| Injection attacks, including SQL injection, cross-site scripting, and operating system command injection, rank the top two entries in the MITRE Common Vulnerability Enumeration (CVE). Under this attack model, an application (e.g., a web application) uses some untrusted input to produce an output program (e.g., a SQL query). Applications may be vulnerable to injection attacks because the untrusted input may alter the output program in malicious ways. Recent work has established a rigorous definition of injection attacks. Injections are benign iff they obey the NIE property, which states that injected symbols strictly insert or expand noncode tokens in the output program. Noncode symbols are strictly those that are either removed by the tokenizer (e.g., insignificant whitespace) or span closed values in the output program language, and code symbols are all other symbols. This thesis demonstrates that such attacks are possible on applications for Android---a mobile device operating system---and Bash---a common Linux shell---and shows by construction that these attacks can be detected precisely. Specifically, this thesis examines the recent Shellshock attacks on Bash and shows how it widely differs from ordinary attacks, but can still be precisely detected by instrumenting the output program's runtime. The paper closes with a discussion of the lessons learned from this study and how best to overcome the practical challenges to precisely preventing these attacks in practice. |
