The present invention relates generally to the field of computer security in packet based communications networks such as Internet Protocol (IP) networks, and in particular to a method and apparatus for defending against Denial of Service (DoS) attacks in such networks wherein the target victim itself recognizes the presence of such an attack, identifies the source of the attack, and requests control of the routing of malicious packets by its associated carrier network.
Each day, many thousands of new "zombies" join the pool of hijacked PCs (Personal Computers) sending spam to e-mail users and launching Denial of Service (DoS) attacks against e-commerce sites, government resources, and other network infrastructure. In fact, it has been estimated that as many as 170,000 zombie machines are added to the Internet daily. Denial of service (DoS) attacks in particular can cause major service disruptions when limited resources need to be allocated to the attackers instead of to legitimate uses. Such attacks have been estimated to have resulted in over $26,000,000 of losses in calendar year 2004. The attacking machines are usually compromised zombie machines controlled by remote masters, and typically inflict damage by sending vast numbers of IP (Internet Protocol) packets across the Internet directed to the target victim of the attack. The culprits who instigate such attacks range from teenagers aiming to take down small business to international criminal organizations attempting to extort money from large corporations.
Presently, there are two commonly used approaches for defending against such Denial of Service attacks - one which is largely manual and one which is automated. The first approach requires manual identification of the existence of an attack by the end user (i.e., the target victim), followed by a manual (e.g., telephone) report of the attack to the victim's service provider (i.e., carrier), combined with a request that the carrier identify the source of the reported attack and instigate a protective barrier to prevent packets which are part of the attack from getting through the network to the victim. Most typically, such an approach will result in the carrier identifying the source of the offending packets, followed by its refusal to accept any packets from that source (or at least any packets from that source which are destined for the particular attack victim which identified and reported the existence of the attack).
A second approach for defending against such Denial of Service attacks provides a more automated process which requires the service provider to include sophisticated "packet washer" or "scrubber" filters through which each and every packet destined for the end user to be protected must pass. That is, changes are made to the Internet routing tables so that all of the given end user's traffic is routed through such a filter, which examines each packet in turn in an attempt to decide whether the packet is malicious or not. If it does not appear to be malicious, it is forwarded on to the end user, but if it does appear to be malicious, it is filtered out and discarded.
Each of these approaches however have significant limitations. The first approach requires substantial manual intervention and often may not be capable of addressing the problem of an attack until significant damage has already been done. And the second approach is unable to leverage application analysis of packets, since often, only the target is able to extract, and thus analyze, the data contents of the packet. (For example, if cryptographic protocols are used, it is typically only the ultimate destination of the packet that is capable of decoding the encoded packet data.) Moreover, a leveraged attack on a victim's application may not be based only on excessive bandwidth, but rather, may result from certain types of functional requests. Thus, a solution to the problem of Denial of Service attacks is needed wherein the attacks are promptly recognized, identified, and (preferably without manual intervention) stopped.
We have recognized that while the best place to recognize the existence of a Denial of Service attack is at the target victim (who has the ultimate motivation to identify and address attacks on itself), the best place to defend against the attack is within the network (i.e., in the carrier's network). As such, in accordance with the principles of the present invention, the benefits of each of the two aforementioned prior art approaches may be advantageously realized without the corresponding disadvantages. In particular, the present invention provides a method for defending against a Denial of Service attack wherein a target victim of an attack recognizes the existence of an attack, identifies the source of the attack, and automatically instructs its carrier network to limit transmission of packets from the identified source to the target victim.
More specifically, the present invention provides a method and apparatus for defending against Denial of Service attacks by a target victim which is provided service by an Internet Protocol (IP) based carrier network, according to claim 1.
In accordance with an illustrative embodiment of the present invention, a Zombie Attack Processor (hereinafter, "Zapper") provides a new type of security device that allows the victim of a Denial of Service attack to "push back" by denouncing attackers to its carrier, which will, in response, update a table of source/destination IP address pairs which are to be blocked. More specifically, upon recognizing that an attack is taking place, the victim will identify one or more pairs of source and destination IP addresses which are specified in packets deemed to be a part of the attack, and communicate those IP address pairs to its carrier for blocking.
Note that, in accordance with certain illustrative embodiments of the present invention, the attacker (i.e., the identified source IP address or addresses) need not be cut off completely from the network, but rather may be prohibited only from sending packets to the victim (i.e., the identified destination IP address or addresses). This may be advantageous, particular in the case where the identified source IP address or addresses represent a legitimate user which has been taken over (i.e., a zombie) for the given attack against the victim. Thus, the owner of the taken over machine may continue to use the system for legitimate purposes, while the attack being perpetrated on the victim (unbeknownst to the legitimate user) is nonetheless advantageously thwarted. Moreover, note that the technique in accordance with such illustrative embodiments of the present invention also advantageously provides protection from overly zealous identification of attackers by a given victim. Since, in accordance with the principles of the present invention, the identification of an attack is left to the discretion of the apparent victim, it is clearly advantageous that only traffic to the given victim is being cut off or restricted.
Advantageously, the denunciation protocol could include security signatures so that the Zapper infrastructure itself could not be used to launch a Denial of Service attack. Moreover, the protocol might advantageously make use of redundant connections to the carrier network, as well as redundant UDP (User Datagram Protocol), to ensure delivery even under congested network conditions. (UDP is an IP communications protocol which is fully familiar to those of ordinary skill in the art.) Advances in network processors and memories enable such a defense to be scaled to potentially large numbers of attackers - far beyond the capacity of earlier routers - advantageously without requiring manual intervention by either the victim or the carrier and hence capable of an extremely timely response.
In accordance with various illustrative embodiments of the present invention, such a Zapper filtering engine may be implemented as either a stand-alone box included in the carrier network, or, alternatively, as a line card incorporated into otherwise conventional network elements which are already present in the network. Moreover, in accordance with certain illustrative embodiments of the present invention, the Zapper filter may be advantageously deployed by the carrier within the network at a location relatively close to the attack origins, or it may be initially placed to advantageously defend premium customers from attack.
In accordance with various illustrative embodiments of the present invention, IP address pair entries to be blocked may either time out (i.e., be automatically removed after a predetermined elapsed period of time), or, alternatively, may be cleared by explicitly issued reprieves. In this manner, the network will advantageously return to a clean state without the need for the use of garbage collection algorithms. Illustratively, denouncers (i.e., customers of the carrier network who are enabled to identify and protect against attacks) may, for example, be given a limited number of "chits" (source/destination IP address pairs to be entered and blocked) - say, for example, on the order of a hundred thousand - which may, for example, be based proportionally on the amount of business that the given customer does with the given service provider (i.e., carrier).
Moreover, in accordance with certain illustrative embodiments of the present invention, network diagnosis may be advantageously provided by having the illustrative Zapper return an ICMP (Internet Control Message Protocol, fully familiar to those of ordinary skill in the art) unreachable message with, for example, some predetermined probability whenever a packet is dropped as having been identified as comprising a blocked source/destination IP address pair. Such an error return may, in accordance with one illustrative embodiment of the present invention, include a code which will enable the sender of the blocked packet to query a database for details regarding who placed the blocking request on such packets and, possibly, the reasons for such a request.
And, in accordance with certain illustrative embodiments of the present invention, supplementary tools might be advantageously provided as well. For example, such tools might include Internet server plug-ins for recognition of leveraged Denial of Service attacks, links to various IDS systems (Intrusion Detection Systems), databases for network diagnosis (see discussion above), and methods for providing guidance for placement of Zapper functionality within a given carrier's infrastructure. Illustrative embodiments of the present invention which provide various ones of these supplementary tools will be obvious to those skilled in the art in light of the disclosure herein.
Note that the operation of the Zapper filtering mechanism according to certain illustrative embodiments of the present invention is similar to that of a conventional firewall, except that it operates based on a potentially large number (e.g., millions) of very simple rules. In particular, the Zapper rules may be expressed in the form "if the source IP address of a given packet is a.b.c.d and the destination IP address of the packet is w.x.y.z, then block (i.e., drop) the packet."
And in accordance with other illustrative embodiments of the present invention, rather than prohibiting the transmission of packets with a given source and destination IP address, the Zapper filter may de-prioritize such packets. That is, the filtering mechanism may either assign such packets a low routing priority or enforce a packet rate limit on such packets. In either case, packets with the given source and destination IP addresses will be unable to have a significant effect on traffic and thus will no longer result in a successful Denial of Service attack on the victim.
In accordance with various illustrative embodiments of the present invention, attack detection may be advantageously recognized by the victim by algorithms of varying degrees of simplicity or sophistication, many of which will be obvious to those skilled in the art. For example, in accordance with one illustrative embodiment of the invention, application logs may be examined and an attack may be identified based solely on the presence of very high traffic levels (e.g., high packet rates) from either a single identified source or a plurality of identified sources. (Note that this is one conventional method of identifying the presence of a Denial of Service attack and will be familiar to those of ordinary skill in the art.)
In accordance with another illustrative embodiment of the invention, however, application based analysis of packet contents may be performed to identify packets or sequences of packets having a suspicious nature, such as, for example, recognizing that there have been frequent database searches for non-existent database elements; recognizing that there have been multiple requests apparently from a human being which occur at a higher rate than a person could initiate them; identifying syntactically invalid requests; and identifying suspicious amounts of traffic at particularly sensitive times in the operation of a normally occurring activity. (An example of the latter class of suspicious packets might be identified, for example, if a stock trading web site notices particularly disruptive traffic at a sensitive time during an imminent stock transaction.) And in accordance with other illustrative embodiments of the invention, a number of different indicia of a possible attack, which may include, for example, one or more of the above described situations, may be advantageously combined in a more sophisticated analysis to identify the presence of an attack.
Carrier network 13, the network carrier which provides service to target victim 11, receives IP packets from various sources and transmits them to target victim 11. As is shown in the figure, the IP packets being transmitted to the victim are, in fact, associated with a Denial of Service attack thereon, and are being sent by a large number of zombie machines 14. Carrier network 13 also includes zapper 15, which advantageously defends against Denial of Service attacks in accordance with an illustrative embodiment of the present invention.
More specifically, in operation and in accordance with the illustrative embodiment of the present invention, attack detector 12, upon determining that a Denial of Service attack is being perpetrated on target victim 11, transmits one or more source/destination IP address pairs to zapper 15, which causes carrier network 13 to limit (e.g., block) the transmission of IP packets whose source IP address and destination IP address match those of any of the transmitted source/destination IP address pairs, thereby limiting (or eliminating) the Denial of Service attack from zombies 14 to attack victim 11. Note that attack detector 12 advantageously transmits the source/destination IP address pairs with use of redundant connection 17. Note also that IP packets transmitted from zombies 14 to unrelated servers 16 are advantageously not affected.
It should be noted that all of the preceding discussion merely illustrates the general principles of the invention. It will be appreciated that those skilled in the art will be able to devise various other arrangements, which, although not explicitly described or shown herein, embody the principles of the invention, and are included within its scope. For example, although the present invention has been described specifically with respect to Internet Protocol (IP) networks, it will be obvious to those of ordinary skill in the art that the particular communications protocol used is not relevant to the principles of the present invention, and, therefore, the present invention can be used in an identical manner in the context of any data packet based network in which packets having source and destination addresses associated therewith are transmitted through the network.
In addition, all examples and conditional language recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. It is also intended that such equivalents include both currently known equivalents as well as equivalents developed in the future - i.e., any elements developed that perform the same function, regardless of structure.
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.