Critical WFTPD buffer overflow vulnerability
From: axl rose (rdxaxl_at_hotmail.com)
To: email@example.com, firstname.lastname@example.org Date: Sat, 28 Feb 2004 21:52:33 +0000
Name of Advisory: Critical WFTPD buffer overflow vulnerability
Discoverer: axl (email@example.com)
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."
- 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.
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.
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 v126.96.36.199). 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
004034C7 PUSH EBX ; &dest 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().
See attached source code.
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- application/x-zip-compressed attachment: xp_wftpd.zip