[UNIX] SSLTelnet Daemon Remote Format String Vulnerability

From: SecuriTeam (support_at_securiteam.com)
Date: 07/11/04

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Date: 11 Jul 2004 12:01:56 +0200

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      SSLTelnet Daemon Remote Format String Vulnerability
    ------------------------------------------------------------------------

    SUMMARY

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

    A format string vulnerability exists in SSLTelnet when input is passed to
    a logging function without proper handling. This could lead to remote code
    execution.

    DETAILS

    Vulnerable Systems:
     * SSLTelnet version 0.13-1

    CVE Information:
     <http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2004-0640>
    CAN-2004-0640

    The vulnerable piece of code is located in telnetd.c, line 530:
    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;
        }

    It can be seen that there is a call to syslog() without proper input
    validation. The issue can be exploited remotely under certain conditions
    and would allow remote code execution, usually with root privileges.

    Disclosure Timeline
    06/29/2004 Initial vendor contact
    07/02/2004 Secondary vendor contact
    07/08/2004 Public disclosure

    ADDITIONAL INFORMATION

    The information has been provided by
    <mailto:idlabs-advisories@idefense.com> iDefense Security.
    The original article can be found at:
    <http://idefense.com/application/poi/display?id=114&type=vulnerabilities&flashstatus=true> http://idefense.com/application/poi/display?id=114&type=vulnerabilities&flashstatus=true

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