Cisco Technology, Inc.

Michael L Hall, Jr

Nicholas Leavy

Gerald S Lathem

Kevin L Wiley

Mohit Yashpal Jaggi

Timothy Hahn

Systems detect maliciously formed TCP/IP retransmit packets attempting to pass through an intrusion detection system (IDS) and prevent them from reaching their destination by forcing early flow termination. As each packet arrives in the IDS, the TTL field is monotonically decreased by setting it to the smallest TTL received from the packet flow. Any packet flow that attempts to confuse the sensor with a low TTL will be starved off and will never reach the destination host. Each flow may be periodically reset to a high value or to the current packet value to allow flow recovery. In another embodiment, the TTL decrease mechanism may operate on a contingent basis, determined by the presence or absence of the flow identifier on a pre-determined list of flows that should never be restricted.

Use of per-flow monotonically decreasing TTLs to prevent IDS circumvention

Embodiments of the invention are directed to systems that detect maliciously formed TCP/IP retransmit packets attempting to pass through an intrusion detection system (IDS) and prevent them from reaching their destination by forcing early flow termination. The IDS may be configured to track a hash of certain fields in each packet. This set of hashes is maintained for all of the packets in the currently open TCP window for each flow. If the hash of a retransmit packet does not match the cached hash of the corresponding original packet, the system concludes that there is an attack under way and terminates the flow. The hash function may range in complexity and security from low complexity and relative insecurity to high complexity and high security. Hash algorithms may also be used in conjunction with a private seed value concatenated with the packet fields prior to hashing.

Use of packet hashes to prevent TCP retransmit overwrite attacks

A method and system for maintaining network activity data for intrusion detection includes storing data representative of network activity in datasets. The datasets include root datasets each having a root keyset and child datasets each having a child keyset with a key combination derived from and less granular than a root keyset. Child datasets are identified through their root datasets.

Growing community of inventors

Austin, TX, United States of America

Michael L Hall, Jr