Abstract:
A security system for a computer network that has a plurality of devices connected thereto comprises a security subsystem, a master system and a secure link. The security subsystem is connected to at least some of the devices in the network. The security subsystem is configured to monitor activities of the at least some devices on the network and detect attacks on the at least some devices. The master system monitors the integrity of the security subsystem and registers information pertaining to attacks detected by the security subsystem. The secure link is connected between the security subsystem and the master system. The master system monitors the integrity of the security subsystem and receives the information pertaining to the attacks through the secure link.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a continuation of co-pending U.S. application Ser. No. 09/770,525 filed Jan 25, 2001, the entire disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates to a method and apparatus for verifying the integrity of a computer security subsystem for preventing attacks on computer network security systems.  
         [0004]     2. Background  
         [0005]     Concurrent with the rise in connectivity among diverse computer networks and the corresponding increase in dependence on networked information systems, there has been a dramatic increase in the need for robust security to enforce restrictions on access to and prevent intrusion on secure systems. The topology of the interconnected networks has also grown increasingly complex, and often involves open networks such as the internet that expose secure systems to increased threats of attack. Consequently, no single solution has yet been proposed that addresses all current needs for intrusion detection and response. Instead, a vast assortment of security devices and techniques has evolved and has generally been implemented differently on individual systems. This has resulted in a global security patchwork, inherently susceptible to attack and to individual systems which themselves implement a hodge podge of different security devices and techniques.  
         [0006]     Attempts to gain unauthorized access to computer networks capitalize on inherent loopholes in a network&#39;s security topology. It is known, for example, that although a secure system connected to the internet may include firewalls and intrusion detection systems to prevent unauthorized access, weaknesses in individual security components are often sought out and successfully exploited. The rapid introduction of new technology exacerbates the problem, creating or exposing additional weaknesses that may not become known until a breach in security has already occurred.  
         [0007]     A fundamental weakness shared in common by current intrusion detection and response systems is their “flat” or non-hierarchical implementation. The configuration shown in  FIG. 1  is an example of such a typical network implementation on a hypothetical “target network”. The network  10  includes a plurality of file servers  14 , workstations  16 , a network intrusion detection system (IDS)  18 , a remote access server  20  and a web server  22 . These devices are connected to each other over network backbone  12 , and form a local or wide-area network (LAN or WAN). Router  26  is connected directly to an open network such as the internet,  30 , and is connected to the devices on network backbone  12  through network firewall  24 .  
         [0008]     The firewall  24  and the IDS  18  are part of the security system of network  10 . Firewall  24  is configurable and serves to control access by hosts on the internet to resources on the network. This protects network  10  from intruders outside the firewall, essentially by filtering them out. IDS  18  scans packets of information transmitted over backbone  12  and is configured to detect specific kinds of transactions that indicate that an intruder is attempting, or already has gained access to the network,  10 . In this way, the IDS protects the network from intruders inside as well as outside the firewall. Other devices on network  10  may also contribute to network security, such as remote access server  20  which permits access directly to network  10  from remote computers (not shown), for example over a modem. Remote access server  20  must also implement some security function such as username and password verification to prevent intruders from gaining access to the network and bypassing firewall  24 .  
         [0009]     In a typical intrusion scenario on a target network connected to the internet, an intruder will first learn as much as possible about the target network from available public information. At this stage, the intruder may do a “whois” lookup, or research DNS tables or public web sites associated with the target. Then, the intruder will engage in a variety of common techniques to scan for information. The intruder may do a “ping” sweep in order to see which machines on the target network are running, or they may employ various scanning utilities well known in the art such as “rcpinfo”, “showmount” or “snmpwalk” to uncover more detailed information about the target network&#39;s topology. At this stage the intruder has done no harm to the system, but a correctly configured network IDS should be able, depending on its vantage point on the network, to detect and report surveillance techniques of intruders that follow known patterns of suspicious activity. These static definitions, known as “intrusion signatures”, are effective only when the intruder takes an action or series of actions that closely follow the established definitions of suspicious activity. Consequently, if the IDS is not updated, is disabled or encounters an unknown or new method of attack, it will not respond properly. However, if steps are not taken at this point in the attack to prevent further penetration into the target network, the intruder may actually begin to invade the network, exploiting any security weaknesses (such as the IDS that may not have reacted earlier to the intruder), and securing a foothold on the network. Once entrenched, the intruder may be able to modify or disable any device belonging to the target network including any remaining IDS or firewall.  
         [0010]     Methods used by intruders to gain unauthorized access to computer networks evolve in sophistication in lock step with advances in security technology. It is a typical, however that successful attacks on network systems often begin by attacking the security subsystems in place on the target network that are responsible for detecting common intrusion signatures, disabling those systems and destroying evidence of the intrusion.  
         [0011]     U.S. Pat No. 5,916,644 (Kurtzberg et al.) discloses a method for testing the integrity of security subsystems wherein a specially configured system connected to directly a target computer network will systematically test security on the network by simulating attacks on security devices in order to verify that they are operational. Specifically, the disclosed method randomly simulates an attack on the network. If the attack is detected, the security subsystems are assumed to be functioning. If not, they are considered compromised, and an attack may already be underway. This method is an improvement over passive systems that do not check themselves and therefore cannot properly report on their own status when they have been disabled.  
         [0012]     A major shortcoming of this approach is that these security systems reside on the same networks that they seek to protect and are similarly vulnerable to attack once an intruder has gotten a foothold on the network. In other words, they are not themselves immune to the attacks of intruders. As a result each advance in the prior art is just another new security hurdle on the network to be defeated. In this light, the active scanning approach disclosed in Kurtzberg is not fundamentally different from any other security measure (such as a firewall) in that it is non-hierarchical and depends completely on the vigilance of a human network manager.  
         [0013]     Therefore, there exists a need for a self-diagnosing network security system that can protect a target network from both internal and external intruders and that is resistant to attacks perpetrated on the system it has been deployed to protect. Furthermore, there is a need for an active security system that will take measured action against perceived security threats even in the absence of a human network manager.  
       BRIEF SUMMARY OF THE INVENTION  
       [0014]     It is therefore an object of the present invention to provide a network security system for a network of computers that is capable of solving the above mentioned problems in the prior art.  
         [0015]     It is another object of the present invention to provide a network security system that has a component that can directly monitor multiple network security devices on a network for attack signatures and other suspicious network activity suggesting an attempt to compromise security on that network.  
         [0016]     It is another object of the present invention to provide a network security system that can dynamically detect new patterns or trends in network activity that suggest an attempt to compromise network security on a single network or on a plurality of otherwise unrelated networks.  
         [0017]     It is another object of the present invention to provide a network security system that can resist intrusion during an attack on the network.  
         [0018]     It is another object of the present invention to provide a security system providing integrity verification for security devices on a network, and can also reliably verify its own integrity.  
         [0019]     It is another object of the present invention to provide a security system for a computer network that can take corrective measures after an attack has been detected to prevent an intruder from gaining further access to the network.  
         [0020]     It is another object of the present invention to provide a security system satisfying the above objectives for individual computers connected to an open network.  
         [0021]     According to an example of the present invention, there is provided a network security system to prevent intrusion on a target network having at least one security subsystem local to the target network provided to monitor network traffic and to detect attacks by an intruder on the system. The subsystem is connected via a secure link to a master system that is not otherwise connected to the target system. The master system monitors the subsystem via the secure link and registers information pertaining to the status of the subsystem. If the subsystem detects an attack on the target network, or does not respond to the master system, the master system will take appropriate action, ranging from logging the incident or notifying a network manager to attempting to shut down the network. Accordingly, even attacks that completely disable the subsystem will not prevent the master system from responding as long as the link remains secure.  
         [0022]     According to another example of the present invention, a multi-level hierarchy is implemented making the subsystem subordinate to the master system. In this configuration, commands can only be passed from the master system to the subsystem, ensuring that the integrity of the master system can not be undermined, even by successful attacks on the target network, or on the subsystem itself. Therefore, even a subversion of the subsystem and a compromised link between it and the master system is insufficient to disable the master system.  
         [0023]     According to another example of the present invention, a pseudo-attack generator associated with the master system is provided that simulates attacks on the target network that should be detected by the subsystem. By comparing the pseudo-attacks made on the target network to the attacks actually detected by the subsystem, the master system can determine whether the integrity of the subsystem has been compromised. Similarly, the subsystem may generate its own pseudo-attacks on other network security components to establish their integrity as well. Therefore it is possible to test comprehensively every security-related device connected to the target network.  
         [0024]     In another example of the present invention, the subsystem, and the master system acting through the subsystem, can implement corrective measures to mitigate or thwart suspected intruder attacks on the target network. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  is a block diagram showing the overall structure of an example of a network system according to the prior art.  
         [0026]      FIG. 2  is a block diagram showing an example of a network incorporating the system of the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]     The preferred embodiments of a network security system according to the present invention will hereinafter be described with reference to the accompanying drawings.  
         [0028]     Referring to  FIG. 2 , a first embodiment of the present invention is shown. Target network  100  is shown having the same basic components as the network of the prior art shown in  FIG. 1  with the addition of security subsystem  50 , however it should be noted that the actual configuration of the target network is not critical with the exception of at least one security subsystem  50 . Each of the security subsystem  50 , servers  14 , workstations  16 , IDS  18 , remote access server  20 , web server  22 , firewall  24  and router  26  are connected together over network backbone  12 . Each of the devices carry out communication over the backbone in accordance with a predetermined communication protocol such as Transmission Control Protocol/Internet Protocol (TCP/IP).  
         [0029]     Target network  100  is connected through firewall  24  and router  26  to the internet  30  as well as through remote access server  20  which may also be selectively connected to the internet  30  through remote user  21 . These two potential points of contact with an open network, in this case the internet, exposes target network  100  to the threat of intrusion from any host with access to the internet such as internet user  31 . In addition to threats from the outside, those with direct access to the resources of target network  100 , such as those using one of the workstations  16 , also pose an intrusion threat. If an intruder were to gain access to one of the critical security-related devices such as the IDS  18  or the firewall  24  or any trusted computer from within or outside the target network  100 , security on the network could be compromised.  
         [0030]     In the present invention, security subsystem  50  is connected to network backbone  12  and linked to each of the network&#39;s devices by a secure link  52 . Such a secure link may be established through an encrypted communication protocol such as Secure Sockets Layer (SSL). This ensures that communication between the security subsystem  50  and the other components of the target network cannot be intercepted by an intruder. A similar secure link  54  is established as a virtual private network (VPN) tunnel between the security subsystem  50  and a master system  60  connected to a remote network  110 . Although the remote network is shown having its own firewalls  62 , servers  66 , and router  68 , the ultimate configuration of remote network  110  is not critical beyond secure link  54  connecting security subsystem  50  and master system  60 . However, secure links  55  may be established between a device such as a network scanner  63  and a router  26  or remote user  21  on network  100 . Secure link  54  ensures that communication between the two networks cannot be intercepted by an intruder. Therefore, there should be no other direct connection between target network  100  and remote network  110  except over a secure link.  
         [0031]     Preferably, the security system defined herein is embedded as a software package and implemented on computers comprising at least a master system and the security subsystem.  
         [0032]     During operation, security subsystem  50  monitors the activities of the devices of the target network  100 . Particularly, the critical security-related functions of IDS  18  and firewall  24  are tested. The particular method employed by security subsystem  50  in testing these devices is not critical, however the above mentioned approach employing simulated attacks on the components would be suitable.  
         [0033]     Upon testing the devices, if the integrity of a device on target network  100  cannot be verified, security subsystem  50  reacts. For example, if IDS  18  has been identified by the subsystem as not reacting properly to attacks on it originating from the internet, appropriate countermeasures could include cutting off or restricting access to the network at firewall  24  or stop at application level. If instead, the firewall is determined not to be functioning, appropriate action might include disabling access to any servers  14  holding sensitive data. In one possible configuration of the present invention, security subsystem  50  reports network device status to master system  60  which processes the information, and decides on further action. In an alternate configuration, security subsystem  50  is responsible for implementing countermeasures directly. In both cases, however, the results of every test are passed to master system  60  where they are stored for analysis.  
         [0034]     The system of the present invention can also help thwart ongoing attacks and is uniquely suited to do so. In another preferred embodiment of the present invention, master system  60  hierarchically supercedes security subsystem  50 . As such, the activities of security subsystem  50  are defined as a child process of master system  60  and are subordinate thereto. Although information preferably flows both ways between master system  60  and security subsystem  50  in this embodiment, the master system in this embodiment does not take direction from the subsystem.  
         [0035]     As noted in the discussion of the prior art, non-hierarchical security systems are connected directly to a target network and are inherently susceptible to attacks on that network. This is in contrast to the present embodiment wherein, even if completely subverted during an attack on target system  100 , security subsystem  50  would not result in a takeover of master system  60 . The benefit of this configuration is that the master system would still be able to carry out its function. For example, if master system  60  is configured to sound an alarm when security subsystem  50  no longer responds to it, there would be no way, in this embodiment, for intruders on target network  100  to remotely shut down master system  60  because the master system will not respond to any instructions issued from a subordinate system. Although master system  60  may lose control of the target network, it is not in danger of being taken over by it. Additionally, if the link  54  between master system  60  and security subsystem  50  is severed or compromised, instructions may be routable instead through secure links  55 .  
         [0036]     In yet another embodiment of the present invention, remote network  110  is connected through router  70  to an open network such as the Internet. This enables master system  60  to send random pseudo-attacks to target network  100 . The pseudo-attacks may mimic any of the actual attack signatures known by the master system to be detectable by the target network. If the expected reply is not received by the master system, an early indication of an intruder attack on the target network is indicated.  
         [0037]     As set forth hereinabove, according to the present invention, it is possible to provide a method and apparatus for verifying the integrity of computers and computer networks that is independent of the network or computer being tested. In addition, by detecting early signs of intruder activity on a network, the present invention increases the likelihood that intruder attacks can be thwarted before they succeed.  
         [0038]     When implemented on an individual computer, such as a single workstation  16  connected to an open network such as internet  30 , the present invention functions similarly to prevent attacks on that computer originating from the open network. In the absence of network backbone  12  the functions of security subsystem  50  may be directly incorporated into an individual computer such as by software or peripheral hardware.  
         [0039]     When implemented across a plurality of otherwise unrelated target networks, the present invention functions to prevent attacks according to the methods described herein on each target network individually. The advantage of this configuration is that security information may be coordinated across several networks without connecting the networks together.  
         [0040]     Many different embodiments of the present invention may be constructed without departing from the spirit and scope of the invention. It should be understood that the present invention is not limited to the specific embodiments described in this specification. To the contrary, the present invention is intended to cover various modifications and equivalent arrangements included within the spirit and the scope of the claims.