Vulnerability Note VU#279763

RhinoSoft Serv-U remote administration client transmits password in plaintext

Overview

A vulnerability exists in the remote administration client for RhinoSoft Serv-U. During the authentication process, the client ignores the S/KEY one-time password (OTP) challenge sent by the server and sends the password entered by the user in plaintext.

I. Description

RhinoSoft Serv-U is a shareware Windows FTP server that supports S/KEY one-time password (OTP) authentication using MD4 or MD5 hash algorithms. Cat Soft LLC is also involved in the development of Serv-U and is an affiliate of RhinoSoft. The Serv-U distribution includes an administration client that can be used to manage Serv-U servers remotely. Serv-U user accounts can be configured to use plaintext or S/KEY OTP authentication, and accounts can be granted several levels of administrative privilege on the server. When a user with administrative privileges attempts to log on to a Serv-U server using the remote administration client, and that user's account is configured on the server to use S/KEY OTP authentication, the server correctly sends an S/KEY OTP challenge, but the administration client ignores the challenge and sends the password entered by the user in plaintext. The server refuses the plaintext password and authentication fails, and the plaintext password is exposed on the network.

See RFC 1760 and RFC 2289 for more information on S/KEY and one-time password (OTP) authentication.

II. Impact

A properly located intruder using a sniffer can obtain administrative users' passwords. In addition, an administrative user account configured to use S/KEY OTP cannot log into a Serv-U server using a vulnerable remote administration client.

III. Solution

The CERT/CC is currently unaware of a practical solution to this problem.

IIIb. Workarounds

It may be possible to use other forms of encryption, such as a VPN, SSH, or IPsec, to secure a remote administration connection to a Serv-U server.

Systems Affected

Vendor	Status	Date Notified	Date Updated
RhinoSoft	Vulnerable	19-Nov-2001

References

http://www.rhinosoft.com/
http://www.serv-u.com/
http://www.cat-soft.com/
http://www.ietf.org/rfc/rfc1760.txt
http://www.ietf.org/rfc/rfc2289.txt
http://www.iss.net/security_center/static/7925.php
http://securitytracker.com/alerts/2001/Dec/1002882.html

Credit

The CERT Coordination Center thanks Fred Maxwell for reporting this vulnerability.

This document was written by Art Manion.

Other Information

Date Public:	2001-11-19
Date First Published:	2001-11-19
Date Last Updated:	2002-11-15
CERT Advisory:
CVE-ID(s):
NVD-ID(s):
US-CERT Technical Alerts:
Metric:	4.74
Document Revision:	25

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