SSLTelnet Remote Format String Vulnerability

iDEFENSE Security Advisory 07.08.04:

*I. 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.

*II. 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 %s\n",
        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;
    }

*III. 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.

*IV. DETECTION*

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

*V. 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.

*VI. 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 <http://cve.mitre.org/>), which
standardizes names for
security problems.

*VII. 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

*VIII. CREDIT*

 b0f is credited with this discovery.

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

*IX. LEGAL NOTICES*

Copyright (c) 2004 iDEFENSE, Inc.

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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.
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