Harm-DoS: Hash Algorithm Replacement for Mitigating Denial-of-Service Vulnerabilities in Binary Executables.

Programs and services relying on weak hash algorithms as part of their hash table implementations are vulnerable to hash-collision denial-of-service attacks. In the context of such an attack, the attacker sends a series of program inputs leading to hash collisions. In the best case, this slows down the execution and processing for all requests, and in the worst case it renders the program or service unavailable. We propose a new binary program analysis approach to automatically detect weak hash functions and patch vulnerable binary programs, by replacing the weak hash function with a secure alternative. To verify that our mitigation strategy does not break program functionality, we design and leverage multiple stages of static analysis and symbolic execution, which demonstrate that the patched code performs equivalently to the original code, but does not suffer from the same vulnerability. We analyze 105,831 real-world programs and confirm the use of 796 weak hash functions in the same number of programs. We successfully replace 759 of these in a non-disruptive manner. The entire process is automated. Among the real-world programs analyzed, we discovered, disclosed and mitigated a zero-day hash-collision vulnerability in Reddit.