// back

SSLTelnet Remote Format String Vulnerability

07.08.04

BACKGROUND

SSLtelnetd is a replacement for telnetd available as part of the FreeBSD
ports collection at http://www.freebsd.org/ports/security.html. It
implements the telnet protocol over SSL.

DESCRIPTION

SSLtelnet contains a format string vulnerability that could allow remote
code execution. 

The problem specifically exists within telnetd.c, on line 530 where an
argument deficient call is made to syslog(). The following snippet
reveals the vulnerable code:

SSL_set_verify(ssl_con,ssl_verify_flag,NULL);

    if (SSL_accept(ssl_con) <= 0) {
        static char errbuf[1024];

        sprintf(errbuf,"SSL_accept error %sn",
        ERR_error_string(ERR_get_error(),NULL));

        syslog(LOG_WARNING, errbuf);  // vulnerable call

        BIO_printf(bio_err,errbuf);

        /* go to sleep to make sure we are noticed */
        sleep(10);
        SSL_free(ssl_con);

        _exit(1);
    } else {
        ssl_active_flag=1;
    }

ANALYSIS

This vulnerability could be remotely exploitable under certain
conditions. If exploitation is successful, gaining root access is
possible as the process runs as root.

DETECTION

iDEFENSE has confirmed the existence of this vulnerability against
the current release, SSLTelnet version 0.13-1.

WORKAROUND

This project does not appear to be actively maintained and has now been
marked FORBIDDEN and DEPRECATED. End users should consider implementing
an alternate telnet/SSL solution.

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2004-0640 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org), which standardizes names for
security problems.

DISCLOSURE TIMELINE

04/03/2003    Vulnerability acquired by iDEFENSE
06/29/2004    Initial vendor contact
07/02/2004    Secondary vendor contact
07/08/2004    Public disclosure

CREDIT

 b0f is credited with this discovery.

Get paid for vulnerability research
http://www.idefense.com/poi/teams/vcp.jsp

LEGAL NOTICES

Copyright © 2004 Verisign, Inc.

Permission is granted for the redistribution of this alert
electronically. It may not be edited in any way without the express
written consent of iDEFENSE. If you wish to reprint the whole or any
part of this alert in any other medium other than electronically, please
email customerservice@idefense.com for permission.

Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
There are no warranties with regard to this information. Neither the
author nor the publisher accepts any liability for any direct, indirect,
or consequential loss or damage arising from use of, or reliance on,
this information.