25C3 -

25th Chaos Communication Congress
Nothing to hide

Fabian Yamaguchi
Day Day 2 (2008-12-28)
Room Saal 3
Start time 17:15
Duration 01:00
ID 2909
Event type lecture
Track Hacking
Language used for presentation en

TCP Denial of Service Vulnerabilities

Accepting the Partial Disclosure Challenge

The Transmission Control Protocol (TCP) is one of the fundamental protocols used in today's communication networks. Recently, there has been an increased discussion on possible Denial of Service attacks against TCP-based services, which has largely been triggered by the partial disclosure of several vulnerabilities by the security company Outpost24. This talk will present several TCP vulnerabilities in an attempt to find out just what they found.

This year, vulnerabilities have been identified in the specifications of various core network protocols. This included BGP, DNS and TCP. Accompanying these wide-ranging discoveries, a new form of vulnerability disclosure named "partial disclosure" has been introduced. In practice, this means that the public knows that there is something wrong, yet, it is uninformed about the details. This, of course, can be understood as a challenge to find out just what could be wrong, which is what we at Recurity Labs did after the Denial of Service vulnerabilities in TCP had been announced.

This talk will present known vulnerabilities in the protocol, which have been receiving rather sparse media-attention, as well as some attacks we have been working on during our research. Additionally, we hope to provide sufficient background information on the protocol's fundamental weaknesses to motivate further research on the subject. We argue that certain assumptions made by the protocol engineers almost 30 years ago do not hold in today's networks and that most possible Denial of Service attacks against TCP can be derived from these assumptions.