Covert Channels in IPv6 Norka B. Lucena, Grzegorz Lewandowski, and Steve J. Chapin Syracuse University PET 2005, Cavtat, Croatia May 31 st, 2005

PET 2005 Lucena, Lewandowski, Chapin2 Outline IPv6 Overview Covert Channels Description Active Wardens Analysis Conclusions

PET 2005 Lucena, Lewandowski, Chapin3 IPv6 Overview Header structure has a fixed length: 40 bytes Header does not present five of the fields from IPv4: header length, identification, flags, fragment offset, and checksum A full implementation includes six headers: Hop-by-hop Options Routing Fragment Destination Options Authentication (AH) Encapsulating Security Payload (ESP)

PET 2005 Lucena, Lewandowski, Chapin4 Covert Channels Covert channel as a communication path that allows transferring information in a way that violates a security policy Concerned only with network storage channels Adversary model allows Alice and Bob to be or not be the same as the Sender and Receiver A specification-based analysis of 22 covert channels

PET 2005 Lucena, Lewandowski, Chapin5 IPv6 Header: Hop Limit Setting an initial hop limit value and modifying it appropriately in subsequent packets Version (4 bits) Version (4 bits) Traffic Class (1 byte) Traffic Class (1 byte) Flow Label (20 bits) Flow Label (20 bits) Payload Length (2 bytes) Payload Length (2 bytes) Next Header (1 byte) Next Header (1 byte) Hop Limit (1 byte) Hop Limit (1 byte) Source Address (16 bytes) Source Address (16 bytes) Destination Address (16 bytes) Destination Address (16 bytes) Hop Limit (1 byte)

PET 2005 Lucena, Lewandowski, Chapin6 IPv6 Header: Hop Limit Alice sets an initial value, h, for the hop limit h h -  0 h +  1 AliceBob Alice signals a 0 decreasing by  the hop count relatively to the previous packet Alice signals a 1 increasing the same value by  Bandwidth: Bandwidth: n packets, n – 1 bits

PET 2005 Lucena, Lewandowski, Chapin7 Hop-by-Hop Options Header: Jumbograms Using Jumbograms as means of covert communication in two ways: Modifying an existing jumbogram length to append covert data Converting a regular datagram into a jumbogram to fill in the extra bytes with hidden content Next Header (1 byte) Next Header (1 byte) Hop Limit (1 byte) Hop Limit (1 byte) Option Type (1 byte) Option Type (1 byte) Option Data Length (1 byte) Option Data Length (1 byte) Option Data (Variable length or specified in the Option Data length field) Option Data (Variable length or specified in the Option Data length field) Next Header (1 byte) Next Header (1 byte) Hop Limit (1 byte) Hop Limit (1 byte) Option Type = C2 (1 byte) Option Type = C2 (1 byte) Option Data Length = 4 (1 byte) Option Data Length = 4 (1 byte) Jumbo Payload Length (4 bytes) Jumbo Payload Length (4 bytes)

PET 2005 Lucena, Lewandowski, Chapin8 Hop-by-Hop Options Header: Jumbograms AliceBob Bandwidth: Bandwidth: Varies C Alice sets the payload length of the IPv6 header to 0 Alice sets the option type of the Hop-by-Hop header to C2 Alice sets the option data length of the Hop-by-Hop header to 4

PET 2005 Lucena, Lewandowski, Chapin9 Routing Header: Routing Type 0 Fabricating “addresses” out of arbitrary data meaningful only to the covert communicating agents Next Header (1 byte) Next Header (1 byte) Header Extension Length (1 byte) Header Extension Length (1 byte) Routing Type = 0 (1 byte) Routing Type = 0 (1 byte) Segment Left (1 byte) Segment Left (1 byte) Reserved (4 bytes) Reserved (4 bytes) Addresses (16 bytes each) Addresses (16 bytes each)

PET 2005 Lucena, Lewandowski, Chapin10 Routing Header: Routing Type 0 AliceBob Bandwidth: Bandwidth: Up to 2048 bytes/per packet Alice takes inserts two fake addresses into the routing header Alice modifies the header extension length field accordingly Alice does not modify the original value of the segments left field … … … … … …

PET 2005 Lucena, Lewandowski, Chapin11 Active Wardens Stateless Active Warden Knows the protocol syntax and semantics and attempts to verify them “Sees” one packet at a time Performs at two levels of diligence Stateful Active Warden Registers already-observed semantic conditions Network-aware Active Warden Is a stateful active warden Is also a network topologist

PET 2005 Lucena, Lewandowski, Chapin12 Conclusions Provide awareness of the existence of at least 22 covert channels in IPv6 Generate discussion toward harmful means of covert communication Help to understand potential attacks that exploit IPv6 traffic to take appropriate countermeasures Raise issues for considerations by implementors of IPv6 protocol stacks and firewalls Introduce three types of active wardens: stateless, stateful, and network-aware

PET 2005 Lucena, Lewandowski, Chapin13 Any Questions?

PET 2005 Lucena, Lewandowski, Chapin14 Thank You All!