telnet and rlogin URLs disclose sensitive information, including Environment variables

Overview

Some telnet clients may disclose sensitive information in environment variables

Description

Web browsers can be configured to respond to certian protocol types through the use of a helper application. In this case, web browsers can respond to telnet: URLs with the use of a helper application. RFC 1572 (<http://andrew2.andrew.cmu.edu/rfc/rfc1572.html&gt;) permits telnet servers to request environment variables of telnet clients prior to authentication. Quoting from that document:

Once the two hosts have exchanged a WILL and a DO, the sender of the DO NEW-ENVIRON is free to request that environment variables be sent. Only the sender of the DO may send requests (IAC SB NEW-ENVIRON SEND IAC SE) and only the sender of the WILL may transmit actual environment information (via the IAC SB NEW-ENVIRON IS … IAC SE command). Though this option may be used at any time throughout the life of the telnet connection, the exchange of environment information will usually happen at the startup of the connection. This is because many operating systems only have mechanisms for propagating environment information at process creation, so the information is needed before the user logs in.

Thus, if a telnet server requests environment variables from a telnet client that implements RFC 1572, that client will send the environment variables prior to authentication. The CERT/CC is aware of a proof-of-concept implementation of such a server.

Further, web browsers will often use help applications to deal with non-web protocols such as telnet. If a web browser is configured to use a RFC-1572-compliant telnet client as a telnet helper, then a telnet: URL can be used to obtain sensitive information from that web browser, including such environment variables as USER, HOME, PGPPASS, SSH_CLIENT and other information commonly stored in the environment. At least one Windows telnet client, UWIN, implements RFC 1572, as well as some unix telnet clients. At the present time, we have not developed an exhaustive list of clients that implement RFC 1572.

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Impact

A client machine can be “tricked” into revealing sensitive information stored in environment variables.

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Solution

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Vendor Information

22404

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Caldera __ Affected

Notified: May 23, 2000 Updated: September 26, 2000

Status

Affected

Vendor Statement

After looking into the source code for Linux’s netkit-telnet (version 0.16), I believe that it’s not vulnerable to the PGPPASS problem. The client code that handles the ENVIRON option works okay if the server sends an empty list of variables (which means the client will send all “exported” environment variables), but fails miserably when a list of variable names is given. The code totally ignores ENV_VAR (which normally marks the start of a new env name), and when it comes across ENV_VALUE it will try to grok the variable name but stomps all over it with NUL bytes :-)

So, to make a long story short, you can’t use netkit-telnet to extract arbitrary variables from the user’s environment. You can however retrieve exported variables. Unless the user does funny things in his .telnetrc file, the only variables exported should be USER, TERM and DISPLAY.

So the damage that can be done with telnet: URLs is roughly the same as with rlogin: URLs. This does divulge some information, but only little more than an ident query would.

My conclusion is that there’s no urgent need to modify the rlogin and telnet clients in any way. In the long haul, browser vendors should probably rethink which URLs are allowed under which circumstances, and whether they require user confirmation (much like netscape’s “you’re about to enter a secure site”).

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%2322404 Feedback>).

U/WIN __ Affected

Notified: November 13, 2000 Updated: November 13, 2000

Status

Affected

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

CERT/CC has received credible third-party information suggesting that the U/WIN telnet client is vulnerable to this problem.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%2322404 Feedback>).

Microsoft __ Not Affected

Notified: May 23, 2000 Updated: September 26, 2000

Status

Not Affected

Vendor Statement

We checked our Telnet clients and we are okay for Windows NT4 and Windows 2000.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%2322404 Feedback>).

Apple Unknown

Notified: May 23, 2000 Updated: September 26, 2000

Status

Unknown

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%2322404 Feedback>).

BSDI Unknown

Notified: May 23, 2000 Updated: September 26, 2000

Status

Unknown

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%2322404 Feedback>).

Compaq Computer Corporation Unknown

Notified: May 23, 2000 Updated: September 26, 2000

Status

Unknown

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%2322404 Feedback>).

Data General Unknown

Notified: May 23, 2000 Updated: September 26, 2000

Status

Unknown

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%2322404 Feedback>).

FreeBSD Unknown

Notified: May 23, 2000 Updated: September 26, 2000

Status

Unknown

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%2322404 Feedback>).

Fujitsu Unknown

Notified: May 23, 2000 Updated: September 26, 2000

Status

Unknown

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%2322404 Feedback>).

Hewlett Packard Unknown

Notified: May 23, 2000 Updated: September 26, 2000

Status

Unknown

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%2322404 Feedback>).

IBM Unknown

Notified: May 23, 2000 Updated: September 26, 2000

Status

Unknown

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%2322404 Feedback>).

NCR Unknown

Notified: May 23, 2000 Updated: September 26, 2000

Status

Unknown

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%2322404 Feedback>).

NEC Unknown

Notified: May 23, 2000 Updated: September 26, 2000

Status

Unknown

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%2322404 Feedback>).

NetBSD Unknown

Notified: May 23, 2000 Updated: September 26, 2000

Status

Unknown

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%2322404 Feedback>).

OpenBSD Unknown

Notified: May 23, 2000 Updated: September 26, 2000

Status

Unknown

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%2322404 Feedback>).

RedHat Unknown

Notified: May 23, 2000 Updated: September 26, 2000

Status

Unknown

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%2322404 Feedback>).

SCO Unknown

Notified: May 23, 2000 Updated: September 26, 2000

Status

Unknown

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%2322404 Feedback>).

SGI Unknown

Notified: May 23, 2000 Updated: September 26, 2000

Status

Unknown

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%2322404 Feedback>).

Sequent Unknown

Notified: May 23, 2000 Updated: September 26, 2000

Status

Unknown

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%2322404 Feedback>).

Siemens Nixdorf Unknown

Notified: May 23, 2000 Updated: September 26, 2000

Status

Unknown

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%2322404 Feedback>).

Sony Unknown

Notified: May 23, 2000 Updated: September 26, 2000

Status

Unknown

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%2322404 Feedback>).

Sun Unknown

Notified: May 23, 2000 Updated: September 26, 2000

Status

Unknown

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%2322404 Feedback>).

Unisys Unknown

Notified: May 23, 2000 Updated: September 26, 2000

Status

Unknown

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%2322404 Feedback>).

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CVSS Metrics

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References

<http://andrew2.andrew.cmu.edu/rfc/rfc1572.html&gt;

Acknowledgements

Thanks to Steve Bellovin of AT&T, who reported this problem to us.

This document was written by Shawn V Hernan.

Other Information

CVE IDs:	CVE-2000-0892
Severity Metric:	1.01 Date Public: