CVE-2022-21685 Integer underflow in Frontier

Frontier is Substrate's Ethereum compatibility layer. Prior to commit number 8a93fdc6c9f4eb1d2f2a11b7ff1d12d70bf5a664, a bug in Frontier's MODEXP precompile implementation can cause an integer underflow in certain conditions. This will cause a node crash for debug builds. For release builds and...