"One font vulnerability to rule them all": "A story of cross-software ownage, shared codebases and advanced exploitation"

Presented at REcon 2015, June 21, 2015, 4 p.m. (60 minutes)

"Font rasterization software is clearly among the most desirable attack vectors of all time, due to multiple reasons: the wide variety of font file formats, their significant structural and logical complexity, typical programming language of choice (C/C++), average age of the code, ease of exploit delivery and internal scripting capabilities provided by the most commonly used formats (TrueType and OpenType). As every modern widespread browser, document viewer and operating system is exposed to processing external, potentially untrusted fonts, this area of security has a long history of research. As a result, nearly every major vendor releases font-related security advisories several times a year, yet we can still hear news about more 0-days floating in the wild.

Over the course of the last few months, we performed a detailed security audit of the implementation of OpenType font handling present in popular libraries, client-side applications and operating systems, which appears to have received much less attention in comparison to e.g. TrueType. During that time, we discovered a number of critical vulnerabilities, which could be used to achieve 100% reliable arbitrary code execution, bypassing all currently deployed exploit mitigations such as ASLR, DEP or SSP. More interestingly, a number of those vulnerabilities were found to be common across various products, enabling an attacker to create chains of exploits consisting of a very limited number of distinct security bugs.

In this presentation, we will outline the current state of the art with regards to font security research, followed by an in-depth analysis of the root cause and reliable exploitation process of a number of recently discovered vulnerabilities, including several full exploit chains. In particular, we will demonstrate how a universal PDF file could be crafted to fully compromise the security of a Windows 8.1 x86/x64 operating system via just a single vulnerability found in both Adobe Reader and the Adobe Type Manager Font Driver used by the Windows kernel."



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