Potential server crash exploit

Someone joined our server claiming he could crash it, I wasn't affected but everyone but me was kicked. Afterwards our server console gave this error, it seems he tried to connect/login to the server configuration manager. It may be nothing but I figured I'd show this just incase this is an actual exploit. We run a bukkit build however as mojang and bukkit work closely together I thought I'd share it here too.

03.11 21:58:53 [Server] INFO at net.minecraft.server.ThreadServerApplication.run(SourceFile:818)
03.11 21:58:53 [Server] INFO at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:419)
03.11 21:58:53 [Server] INFO at net.minecraft.server.MinecraftServer.q(MinecraftServer.java:486)
03.11 21:58:53 [Server] INFO at net.minecraft.server.DedicatedServer.r(DedicatedServer.java:215)
03.11 21:58:53 [Server] INFO at net.minecraft.server.MinecraftServer.r(MinecraftServer.java:569)
03.11 21:58:53 [Server] INFO at net.minecraft.server.DedicatedServerConnection.b(SourceFile:29)
03.11 21:58:53 [Server] INFO at net.minecraft.server.DedicatedServerConnectionThread.a(DedicatedServerConnectionThread.java:44)
03.11 21:58:53 [Server] INFO at net.minecraft.server.NetLoginHandler.c(NetLoginHandler.java:45)
03.11 21:58:53 [Server] INFO at net.minecraft.server.NetLoginHandler.d(NetLoginHandler.java:123)
03.11 21:58:53 [Server] INFO at net.minecraft.server.ServerConfigurationManagerAbstract.attemptLogin(ServerConfigurationManagerAbstract.java:238)
03.11 21:58:53 [Server] INFO java.lang.NullPointerException
03.11 21:58:53 [Server] WARNING Failed to handle packet: java.lang.NullPointerException