An intrusion detection system is improved by altering its signatures and thresholds during a denial of service attack, in order to decrease the rate at which an intrusion detection sensor sends alerts to an intrusion detection server. A governor within the sensor is associated with each signature. The governor may include an alert log, a timer, an alert-generation-rate threshold, and rules that prescribe actions to be taken when the alert-generation-rate threshold is exceeded. The governor records the generation time of each alert by the sensor, and determines the rate at which the sensor is presently generating alerts. When the present alert-generation rate exceeds the alert-generation-rate threshold, the governor alters the associated signature threshold to decrease the alert generation rate of the intrusion detection sensor.

Limiting the output of alerts generated by an intrusion detection sensor during a denial of service attack

A method of operating an intrusion detection system. The system determines occurrence of a signature event indicative of a denial of service intrusion on a protected device. A value of a signature event counter is increased. The value of the signature event counter is adjusted to not include a count of signature events past a sliding window. The value of the signature event counter is determined to exceed a signature threshold quantity, followed by generation of an alert at a time subsequently recorded in a log. The log is cleared of entries past a permissible age. A present alert generation rate is determined as a ratio of the total number of timestamps in the log to the permissible age. The present alert generation rate is ascertained to exceed an alert generation rate threshold. A selected element of the signature set is altered to decrease the alert generation rate.

Method of operating an intrusion detection system

An intruder on a server is identified by providing files having attractive names in a subdirectory of the server. An agent is provided within one or more of the files. The agent is launched on an intruder's processor after the file containing the agent is downloaded. The agent locates various files and data on the intruder's processor and sends copies of the files and data to the server thus allowing a network administrator at the server to identify the intruder.

Identifying potential intruders on a server

This paper describes our technical approach to developing and delivering Unix host- and network-based security products to meet the increasing challenges in information security. Today`s global ``Infosphere`` presents us with a networked environment that knows no geographical, national, or temporal boundaries, and no ownership, laws, or identity cards. This seamless aggregation of computers, networks, databases, applications, and the like store, transmit, and process information. This information is now recognized as an asset to governments, corporations, and individuals alike. This information must be protected from misuse. The Security Profile Inspector (SPI) performs static analyses of Unix-based clients and servers to check on their security configuration. SPI`s broad range of security tests and flexible usage options support the needs of novice and expert system administrators alike. SPI`s use within the Department of Energy and Department of Defense has resulted in more secure systems, less vulnerable to hostile intentions. Host-based information protection techniques and tools must also be supported by network-based capabilities. Our experience shows that a weak link in a network of clients and servers presents itself sooner or later, and can be more readily identified by dynamic intrusion detection techniques and tools. The Network Intrusion Detector (NID) is one such tool. NID is designed to monitor and analyze activity on an Ethernet broadcast Local Area Network segment and produce transcripts of suspicious user connections. NID`s retrospective and real-time modes have proven invaluable to security officers faced with ongoing attacks to their systems and networks.

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Harry R. Bruestle

Papers

Verifying the secure setup of UNIX client/servers and detection of network intrusion