Name of Advisory: Critical WFTPD buffer overflow vulnerability Severity: Critical Discoverer: axl (rdxaxl@hotmail.com) Released: Today Vendor Notified: Today WFTPD who? what? when? ~~~~~~~~~~~~~~~~~~~~~~ Vendor quote: "WFTPD Server has been a leading FTP server for Windows since it was released in 1993. Its stability and security have long been relied on by technology companies, educational institutions, government departments, individuals and others, to provide a secure FTP site." Tested versions ~~~~~~~~~~~~~~~ - WFTPD Pro Server 3.21 Release 1 (trial) (latest version) - WFTPD Pro Server 3.20 Release 2 (trial) - WFTPD Server 3.21 Release 1 (trial) (latest version) - WFTPD Server 3.10 Release 1 (trial) All tested versions are vulnerable. Other versions may also be vulnerable. Overview ~~~~~~~~ There's a stack based buffer overflow vulnerability that a remote attacker can exploit to execute arbitrary code on the remote system running the vulnerable WFTPD server software. For WFTPD Pro Server, the code will execute as SYSTEM, and for WFTPD Server, the code will execute as the user who started the server. Vulnerability details ~~~~~~~~~~~~~~~~~~~~~ The vulnerable FTP commands are LIST, NLST, and STAT. The user must be logged in as any user unless the Secure option in the registry is 0. There's special code to check if the first argument's first character is equal to '-'. If it is, and there's a ' ' character at some later position, we'll execute this vulnerable code (WFTPD Pro trial v3.21.1.1). For the programming challenged people, I've added comments: 004034B8 MOV EAX,[EBP+8] ; strchr(userbuf, ' ') 004034BB SUB EAX,ESI 004034BD DEC EAX ; num bytes to copy 004034BE CMP EAX,EDI ; (below) jump if num bytes to copy 004034C0 JLE SHORT 004034C4 ; is <= max_len - 2 004034C2 MOV EDI,EAX 004034C4 PUSH EDI ; max(max_len - 2, num bytes to copy) 004034C5 INC ESI ; don't copy '-' 004034C6 PUSH ESI ; &userbuf[1] 004034C7 PUSH EBX ; &dest[1] on the stack 004034C8 CALL memcpy Anything between the first '-' char to the first ' ' char can be copied to the string. This string only has room for 31 characters and a terminating null byte. Obviously, the programmer mistakenly used max() instead of min(). Exploit ~~~~~~~ See attached source code. _________________________________________________________________ Store more e-mails with MSN Hotmail Extra Storage – 4 plans to choose from! http://click.atdmt.com/AVE/go/onm00200362ave/direct/01/