Sun Solaris telnet authentication bypass vulnerability

Overview

A vulnerability in the Sun Solaris telnet daemon (in.telnetd) could allow a remote attacker to log on to the system with elevated privileges.

Description

The Sun Solaris telnet daemon may accept authentication information via the USER environment variable. However, the daemon does not properly sanitize this information before passing it to the login program, and login makes unsafe assumptions about the information. This may allow a remote attacker to trivially bypass the telnet and login authentication mechanisms. In some default configurations of Solaris this vulnerability cannot be exploited to gain access to the root account, but it can be used to gain privileges of other accounts, such as adm and lp.

According to Sun, Solaris 10 (SunOS 5.10) and Solaris “Nevada” (SunOS 5.11) are affected by this issue. More information is available in Sun Alert Notification 102802 and in Alan Hargreaves’ blog, here and here.

This vulnerability is being exploited by a worm, for more information see the Security Sun Alert Feed and Technical Alert TA07-059A.

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Impact

A remote attacker could log on to a vulnerable system via telnet and gain elevated privileges.

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Solution

Apply a patch
Apply the patches referenced in Sun Alert Notification 102802.

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Disable telnet

Disable telnet if it’s not needed. Telnet can be disabled by issuing the following command:

# svcadm disable telnetRestrict access

You may wish to block access to the vulnerable software from outside your network perimeter, specifically by blocking access to the ports used by Sun Solaris telnet (typically 23/tcp). This will limit your exposure to attacks.

Prefer SSH over telnet

SSH provides a comparatively more secure method for remotely logging into a system than telnet. As general advice, we recommend using SSH rather than telnet.

Vendor Information

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Sun Microsystems, Inc. __ Affected

Notified: February 12, 2007 Updated: February 16, 2007

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

Please see Sun Alert Notification 102802.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%23881872 Feedback>).

CVSS Metrics

Group	Score	Vector
Base	0	AV:–/AC:–/Au:–/C:–/I:–/A:–
Temporal	0	E:ND/RL:ND/RC:ND
Environmental	0	CDP:ND/TD:ND/CR:ND/IR:ND/AR:ND

References

• <http://www.ietf.org/rfc/rfc1572.txt&gt;
• <http://blogs.sun.com/tpenta/entry/the_in_telnetd_vulnerability_exploit&gt;
• <http://blogs.sun.com/tpenta/entry/more_on_the_in_telnetd&gt;
• <http://sunsolve.sun.com/search/document.do?assetkey=1-26-102802-1&gt;
• <http://blogs.sun.com/security/entry/solaris_in_telnetd_worm_seen&gt;
• <http://secunia.com/advisories/24166/&gt;
• <http://securitytracker.com/alerts/2007/Feb/1017625.html&gt;
• <http://www.ciac.org/ciac/bulletins/r-139.shtml&gt;
• <http://riosec.com/solaris-telnet-0-day&gt;
• <http://www.computerdefense.org/?p=258&gt;
• <http://blog.ncircle.com/blogs/vert/archives/2007/02/whats_old_is_new_again.html&gt;
• <http://erratasec.blogspot.com/2007/02/trivial-remote-solaris-0day-disable.html&gt;
• <http://www.com-winner.com/0day_was_the_case_that_they_gave_me.pdf&gt;
• <http://asert.arbornetworks.com/2007/02/solaris-telnet-scanning-possible-worm/&gt;

Acknowledgements

This vulnerability was reported by Kingcope.

This document was written by Art Manion and Chris Taschner.

Other Information

CVE IDs:	CVE-2007-0882
Severity Metric:	67.50 Date Public: