Hiding TCP Traffic: Threats and Counter-measures

Hiding TCP Traffic: Threats and Counter-measures

Paper in proceedings outside WoS and Scopus

Computer networks were designed to be simple and routers do not validate the integrity of the processed traffic.
Consequently, an attacker can modify his or her traffic with the aim of confusing any analyser that intercepts the
traffic, e.g. monitoring and security software or lawful interception. This paper studies the attack that is based on
sending additional colliding TCP segments with the same sequential number but different content. The segments
with the correct message are delivered to the other communicating party of the TCP connection while the fake
segments are dropped en route. The goal of the fake segments is to confuse analysers into decoding a different
message to the one that is received by the other communicating party. The other communicating party does not
need to be aware of the attack and therefore does not need any specific software. Although this paper discuss the
advantages and disadvantages of the attack for an attacker, our ultimate goal was to find counter-measures
against the attack. Our contribution can be divided into four following parts. 1) We converted the attack to IPv6
and searched for possibilities that may force a middle box to drop fake packets. 2) We developed a tool called
LDP, which behaves as a TCP proxy server that masks outbound TCP traffic of a whole network. 3) We
identified several counter-measures. In addition, we implemented LNC, a tool that identifies the attack in pcap
files and removes the fake segments. Since LNC is a stand-alone tool, it also deals with traces generated by other
software than LDP as long as it is based on the same attack vector. 4) LDP and LNC were tested in both
laboratory environment and on the Internet. The experiments validated that the attack is applicable for a
communication with a server that is not under the control of an attacker. Several parameters of the attack were
evaluated during the experiments; mainly the number and the length of fake packets and their influence on the
performance of the attack and counter-measures.

Computer networks were designed to be simple and routers do not validate the integrity of the processed traffic.
Consequently, an attacker can modify his or her traffic with the aim of confusing any analyser that intercepts the
traffic, e.g. monitoring and security software or lawful interception. This paper studies the attack that is based on
sending additional colliding TCP segments with the same sequential number but different content. The segments
with the correct message are delivered to the other communicating party of the TCP connection while the fake
segments are dropped en route. The goal of the fake segments is to confuse analysers into decoding a different
message to the one that is received by the other communicating party. The other communicating party does not
need to be aware of the attack and therefore does not need any specific software. Although this paper discuss the
advantages and disadvantages of the attack for an attacker, our ultimate goal was to find counter-measures
against the attack. Our contribution can be divided into four following parts. 1) We converted the attack to IPv6
and searched for possibilities that may force a middle box to drop fake packets. 2) We developed a tool called
LDP, which behaves as a TCP proxy server that masks outbound TCP traffic of a whole network. 3) We
identified several counter-measures. In addition, we implemented LNC, a tool that identifies the attack in pcap
files and removes the fake segments. Since LNC is a stand-alone tool, it also deals with traces generated by other
software than LDP as long as it is based on the same attack vector. 4) LDP and LNC were tested in both
laboratory environment and on the Internet. The experiments validated that the attack is applicable for a
communication with a server that is not under the control of an attacker. Several parameters of the attack were
evaluated during the experiments; mainly the number and the length of fake packets and their influence on the
performance of the attack and counter-measures.

Law Interception, data hiding, TCP, covert channels.

Law Interception, data hiding, TCP, covert channels.

POLČÁK, L.; HRANICKÝ, R.; MATOUŠEK, P.

2014

22.05.2013

University of Defence in Brno

Brno

978-80-7231-922-0

Security and Protection of Information 2013, Proceedings of the Conference

83

96

14

https://www.fit.vut.cz/research/publication/10333/

article