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Please note that this site does not process or store your credit card information. Your credit card purchase will be processed online by well-known secure credit card processors. IDM Awards. Esmail, H. Characterization of progressive HIV-associated tuberculosis using 2-deoxy[ 18 F]fluoro-D-glucose positron emission and computed tomography. Nature Medicine 22 10 HIV-tuberculosis-associated immune reconstitution inflammatory syndrome is characterized by Toll-like receptor and inflammasome signalling.

Nature Communications 6 , Anderson, S. Using a server directive with the HST record gained from a whois query, you can discover the other domains for which a given DNS server is authoritative. The following steps show you how. Execute a domain query as detailed earlier.

Locate the first DNS server. This database maintains spe- cific network blocks that an organization owns. It is particularly important to perform this search to determine if a system is actually owned by the target organization or if it is being co-located or hosted by another organization such as an ISP. Querying the ARIN database is a particularly handy query because it is not subject to the record limit implemented by Network Solutions.

Thus, we can conclude that this is a valid network owned by Acme Networks. One of the easiest ways to search for ARIN information is from their web site. You may uncover a domain that you were unaware of. NET U Countermeasure: Public Database Security Much of the information contained in the various databases discussed thus far is geared at public disclosure.

Administrative contacts, registered net blocks, and authoritative name server information is required when an organization registers a domain on the Internet. However, security considerations should be employed to make the job of attack- ers much more difficult. Thus, first ensure that the information listed in the database is accurate. Update the administrative, technical, and billing contact infor- mation as necessary. Furthermore, consider the phone numbers and addresses listed.

These can be used as a starting point for a dial-in attack or for social engineering purposes. In addition, we have seen several organizations list a fictitious administrative contact, hoping to trip up a would-be social engineer. If any employee receives an email or calls to or from the fictitious contact, it may tip off the information security department that there is a potential problem.

Another hazard with domain registration arises from the way that some registrars allow updates. For example, the current Network Solutions implementation allows automated online changes to domain information. Shockingly, the default authentication method is the FROM field via email. The security implications of this authentication mechanism are prodigious. Essentially, anyone can trivially forge an email address and change the infor- mation associated with your domain, better known as domain hijacking.

It is important to choose a more secure solution like password or PGP authentication to change domain information. Moreover, the administrative or technical contact is required to establish the authentication mechanism via Contact Form from Network Solutions. Step 3. DNS is a distributed database used to map IP addresses to hostnames and vice versa. If DNS is configured insecurely, it is possible to obtain revealing information about the organization.

A zone transfer allows a secondary master server to update its zone database from the primary master. This provides for redundancy when running DNS, should the primary name server become unavailable.

Many DNS servers, however, are misconfigured and provide a copy of the zone to anyone who asks. In this case, internal hostnames and IP addresses are disclosed to the attacker. While there are many different tools to perform zone transfers, we are going to limit the discussion to several common types. A simple way to perform a zone transfer is to use the nslookup client that is usually provided with most UNIX and NT implementations.

However, our DNS server Thus, we need to manually tell nslookup which DNS server to query. Recall that we found this information from our domain whois lookup per- formed earlier.

Next we set the record type to any. This will allow you to pull any DNS records avail- able man nslookup for a complete list. Finally, we use the ls option to list all the associated records for the domain. The —d switch is used to list all records for the domain. After completing the zone transfer, we can view the file to see if there is any interesting information that will allow us to target specific systems.

We see that for each entry we have an A record that denotes the IP address of the system name located to the right. Since we saved the results of the zone transfer to an output file, we can easily manipulate the results with UNIX pro- grams like grep, sed, awk, or perl. Suppose we are experts in SunOS or Solaris. Suppose we wanted to find test systems, which happen to be a favorite choice for at- tackers.

These are just a few simple exam- ples. Most intruders will slice and dice this data to zero-in on specific system types with known vulnerabilities.

Keep a few points in mind. The aforementioned method only queries one nameserver at a time. This means that you would have to perform the same tasks for all nameservers that are authoritative for the target domain. In addition, we only queried the Acme.

If there were subdomains, we would have to perform the same type of query for each subdomain for example, greenhouse.

This usually indicates that the server has been configured to disallow zone transfers from unauthorized users. Thus, you will not be able to perform a zone transfer from this server. However, if there are multi- ple DNS servers, you may be able to find one that will allow zone transfers. Now that we have shown you the manual method, there are plenty of tools that speed the process, including, host, Sam Spade, axfr, and dig.

The host command comes with many flavors of UNIX. Some simple ways of using host are as follows: host -l Acme. A num- ber of Windows products provide the same information, as shown in Figure This Figure In addition, you can even pass top-level do- mains like com and edu to get all the domains associated with com and edu, respectively.

However, this is not recommended. Often in a commercial environment, mail is handled on the same system as the firewall, or at least on the same network. So we can use host to help harvest even more information.

The preceding information appears to cross-reference with the whois ARIN search we previously performed. Thus, we can feel comfortable that this is a network we should be investigating. U Countermeasure: DNS Security DNS information provides a plethora of information to attackers, so it is important to reduce the amount of information available to the Internet. From a host configuration perspec- tive, you should restrict zone transfers to only authorized servers.

For modern versions of BIND, the allow-transfer directive in the named. For other nameservers, you should consult the documentation to determine what steps are necessary to restrict or disable zone transfers.

On the network side, you could configure a firewall or packet-filtering router to deny all unauthorized inbound connections to TCP port Since name lookup requests are UDP and zone transfer requests are TCP, this will effectively thwart a zone transfer at- tempt. In most cases, DNS queries will easily fit within bytes. Restricting zone transfers will increase the time necessary for attackers to probe for IP addresses and hostnames.

However, since name lookups are still allowed, attackers could manually perform lookups against all IP addresses for a given net block. There- fore, configure external name servers to provide information only about systems di- rectly connected to the Internet. External nameservers should never be configured to divulge internal network information. This may seem like a trivial point, but we have seen misconfigured nameservers that allowed us to pull back more than 16, internal IP addresses and associated hostnames.

However, HINFO records make it that much easier to programmatically cull potentially vulnerable systems. Step 4. Network Reconnaissance Now that we have identified potential networks, we can attempt to determine their net- work topology as well as potential access paths into the network.

In Windows NT, it is spelled tracert due to the 8. Traceroute is a diagnostic tool originally written by Van Jacobson that lets you view the route that an IP packet follows from one host to the next. Each router that handles the packet is required to decrement the TTL field. Thus, the TTL field effectively becomes a hop counter. We can use the functionality of traceroute to determine the exact path that our packets are taking. As mentioned previously, traceroute may allow you to discover the network topology employed by the target network, in addition to identifying access control devices application-based firewall or packet-filtering routers that may be filtering our traffic.

The packets go through the various hops without being blocked. From our earlier work, we know that the MX record for Acme. Thus, we can assume this is a live host and that the hop before it 4 is the border router for the organization. Hop 4 could be a dedicated application-based firewall, or it could be a simple packet-filtering device—we are not sure yet.

Generally, once you hit a live system on a network, the system before it is a device performing rout- ing functions for example, a router or a firewall. This is a very simplistic example. But in a complex environment, there may be multiple routing paths, that is, routing devices with multiple interfaces for example, a Cisco se- ries router. Moreover, each interface may have different access control lists ACLs applied.

In many cases, some interfaces will pass your traceroute requests, while others will deny it because of the ACL applied.

Thus, it is important to map your entire network using traceroute. After you traceroute to multiple systems on the network, you can begin to create a network diagram that depicts the architecture of the Internet gateway and the loca- tion of devices that are providing access control functionality.

We refer to this as an access path diagram. Thus, your mileage may vary using each tool if the site blocks UDP vs. ICMP and vice versa. Another interesting option of traceroute includes the —g option that allows the user to specify loose source routing. Thus, if you believe the target gateway will accept source-routed packets which is a car- dinal sin , you might try to enable this option with the appropriate hop pointers see man traceroute in UNIX for more information.

There are several other switches that we need to discuss that may allow you to bypass access control devices during our probe. The —p n option of traceroute allows you to specify a starting UDP port number n that will be incremented by 1 when the probe is launched. Thus, we will not be able to use a fixed port number without some modification to traceroute. This allows you to force every packet we send to have a fixed port number, in the hopes that the access control device will pass this traffic.

Since many sites allow inbound DNS queries, there is a high probability that the access control device will allow our probes through. Thus, we can probe systems behind the access control device just by sending out probes with a destination port of UDP Additionally, if you send a probe to a system that has UDP port 53 listening, you will not receive a normal ICMP unreach- able message back.

Thus, you will not see a host displayed when the packet reaches its ul- timate destination. Most of what we have done up to this point with traceroute has been com- mand-line oriented. VisualRoute provides a graphical depiction of each network hop and integrates this with whois queries. VisualRoute, depicted in Figure , is appealing to the eye, but does not scale well for large-scale network reconnaissance. There are additional techniques that will allow you to determine specific ACLs that are in place for a given access control device.

Firewall protocol scanning is one such tech- nique and is covered in Chapter VisualRoute, the Cadillac of traceroute tools, provides not just router hop information but also geographic location, whois lookups, and web server banner information. U Countermeasure: Thwarting Network Reconnaissance In this chapter, we only touched upon network reconnaissance techniques. We shall see more intrusive techniques in the following chapters.

There are, however, several counter- measures that can be employed to thwart and identify the network reconnaissance probes discussed thus far. Many of the commercial network intrusion detection systems NIDSes will detect this type of network reconnaissance. We have purposely limited our discussion to common tools and techniques.

Bear in mind, however, that new tools are released daily. Moreover, we chose a simplistic example to illustrate the concepts of footprinting. Often you will be faced with a daunting task of trying to identify and footprint tens or hundreds of do- mains. Therefore, we prefer to automate as many tasks as possible via a combination of shell and expect scripts or perl programs.

In addition, there are many attackers well schooled in performing network reconnaissance activities without ever being discov- ered, and they are suitably equipped.

Thus, it is important to remember to minimize the amount and types of information leaked by your Internet presence and to implement vig- ilant monitoring. The pursuit of root access dates back to the early days of UNIX, so we need to provide some historical background on its evolution. UNIX was intended to be a powerful, ro- bust, multiuser operating system that excelled at running programs, specifically, small programs called tools.

The early UNIX environments were usually located inside Bell Labs or in a university setting where security was controlled primarily by physical means. Thus, any user who had physical access to a UNIX system was considered authorized.

In many cases, implement- ing root-level passwords was considered a hindrance and dismissed. Many ardent developers and code hackers scour source code for potential vulnerabilities.

Further- more, it is a badge of honor to post newly discovered vulnerabilities to security mailing lists such as Bugtraq. In this chapter, we will explore this fervor to determine how and why the coveted root access is obtained. Throughout this chapter, remember that in UNIX there are two levels of access: the all-powerful root and everything else.

There is no substitute for root! We even used the all-purpose netcat nc to grab banners that leak juicy infor- mation such as the applications and associated versions in use. In this chapter, we will explore the actual exploitation and related techniques of a UNIX system. It is important to remember that footprinting and network reconnaissance of UNIX systems must be done before any type of exploitation.

Footprinting must be executed in a thorough and me- thodical fashion to ensure that every possible piece of information is uncovered. Once we have this information, we need to make some educated guesses about the potential vul- nerabilities that may be present on the target system. This process is known as vulnerabil- ity mapping.

This is a critical phase in the actual exploitation of a target system that should not be overlooked. It is necessary for attackers to map attributes such as listening services, specific version numbers of running servers for example, Apache 1. Although this is tedious, it can provide a thorough analysis of potential vulnerabilities without actually exploiting the target system.

This will determine the existence of a real vulnerability with a high degree of certainty. On the freeware side, Nessus www. Needless to say, these attackers were inexpert and unsuccessful. Remote access is defined as gaining access via the network for example, a listening service or other communication channel. Local access attacks are also referred to as privilege escalation attacks. It is important to understand the relationship between remote and local access.

There is a logical progression where attackers remotely exploit a vulnerability in a listening service and then gain local shell access. Once shell access is obtained, the attack- ers are considered to be local on the system. We try to logically break out the types of at- tacks that are used to gain remote access and provide relevant examples.

Once remote access is obtained, we explain common ways attackers escalate their local privileges to root. Finally, we explain information-gathering techniques that allow attackers to garner information about the local system so that it can be used as a staging point for additional attacks.

Rather, we aim to cate- gorize these attacks and to explain the theory behind them. Thus, when a new attack is discovered, it will be easy to understand how it works, though it was not specifically cov- ered. The media would like everyone to believe that there is some sort of magic involved with compromising the security of a UNIX system.

In reality, there are three primary methods to remotely circumventing the security of a UNIX system: 1. Routing through a UNIX system that is providing security between two or more networks 3. How can you log in to the system if it is not running a service that allows interactive logins telnet, ftp, rlogin, or ssh? Are your systems vulnerable? Potentially, but attackers would have to exploit a listening service, wuftp, to gain access. It is imperative to remember that a service must be listening to gain access.

If a service is not listening, it cannot be broken into remotely. How is this possible? In many instances attackers circumvent UNIX firewalls by source routing packets through the firewall to internal systems. This feat is possible because the UNIX kernel had IP forwarding enabled when the firewall application should have been performing this function.

In most of these cases, the attackers never actually broke into the firewall per se; they simply used it as a router. Maybe not. What if you surf to www. This may allow evilhacker. Think of the implications of this if you were logged in with root privileges while web surfing. Throughout this section, we will address specific remote attacks that fall under one of the preceding three categories.

If you have any doubt about how a remote attack is possi- ble, just ask yourself three questions: 1. Is there a listening service involved? Does the system perform routing? You are likely to answer yes to at least one question. A brute force attack may not appear sexy, but it is one of the most effective ways for attackers to gain access to a UNIX system.

Services like finger, rusers, and sendmail were used to identify user accounts on a target system. Once attackers have a list of user accounts, they can begin trying to gain shell access to the target system by guessing the password associated with one of the IDs. Unfortunately, many user accounts have either a weak password or no password at all. Given enough users, most systems will have at least one Joe account.

To our amazement, we have seen thousands of Joe ac- counts over the course of performing our security reviews. Why are poorly chosen pass- words so common?

While it is entirely possible to guess passwords by hand, most passwords are guessed via an automated brute force utility. A one-time password mechanism would be most desirable. Some freeware utili- ties that will help make brute forcing harder are listed in Table In addition to these tools, it is important to implement good password management procedures and to use common sense. A data driven attack is executed by sending data to an active service that causes unintended or undesirable results.

Data driven attacks are categorized as either buffer overflow attacks or input validation attacks. Each attack is described in detail next. Buffer overflow attacks date as far back as and the infamous Robert Morris Worm incident; however, useful infor- mation about specific details of this attack was scant until This type of behavior is associ- ated with specific C functions like strcpy , strcat , and sprintf , among oth- ers.

A buffer overflow condition would normally cause a segmentation violation to occur. However, this type of behavior can be exploited to gain access to the target system. Al- though we are discussing remote buffer overflow attacks, buffer overflow conditions oc- cur via local programs as well and will be discussed in more detail later. We have a fixed-length buffer of bytes.

Recall from Chapter 3 that we used VRFY to help us identify potential users on the target system by trying to verify their email address. Let us also assume that sendmail is set user ID SUID to root and running with root privileges, which may or may not be true for every system. Stuffing 1, bytes into the VRFY buffer could cause a denial of service and crash the sendmail dae- mon; however, it is even more dangerous to have the target system execute code of your choosing.

This is exactly how a successful buffer overflow attack works. When the attack is executed, special assembly code known as the egg is sent to the VFRY command as part of the actual string used to overflow the buffer. When the VFRY buffer is overrun, attackers can set the return ad- dress of the offending function, allowing the attackers to alter the flow of the program.

Game over. It is imperative to remember that the assembly code is architecture and operating sys- tem dependent. Our example is very simplistic—it is extremely difficult to create a working egg. In addition, the friendly Teso folks have created some tools that will automatically generate shellcode.

Although it is impossible to design and code a program that is completely free of bugs, there are steps that help minimize buffer overflow conditions. Security is the last item to be addressed and falls by the wayside. Vendors border on being negligent with some of the code that has been released recently. Many vendors are well aware of such slipshod security coding practices, but do not take the time to address such issues.

Their approach is to immunize the programs at compile time to help minimize the impact of buffer overflow. Keep in mind that these mechanisms are not a silver bullet, and users should not be lulled into a false sense of security. This may slow down some programs, but tends to increase the security of each application. This includes bounds checking each variable, especially environment variables.

This includes minimizing the use of SUID root programs where possible. Even if a buffer overflow attack were executed, users would still have to escalate their privileges to root. Many times programmers are unaware of a potential buffer overflow condition; however, a third party can easily detect such defects.

The OpenBSD camp continually audits their source code and has fixed hundreds of buffer overflow conditions, not to mention many other types of security-related problems. Disable Unused or Dangerous Services We will continue to address this point throughout the chapter.

Disable unused or dangerous services if they are not essential to the opera- tion of the UNIX system. Not every service is capable of being wrapped. However, those that are will greatly enhance your security posture. In addition to wrap- ping each service, consider using kernel-level packet filtering that comes standard with most free UNIX operating systems for example, ipchains or netfilter for Linux and ipf for BSD. Disable Stack Execution Some purists may frown on disabling stack execution in favor of ensuring each program is buffer-overflow free.

It has few side effects, however, and pro- tects many systems from some canned exploits. In Linux there is a no-stack execution patch available for the 2.

For Solaris 2. This will prevent many Solaris-related buffer overflows from working. Although the SPARC and Intel application binary interface ABI mandate that the stack has exe- cute permission, most programs can function correctly with stack execution disabled. By default, stack execution is enabled in Solaris 2. Disabling stack execu- tion will normally log any program that tries to execute code on the stack and tends to thwart most script kiddies.

However, experienced attackers are quite capable of writing and distributing code that exploits a buffer overflow condition on a system with stack execution disabled. While people go out of their way to prevent stack-based buffer overflows by dis- abling stack execution, other dangers lie in poorly written code. Heap-based overflows are based on overrunning memory that has been dynamically allocated by an application.

This dif- fers from stack-based overflows, which depend on overflowing a fixed-length buffer. Thus, you should not become lulled into a false sense of security by just disabling stack execution. Al- though this attack is rather dated, it provides an excellent example of an input validation attack. To reiterate, if you understand how this attack works, your understanding can be applied to many other attacks of the same genre even thought it is an older attack.

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