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The Rose Fragmentation Attack was conceived through a need to create disruption in a network. This attack is a combination of the SYN attack and the "Unknown" ICMP attack. The following link is for an in-depth analysis of the attack.
* Evasions exist in every protocol
* Evasions can be combined together to create new evasions
* The order of combined evasions is important
* The number of different evasion combinations is enormous
Administratively shut down a switch port interface associated with a system from which
attacks are being launched.
Look for the nop opcode other than Ox90 to defend against the polymorphic shellcode
problem.
Perform "bifurcating analysis," in which the monitor deals with ambiguous traffic
streams by instantiating separate analysis threads for each possible interpretation
of the ambiguous traffic.
Maintain security vulnerability awareness, patch vulnerabilities as soon as possible, and
wisely choose the IDS based on t he network topology and network traffic received.
Generate TCP RST packets to tear down malicious TCP sessions, any issues of several
available ICMP error code packets in response to malicious UDP traffic.
Interact with the external firewall or router to add a general rule to block all
communication from individual IP addresses or entire networks.
Implement a "traffic normalizer": a network forwarding element that attempts to
eliminate ambiguous network traffic and reduce the amount of connection state that
the monitor must maintain.
Ensure that IDSs normalize fragmented packets and allow t hose packets to be
reassembled in t he proper order, which enables the IDS to look at the information just
as the end host can see it.
Keep updating the IDS system and firewall software regularly.
Maintain security vulnerability awareness, patch vulnerabilities as soon as possible, and
wisely choose the IDS based on the network topology and network traffic received.
Change the TIL field to a large value, ensuring that the end host always receives the
packets. In such case, attackers cannot slip information to the IDS. As a result, that data
never reaches the end host, leaving the end host with the malicious payload.
Bypassing a Firewall through the ACK Tunneling Method
ACK tunneling allows tunneling a backdoor application with TCP packets with the ACK bit set.
The ACK bit is used to acknowledge receipt of a packet. Some firewalls do not check packets
with the ACK bit set because ACK bits are supposed to be used in response to legitimate traffic
that is already being allowed through. Attackers use this as an advantage to perform ACK
tunneling. Tools such as AckCmd (http://ntsecurity.nu) can be used to implement ACK
tunneling.
IP Address Spoofing
IP address spoofing or IP spoofing is one of the ways that an attacker tries to evade
firewall restrictions. IP spoofing is a technique where the attacker creates Internet protocol
packets by using a forged IP address and gains access over the system or network without any
authorization. The attacker spoofs the messages and they appear to be sent from a reliable
source. Thus, the attacker succeeds in impersonating others' identities with help of IP spoofing.
This technique is used to hide their true attack.
Source Routing
Using this technique, the sender of the packet designates the route that a packet
should take through the network in such a way that the designated route should bypass the
firewall node. Using this technique the attacker can evade the firewall restrictions.
When these packets travel through the nodes in the network, each router will check the IP
address of the destination and choose the next node to forward them.
Tiny Fragments
The attacker uses the IP fragmentation technique to create extremely small
fragments and force the TCP header information into the next fragment. This may result in a
case whereby the TCP flags field is forced into the second fragment, and filters will be unable to
check these flags in the first octet thus ignoring them in subsequent fragments.
Attackers hope that only the first fragment is examined by the filtering router (firewall) and the
remaining fragments are passed through. This attack is used to avoid user defined filtering rules
and works when the firewall checks only for the TCP header information.
Bypass Blocked Sites Using IP Address in Place of URL
You can also evade firewall restrictions by typing the IP address of t he blocked site instead of
its domain names. This allows you to access the restricted or blocked sites. You need to use
some tools to convert the target domain name into its IP address.
Bypass Blocked Sites Using Anonymous Website Surfing Sites.
Anonymous website surfing sites help you to surf the Internet anonymously and to unblock
blocked sites. i.e., evade firewall restrictions. By using these sites, you can surf restricted sites
anonymously, i.e., without using your IP address on the Internet. There are a number of
anonymous website surfing sites available on the Internet. Some websites provide options to
encrypt the URLs of websites.
Bypassing a Firewall through the ICMP Tunneling Method
By using a proxy server, you can also bypass the firewall restriction imposed by aparticular organization. To evade t he firewall restrict ions using a proxy server, follow thesesteps:
Find an appropriate proxy server.
On the Tools menu of any Internet browser, go to LAN of Network Connections tab, and
then click LAN/Network Settings.
Under Proxy server settings, select t he use a proxy server for the LAN.
In the Address text box, type the IP address of the proxy server.
In the Port text box, type t he port number t hat is used by the proxy server for client
connections (by default, 8080).
Click to select the bypass proxy server for local addresses check box if you do not want
the proxy server computer to be used when connected to a computer on the local
network.
Click OK to close the LAN Settings dialog box.
Click OK again to close the Internet Options dialog box.
Bypassing a Firewall through the ACK Tunneling Method
ICMP tunneling allows tunneling a backdoor shell in the data portion of ICMP Echo packets. RFC
792, which delineates ICMP operation, does not define what should go in the data portion . The
payload portion is arbitrary and is not examined by most of the firewalls, thus any data can be
inserted in the payload portion of the ICMP packet, including a backdoor application. Some
administrators keep ICMP open on their firewall because it is useful for tools like ping and
traceroute.
Bypassing a Firewall through the HTTP Tunneling Method
This method can be implemented if the target company has a public web server with port 80
used for HTTP traffic, that is unfiltered on its firewall. Many firewalls do not examine the
payload of an HTTP packet to confirm that it is legitimate HTTP traffic, thus it is possible to
tunnel traffic inside TCP port 80 because it is already allowed.
Bypassing a Firewall through a MITM Attack
The following steps illustrate an example scenario of how an attacker bypasses a firewall through an MITM attack:
You should footprint the target by using various tools such as Sam Spade, nslookup, traceroute,
Nmap, and neotrace to learn about a system, its remote access capabilities, its ports and
services, and the other aspects of its security.
Step 2: Perform port scanning
You should perform port scanning to detect the firewall to determine the available ports that
uniquely identify the firewalls. If the firewall is detected, then disable a trusted host or perform
banner grabbing to detect the firewall.
Step 3: Perform banner grabbing
You should perform the banner grabbing technique to detect the services run by the firewall. If
the firewall is detected, then disable a trusted host or perform firewalking to detect the
firewall.
Step 4: Perform Firewalking
You should use the firewalking technique to determine access information on the firewall when
probe packets are sent. If a firewall is detected, then disable a trusted host.
Step 6: Perform IP address spoofing
You should perform IP address spoofing to gain unauthorized access t o a computer or a
network.
Step 7: Perform source routing
Step 8: Use an IP address in place of URL
Step 9: Perform a fragmentation attack
You should perform an IP fragmentation ion at tack to force the TCP header information into the
next fragment in order to bypass the firewall.
Step 10 : Use anonymous website surfing sites
You should use anonymous website surfing sites to hide your identity from the Internet.
Step 11 : Use proxy servers
You should use proxy servers that block the actual IP address and display another, thereby
allowing access to the blocked website.
Step 12 : Perform ICMP tunneling
You should perform ICMP tunneling to tunnel a backdoor application in the data portion of
ICMP Echo packets.
Step 14 : Perform ACK tunneling
You should perform ACK tunneling using tools such as AckCmd to tunnel backdoor application
with TCP packets with t he ACK bit set.
Step 15 : Use external systems
Step 16: Perform MITM Attack
You should perform an MITM attack in order to own corporate the DNS server or to spoof DNS
replies to it.
The National Institute of Standards and Technology (NIST) 800-10 divides firewalls into three basic types:
Packet filters:
On the Internet, packet filtering is the process of passing or blocking packets at a network interface based on source and destination addresses, ports, or protocols. The process is used in conjunction with packet manglingand Network Address Translation (NAT). Packet filtering is often part of a firewallprogram for protecting a local network from unwanted intrusion.
n a software firewall, packet filtering is done by a program called a packet filter. The packet filter examines the header of each packet based on a specific set of rules, and on that basis, decides to prevent it from passing (called DROP) or allow it to pass (called ACCEPT).
There are three ways in which a packet filter can be configured, once the set of filtering rules has been defined. In the first method, the filter accepts only those packets that it is certain are safe, dropping all others. This is the most secure mode, but it can cause inconvenience if legitimate packets are inadvertently dropped. In the second method, the filter drops only the packets that it is certain are unsafe, accepting all others. This mode is the least secure, but is causes less inconvenience, particularly in casual Web browsing. In the third method, if the filter encounters a packet for which its rules do not provide instructions, that packet can be quarantined, or the user can be specifically queried concerning what should be done with it. This can be inconvenient if it causes numerous dialog boxes to appear, for example, during Web browsing.
Stateful inspection:
Stateful inspection has largely replaced an older technology, static packet filtering. In static packet filtering, only the headers of packets are checked -- which means that an attacker can sometimes get information through the firewallsimply by indicating "reply" in the header. Stateful inspection, on the other hand, analyzes packets down to the application layer. By recording session information such as IP addresses and port numbers, a dynamic packet filter can implement a much tighter security posture than a static packet filter can.
Stateful inspection monitors communications packets over a period of time and examines both incoming and outgoing packets. Outgoing packets that request specific types of incoming packets are tracked and only those incoming packets constituting a proper response are allowed through the firewall.
In a firewall that uses stateful inspection, the network administrator can set the parameters to meet specific needs. In a typical network, ports are closed unless an incoming packet requests connection to a specific port and then only that port is opened. This practice prevents port scanning, a well-known hacking technique.
Proxy:
That's an important distinction and it requires a little insight into the history of these devices. Proxy firewalls, or application gateway firewalls, are a fairly recent addition to mainstream security environments. Until a few years ago, the stateful inspection firewall was the most advanced firewall protection. While stateful firewalls can monitor open connections, they cannot inspect application layer traffic. Therefore, if you were to allow HTTP traffic through your firewall, a stateful inspection firewall would not prevent an HTTP-based attack. Proxy firewalls, on the other hand, combine stateful inspection technology with the ability to perform deep application inspections. They also analyze layer 7 protocols, such as HTTP and FTP and monitor traffic for additional signs of attack. To make this work, the firewall must act as a proxy; that is, the client opens a connection with the firewall (usually unbeknownst to the client) and the firewall opens a separate connection to the server on the client's behalf.
Proxy servers, however, don't provide the benefits of a firewall. Like proxy firewalls, they act as a middleman for connections, but they don't provide stateful inspection or other firewall technology. They're generally used to provide content filtering and performance enhancements (such as caching) for local user's Web traffic. Since most proxy firewalls can provide all of the benefits of a proxy server, administrators typically use dedicated proxy servers where they wish to remove the performance load from the firewall.
Firewalls provide essential protection to the computers against viruses, privacy
threats, objectionable content, hackers, and malicious software when networked or connected
to the Internet. A firewall monitors running applications that access the network. It analyzes
downloads and warns you if downloading a malicious file, stops it from infecting your PC. A few
of the firewalls that provide system protection are listed as follows:
It tries to identify events that indicate an abuse of a system. It is achieved by creating models of intrusions. Incoming events are compared with intrusion models to make a detection decision. While creating signatures, the model must detect an attack without disturbing the normal traffic on the system. Attacks, and only attacks, should match the model or else false alarms can be Generated
The simplest form of signature recognition uses simple pattern matching to compare
the network packets against binary signatures of known attacks. A binary signature may
be defined for a specific portion of the packet, such as the TCP flags.
Signature recognition can detect known attacks. However, t here is a possibility that
other packets that match might represent the signature, triggering bogus signals.
Signatures can be customized so that even well-informed users can create them.
Signatures that are formed improperly may trigger bogus signals. In order to detect
misuse, the number of signatures required is huge. The more t he signatures, the more
attacks can be detected, though traffic may incorrectly match with the signatures,
reducing the performance of the system.
The bandwidth of the network is consumed with the increase in the signature database.
As the signatures are compared against those in the database, there is a probability that
the maximum number of comparisons cannot be made, resulting in certain packets
being dropped.
New virus attacks such as ADMutate and Nimda create the need for multiple signatures
for a single attack. Changing a single bit in some attack strings can invalidate a signature
and create the need for an entirely new signature.
Despite problems with signature-based intrusion detection, such systems are popular
and work well when configured correctly and monitored closely
Anomaly Detection(not-use detection)
The model consists of a database of anomalies. Any event that is identified with the database in considered an anomaly. Any deviation from normal use is labeled an attack. Creating a model of normal use is the most difficult task in creating an anomaly detector.
In the traditional method of anomaly detection, important data is kept for checking
variations in network traffic for the model. However, in reality, there is less variation in
network traffic and too many statistical variations making these models imprecise;
some events labeled as anomalies might only be irregularities in network usage.
In this type of approach, the inability to instruct a model thoroughly on the normal
network is of grave concern. These models should be trained on the specific network
that is to be policed.
Protocol Anomaly Detection
Protocol anomaly detection is based on the anomalies specific to a protocol. This
model is integrated into the IDS model recently. It identifies the TCP/IP protocol specific flaws
in the network. Protocols are created with specifications, known as RFCs, for dictating proper
use and communication. The protocol anomaly detector can identify new attacks.
Protocol anomaly detection systems are easier to use because they require no signature
updates
There are new attack methods and exploits that violate protocol standards being
discovered frequently.
The pace at which t he malicious signature attacker is growing is incredibly fast. But the
network protocol, in comparison, is well defined and changing slowly. Therefore, the
signature database must be updated frequently to detect attacks.
Protocol anomaly detection systems are easier to use because they require no signature
updates
Protocol anomaly detectors are different from the traditional IDS in how they present
alarms.
The best way to present alarms is to explain which part of the state system was
compromised. For this, the IDS operators have to have a thorough knowledge of the
protocol design; the best way is the documentation provided by the IDS.
Snort has three primary uses: a straight packet sniffer like tcpdump, a packet logger (useful fornetwork traffic debugging,etc.), or a full-blown network intrusion prevention system.
TippingPoint IPS is inserted seamlessly and transparently into the network; it is an in-line device. Each packet is thoroughly inspected to determine whet her it is malicious or legitimate. It provides performance, application, and infrastructure protection at gigabit speeds through total packet inspection
The IDS does not know that the end-system would reject that packet. Then the attacker can for example insert blinders within a malicious string (sent byte by byte).
The IDS would accept all bytes and recognizes the string as harmless
The host only accepts those bytes that belong to the malicious
sequence
When UDP is used, the blinders could be data-grams with wrong checksum (which are only dropped by the destination host). Widespread vulnerability! Therefore also the IDS must check the checksum of each packet, etc. . .
Insertion---The IDS gets more packets than the destination.
Evasion
If the IDS is more strict, then this could lead to evasion attacks:
For example, if the malicious sequence is sent byte-by-byte, and one byte is rejected by the IDS, the IDS cannot detect the attack. Generally, the IDS rejects packets, the victim does not.
Evasion: The IDS gets less packets than the destination.
Denial-of-Service
An adversary can evade detection by disabling or overwhelming the IDS. This can be accomplished by exploiting a bug in the IDS, using up computational resources on the IDS, or deliberately triggering a large number of alerts to disguise the actual attack. The tools 'stick' and 'snot' were designed to generate a large number of IDS alerts by sending attack signatures across the network, but will not trigger alerts in IDSs that maintain application protocol context.
Obfuscation
An IDS can be evaded by obfuscating or encoding the attack payload in a way that the target computer will reverse but the IDS will not. In the past, an adversary using the Unicode character could encode attack packets that an IDS would not recognize but that an IIS web server would decode and become attacked.
subsequent avoidance of such can lead to a successful intrusion
False Positive Generation
This mode does not actually attack the target. This is to deliberately trigger a false IDSs alarm. This will cause the IDS to generate a large number of false detection reports. This is aimed at creating network "noise" in order to disguise malicious network activity.
Session Splicing
Session splicing is an IDS evasion technique that exploits how some IDSes do not reconstruct sessions before performing pattern matching on the data. This is a network-level evasion tactic that divides the string across several packets. The data in the packet is divided into small portions of bytes in order to evade signature detection. Many IDSes reassemble communication streams, so if a packet is not received within a reasonable amount of time, many IDSes stop reassembling and handling that particular stream.
Unicode Evasion Technique
Unicode is a character representation that gives each character a unique identifier for each written language to facilitate the uniform computer representation of each language. This is an issue for IDS technology because it is possible to have multiple representation of a single character.
Fragmentation Attack
Attackers break the single Internet protocol data-gram into multiple packets of small size. IDS fragmentation reassembly timeout is less than fragmentation reassembly timeout of the victim.
Overlapping Fragments
An IDS evasion technique is to craft a series of packets with TCP sequence numbers configured to overlap. In an Overlapping fragment attack the packet start in the middle of another packet.
Time-to-live attacks
Each IP packet has a field called Time to Live(TTL), which indicates how many more hopes the packet should be allowed to make before being discarded or returned. Each router along a data path decrements this value, by one. When a router decrements this value to zero, it drops the packet and send an ICMP alert notification. The attacker breaks into this fragment and reassemble will remaining undetected by the IDS.
Invalid RST packets
The TCP protocol use checksum to ensure that communication is reliable. A checksum is added to every transmitted segment and it is checked at the receiving end. When a checksum differs from the checksum expected by the receiving host the packet is dropped at the receiver's end. Attackers can use this feature to elude detection by sending
RST packets with an invalid checksum, which causes the IDS to stop processing the stream because the IDS thinks the communication session has ended.
Polymorphic Shell code
Most IDSes contain signatures for commonly used strings within malicious shellcode. This is easily bypassed by using encoded shellcode containing a stub that decodes the shellcode that follows. This hides the actual shellcode, making signature detection almost useless.
ASSCI Shell code
ASSCI shellcode contains only characters contained within the ASCII standard. This form of shelcode allows attackers to bypass commonly enforced restrictions within string input code. It also helps attackers bypass IDS pattern matching signatures because strings are hidden within the shellcode in a similar fashion to polymorphic shellcode.
Additional Types of Evasion
Encryption
When the attacker has already established an encrypted session within the victim, it results in the most effect evasion attack.
Flooding
The attackers send loads of unnecessary traffic to produce noise, and if the IDS does not analyze the traffic properly, it may slip by undetected.
You should try to find and disable the trusted host so that the targeted host thinks that the
traffic that the attacker will generate emanates from there.
Step 2: Perform an insertion attack
Step 3: Implement the evasion technique
Step 4: Perform a denial-of-service attack
Step 5: Obfuscate or encode the attack payload
You should implement the obfuscating technique to encode attack packets that the IDS would
not detect but an liS web server would decode and be attacked.
Step 6: Perform the false positive generation technique
You should use the false positive generation technique to create a great deal of log "noise" in
an attempt to blend real attacks with the false.
Step 7: Perform the Session Splicing Technique
You should implement the session splicing technique to stop the IDS by keeping the session
active longer than IDS will spend on reassembling it.
Step 8 : Perform the Unicode evasion technique
You should implement the Unicode evasion technique to evade IDSes as it is possible to have
multiple representations of a single character.
Step 9: Perform a fragmentation attack
Step10: Perform the overlapping fragments technique
You should use overlapping fragments technique to craft a series of packets with TCP
sequence numbers configured to overlap.
Step 11: Perform a Time-To-live attack
Step 12: Perform the invalid RST packets technique
You should use the invalid RST packets technique to evade detection by sending RST packets
with an invalid checksum that causes the IDS to stop processing the stream.
Step 13: Perform the urgency flag technique
You should use the urgency flag technique to evade IDSrd as some IDSrds do not consider the
TCP protocol's urgency feature.
Step 14 : Perform the polymorphic shellcode technique
You should use the polymorphic shellcode technique to hide the shellcode by encrypting it in a
simplistic form that is difficult for IDS to identify that data as a shellcode.
Step 15: Perform the ASCII shellcode technique
You should perform the ASCII shellcode technique to bypass IDS pattern matching signatures
because strings are hidden within the shellcode as in a polymorphic shellcode.
Step 16: Perform an Application-layer attacks
You should try to perform Application-level attacks as many lOSes will have no way to check the
compressed file format for signatures.
Step 17: Perform encryption and flooding techniques
You should try encryption and flooding attacks with the victim or send loads of unnecessary
traffic to produce noise that can't be analyzed by the IDS.
Step 18: Perform a post-connection SYN attack
Step 19: Perform a pre-connection SYN attack
Step 20: Document all the results obtained from this test
You should perform a fragmentation attack with IDS fragmentation reassembly timeout less
and more than t hat of the victim.
Are maintained by both the tester and the analyst for all data gathered to support a valid assessment through non-privileged testing. This implies that if too little or improper data has been gathered then it may not be possible to provide a valid risk assessment and the tester should therefore rely on best practices, the client’s industry regulations, the client’s business justifications, the client’s security policy, and the legal issues for the client and the client’s regions for doing business.
Risk Evaluation
Risk means that limits in the security presence will have a detrimental effect on people, culture information, processes, business, image, intellectual property, legal rights, or intellectual capital. This manual maintains four dimensions in testing for a minimal risk state environment:
Safety
All tests must exercise concern for worst case scenarios at the greatest expenses. This requires the tester to hold above all else the regard for human safety in physical and emotional health and occupation.
Privacy
All tests must exercise regard for the right to personal privacy regardless of the regional law. The ethics and understanding for privacy are often more advanced then current legislation.
Practicality
All tests must be engineered for the most minimal complexity, maximum viability, and deepest clarity.
Usability
All tests must stay within the frame of usable security. That which is most secure is the least welcoming and forgiving. The tests within this manual are performed to seek a usable level of security (also known as practical security).
