into constantly replying
to itself and can cause it to freeze, crash, or reboot. This attack was
first discovered in 1997, and it has resurfaced several times attacking
different ports. Keeping a system up-to-date and filtering traffic to

detect traffic with identical source and destination addresses helps to
protect against LAND attacks.

Zero-Day Exploit

A zero-day exploit refers to an attack on a system exploiting a
vulnerability that is unknown to others. However, security
professionals use the term in different contexts and it has some minor
differences based on the context. Here are some examples:

Attacker First Discovers a Vulnerability When an attacker

discovers a vulnerability, the attacker can easily exploit it because the
attacker is the only one aware of the vulnerability. At this point, the
vendor is unaware of the vulnerability and has not developed or
released a patch. This is the common definition of a zero-day exploit.

Vendor Learns of Vulnerability When vendors learn of a
vulnerability, they evaluate the seriousness of the threat and prioritize

the development of a patch. Software patches can be complex and
require extensive testing to ensure that the patch does not cause other
problems. Vendors may develop and release patches within days for
serious threats, or they may take months to develop and release a