Frontier is Substrate’s Ethereum compatibility layer. A security issue was discovered affecting parsing of the RPC result of the exit reason in case of EVM reversion. In release build, this would cause the exit reason being incorrectly parsed and returned by RPC. In debug build, this would cause an overflow panic. No action is needed unless you have a bridge node that needs to distinguish different reversion exit reasons and you used RPC for this. There are currently no known workarounds.