A Fuzzer for Detecting Use-After-Free Vulnerabilities

Fuzzing is an extensively used automated vulnerability detection technique. Most existing fuzzers are guided by edge coverage, which makes them less effective in detecting specific vulnerabilities, especially use-after-free (UAF) vulnerabilities. This is because the triggering of a UAF vulnerability must not only cover a specific memory operation but also satisfy a specific sequence of operations. In this paper, we propose UAF-Fuzzer for detecting UAFs, which consists of static analysis and fuzzing stages. In the static analysis stage, UAF-Fuzzer first uses target identification to determine the basic blocks that may cause UAFs as the target basic blocks; subsequently, it then instruments these target basic blocks. Subsequently, we propose a memory operation evaluation method to assess the complexity of memory operations. In the fuzzing stage, UAF-Fuzzer assigns energy to seeds using a memory evaluation operation and employs a novel seed selection algorithm to prioritize the execution of test cases that are likely to trigger UAF vulnerabilities. We designed and implemented a UAF-Fuzzer to improve the detection of UAFs and compared it with AFL, AFLFast, FairFuzz, MOPT, EcoFuzz, and TortoiseFuzz in terms of UAF vulnerability detection, crash detection, and path discovery. The results showed that UAF-Fuzzer is more effective in terms of detecting UAF vulnerabilities. We have also discovered three UAF vulnerabilities, submitted them to the software maintainer for fixing, and obtained CVE IDs.