CVE-2018-18920
Py-EVM v0.2.0-alpha.33 allows attackers to make a vm.execute_bytecode call that triggers computation._stack.values with ‘"stack": [100, 100, 0]’ where b’x’ was expected, resulting in an execution failure because of an invalid opcode. This is reportedly related to "smart contracts can be executed indefinitely without gas being paid."
Source: CVE-2018-18920