Security Implications of Windows Access Tokens

A white paper has been published by Luke Jennings of MWR InfoSecurity which discusses the security exposures that can occur due to the manner in which access tokens are implemented in the Microsoft® Windows Operating System.

A brief overview of the intended function, design and implementation of Windows access tokens is given, followed by a discussion of the relevant security consequences of their design. More specific technical details are then given on how the features of Windows access tokens can be used to perform powerful post-exploitation functions during penetration testing, along with a basic methodology for including an assessment of the vulnerabilities exposed through tokens in a standard penetration test.

Discussion is also included about why many corporate environments (assessed during penetration tests conducted by MWR InfoSecurity) have been found to not be operating in a manner which limits the risk of such issues. Finally, best practice advice is given on how to defend against these attacks.

It must be noted that the security issues discussed in this white paper do not represent a flaw in the Microsoft® Windows Operating System but are an expected consequence based on the design and implementation of Windows access tokens. The important point is that many corporate environments do not account for these issues within their security strategy and, consequently, the controls in many of these environments are not sufficient to withstand the techniques discussed here.

Additionally, it is acknowledged that the security implications of Windows access tokens have been discussed before both in general terms and to different degrees of technical detail. This document is not intended to present such discussions as being fundamentally new; instead it is intended to collate some of the existing knowledge, introduce some new findings and to demonstrate why many years after the general principles discussed were highlighted, many corporate environments are still vulnerable to these issues.

The paper is based upon research originally presented by the author at Defcon 15 and Chaos Computer Congress (CCC) 2007.