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CERT(sm) Summary CS-96.04
July 23, 1996

The CERT Coordination Center periodically issues the CERT Summary to
draw attention to the types of attacks currently being reported to our
Incident Response Team. The summary includes pointers to sources of
information for dealing with the problems. We also list new or updated
files that are available for anonymous FTP from
     ftp://info.cert.org/pub/

Past CERT Summaries are available from
     ftp://info.cert.org/pub/cert_summaries/
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Increasing Sophistication of Intruder Community Expertise
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In earlier summaries, we noted that the intruder community was
analyzing operating system source code to develop increasingly
sophisticated and effective exploitation techniques. The intruder
community is now developing new techniques to analyze programs for
potential vulnerabilities even in the absence of source code. This can
be done with a tool that traces system calls and subroutine calls
within a program, thus allowing a person to match such calls against
command line parameters.

Although there is little that sites can do in direct response to this
information, it does highlight the importance of staying up to date
with security patches and workarounds for your operating systems and
applications.


Operating System Concerns
- -------------------------

We receive reports relating to incident activity from many different
sites using a wide variety of operating systems. Because of problems
we see that directly relate to operating systems, we felt it
worthwhile to make a few observations about choosing an operating
system. For information on this subject, see

  ftp://info.cert.org/pub/tech_tips/choose_operating_sys


Forged Advisories
- -----------------

Occasionally, we see forged advisories on various newsgroups or other
distribution lists. If you have the Pretty Good Privacy (PGP) program,
you can determine whether or not an advisory is genuine by checking
the PGP signature.

We use PGP to sign all our advisories. To verify that a CERT advisory
is authentic,

  1. Get the CERT public key from

       ftp://info.cert.org/pub/CERT_PGP.key

  2. Verify the authenticity of the document by checking the PGP
     signature. To do this, enter the following command:

       %pgp <filename>

     You should see a message that includes the statement

       Good signature from user "CERT Coordination Center <cert@cert.org>".
       Signature made <date>



Recent Activity and Trends
- --------------------------

Since the May CERT Summary, we have seen these continuing trends in
incidents reported to us.

1. Linux root compromises

At least once a week we see reports of Linux machines that suffer
break-ins leading to root compromises. In many of these incidents, the
systems were misconfigured, and/or the intruders exploited well-known
vulnerabilities (for which CERT advisories have been published); the
intruders then installed Trojan horse programs and/or network
monitoring programs (packet sniffers).

If you are running Linux, we strongly urge you to keep up to date with
patches and security workarounds. We recommend that you also review

  ftp://info.cert.org/pub/cert_advisories/CA-94:01.network.monitoring.attacks
  ftp://info.cert.org/pub/cert_advisories/CA-94:01.README

Further, you may want to monitor the Linux newsgroups and mailing
lists for security patches and workarounds. More information can be
found at

  http://bach.cis.temple.edu/linux/linux-security/


2. Telnetd in Linux systems

We have noticed an increase in the exploitation of a vulnerability in
the telnetd environment on unpatched Linux-based systems. If you have
not patched your system(s) for this vulnerability, we urge you to
review CERT advisory CA-95:14 and the associated README file and
install the patch or workaround provided.

  ftp://info.cert.org/pub/cert_advisories/CA-95:14.Telnetd_Environment_Vulnerability
  ftp://info.cert.org/pub/cert_advisories/CA-95:14.README


3. Password Cracking

We continue to receive daily reports of unauthorized site access as a
result of compromised accounts and/or "cracked" passwords. For
information about protecting your password files, please see

  ftp://info.cert.org/pub/tech_tips/passwd_file_protection


4. Sendmail attacks

Although discussed in previous summaries, we continue to receive
reports each week about intruders who attempt to exploit sendmail
vulnerabilities. We have published several advisories on sendmail. If
you have not addressed the vulnerabilities in sendmail, we urge you to
review these advisories and take appropriate action. All advisories,
including sendmail advisories, can be found at

  ftp://info.cert.org/pub/cert_advisories/

In many of these attempts, intruders are trying to obtain
password files. For information on protecting your password files, see

  ftp://info.cert.org/pub/tech_tips/passwd_file_protection

We have had many questions about when to use the sendmail restricted
shell program (smrsh). You should run smrsh with any UNIX system that
is running sendmail, regardless of vendor or version.

smrsh is now included as part of the current sendmail distribution
(effective with version 8.7.1). We strongly urge you to upgrade to the
latest version of sendmail. See

  ftp://info.cert.org/pub/latest_sw_versions/sendmail


5. cgi-bin vulnerabilities

Since our last summary, we've seen an increase in the number of
reports relating to vulnerabilities in cgi-bin programs. Any cgi-bin
program that relies on escape_shell_cmd() to prevent exploitation of
shell-based library calls may be vulnerable to attack. For more
information about cgi-bin vulnerabilities and patches, please see

  ftp://info.cert.org/pub/cert_advisories/CA-96.06.cgi_example_code
  ftp://info.cert.org/pub/cert_advisories/CA-96.06.README

There have been discussions in several public forums about the problem
of general-purpose interpreters being placed in the cgi-bin directory.
If these interpreters are accessible in the cgi-bin directory of a Web
server, then a remote user can execute any command the interpreters
can execute on that server. For more details and patch information,
see

  ftp://info.cert.org/pub/cert_advisories/CA-96.11.interpreters_in_cgi_bin_dir


6. Mail spamming/spoofing attacks

We receive at least three incidents each week of mail spamming and/or
spoofing attacks. For information on responding to and recovering from such
activity, see

  ftp://info.cert.org/pub/tech_tips/email_bombing_spamming
  ftp://info.cert.org/pub/tech_tips/email_spoofing



What's New in the CERT FTP Archive
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We have made the following changes since the last CERT Summary (May 22, 1996).


* New Additions

ftp://info.cert.org/pub/cert_advisories/

    CA-96.10.nis+_configuration
    CA-96.10.README
    CA-96.11.interpreters_in_cgi_bin_dir
    CA-96.11.README
    CA-96.12.suidperl_vul
    CA-96.12.README
    CA-96.13.dip_vul
    CA-96.13.README

ftp://info.cert.org/pub/cert_bulletins/

    VB-96.08.sgi
    VB-96.09.freebsd
    VB-96.10.sco
    VB-96.11.freebsd

ftp://info.cert.org/pub/tech_tips/

    choose_operating_sys                Things to consider when choosing an
                                        operating system for your site

ftp://info.cert.org/pub/tools/

    ifstatus                            Added the ifstatus program

ftp://info.cert.org/pub/vendors/

    sun/sun_bulletin_00135              Added bulletin from Sun
                                        Microsystems, Inc.

    dec/dec-96.0383                     Added bulletin from Digital
                                        Equipment Corporation



* Updated Files

ftp://info.cert.org/pub/cert_advisories/

    CA-95:13.README                     Added vendor information for Digital
                                        Equipment Corporation and Silicon
                                        Graphics, Inc.
                        
    CA-96.04.README                     Added information about the next
                                        release of BIND

    CA-96.08.README                     Added vendor information for Digital
                                        Equipment Corporation, NEC
                                        Corporation, and Data Design Systems,
                                        Inc. Added patch information for
                                        FreeBSD, Inc.

    CA-96.09.README                     Added vendor information for Digital
                                        Equipment Corporation. Added pointers
                                        to Silicon Graphics, Inc. release notes
                                        and Sun Microsystems, Inc. patches

    CA-96.12.README                     Added vendor information for FreeBSD,
                                        NEC Corporation, and Digital Equipment
                                        Corporation

ftp://info.cert.org/pub/FIRST/

    first-contacts                      Updated contact information


ftp://info.cert.org/pub/latest_sw_versions/

    bind                                Added pointer to version 4.9.4
    ifstatus                            Added pointer to ifstatus

If you use any of the software listed in this directory, we recommend
that you upgrade to the current versions. Among other changes, these
new versions address security weaknesses present in previous versions.

If you have any questions about the software listed in this directory,
please contact the vendor for more information.


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How to Contact the CERT Coordination Center

Email    cert@cert.org

Phone    +1 412-268-7090 (24-hour hotline)
                CERT personnel answer 8:30-5:00 p.m. EST
                (GMT-5)/EDT(GMT-4), and are on call for
                emergencies during other hours.

Fax      +1 412-268-6989

Postal address
        CERT Coordination Center
        Software Engineering Institute
        Carnegie Mellon University
        Pittsburgh PA 15213-3890
        USA

To be added to our mailing list for CERT advisories and bulletins, send your
email address to
        cert-advisory-request@cert.org

CERT advisories and bulletins are posted on the USENET news group
         comp.security.announce

CERT publications, information about FIRST representatives, and other
security-related information are available for anonymous FTP from
        http://www.cert.org/
        ftp://info.cert.org/pub/

If you wish to send sensitive incident or vulnerability information to CERT
staff by electronic mail, we strongly advise you to encrypt your message.
We can support a shared DES key or PGP. Contact the CERT staff for more
information.

Location of CERT PGP key
         ftp://info.cert.org/pub/CERT_PGP.key

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Copyright 1996 Carnegie Mellon University
This material may be reproduced and distributed without permission provided
it is used for noncommercial purposes and credit is given to the CERT
Coordination Center.

CERT is a service mark of Carnegie Mellon University.

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