A vulnerability in the handling of the NEW-ENVIRON command allows a malicious telnet server to gain information from a client's environment variables.
The Telnet network protocol is described in RFC854 and RFC855 as a general, bi-directional communications facility. The Telnet protocol is commonly used for command-line login sessions between Internet hosts.
The vulnerability is in the NEW-ENVIRON sub-command that is the mechanism to used for passing environment information between a telnet client and server. Use of this mechanism enables a telnet user to propagate configuration information to a remote host when connecting. Please see RFC1572 for more information. As specified in section 3 of RFC1572 the expected default behavior should be "that there will not be any exchange of environment information".
An attacker may be able to gather information about remote systems and users who connect to attackers malicious telnet server. An attacker would have to trick a victim into initiating a telnet connection using a vulnerable client. This may be accomplished with an HTML rendered email or web page, using the TELNET:// URI handler, however further user interaction may be required.
Apply an update from your vendor
Patches, updates, and fixes should be available from multiple vendors.
Gaël Delalleau is credited with this discovery. Thank you to iDefense for coordinating the release of information about this issue.
This document was written by Robert Mead based on information in the iDEFENSE Security Advisory
|Date First Published:||2005-06-14|
|Date Last Updated:||2005-07-28 21:05 UTC|