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FixMeUp: Repairing Access-Control Bugs in Web Applications

Sooel Son, Kathryn S McKinley, and Vitaly Shmatikov

Abstract

Access-control policies in Web applications ensure that only authorized users can perform security-sensitive operations. These policies usually check user credentials before executing actions such as writing to the database or navigating to privileged pages. Typically, every Web application uses its own, hand-crafted program logic to enforce access control. Within a single application, this logic can vary between different user roles, e.g., administrator or regular user. Unfortunately, developers forget to include proper access-control checks, a lot.

This paper presents the design and implementation of FIXMEUP, a static analysis and transformation tool that finds access-control errors of omission and produces candidate repairs. FIXMEUP starts with a high-level specification that indicates the conditional statement of a correct access-control check and automatically computes an inter- procedural access-control template (ACT), which includes all program statements involved in this instance of access- control logic. The ACT serves as both a low-level policy specification and a program transformation template. FIXMEUP uses the ACT to find faulty access-control logic that misses some or all of these statements, inserts only the missing statements, and ensures that unintended dependences did not change the meaning of the access-control policy. FIXMEUP then presents the transformed program to the developer, who decides whether to accept the proposed repair. Our evaluation on ten real-world PHP applications shows that FIXMEUP is capable of finding subtle access-control bugs and performing semantically correct repairs.

Details

Publication typeInproceedings
Published inNetwork and Distributed System Security Symposium (NDSS)
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