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TUCoPS :: Unix :: General :: ciacg009.txt

Sendmail Unix Vulnerability



                       The U.S. Department of Energy
                    Computer Incident Advisory Capability
                           ___  __ __    _     ___
                          /       |     /_\   /
                          \___  __|__  /   \  \___

                             INFORMATION BULLETIN

                          Unix sendmail vulnerability

February 12, 1996 23:00 GMT                                        Number G-09b
PROBLEM:       Sendmail (prior to Sendmail 8.6.10) contains a vulnerability 
               which allows local and remote users to execute privileged 
PLATFORM:      All versions of "sendmail" prior to Version 8.6.10, including 
               Sendmail 5.67+IDA-1.5 and most vendor versions.
DAMAGE:        Local and remote users can gain privileged access.
SOLUTION:      Install vendor patches if possible or implement sendmail 
ASSESSMENT:    This vulnerability is being actively exploited on the Internet.

Bulletin G-09a supersedes CIAC's Bulletin G-09 dated January 31, 1996.
G-09a bulletin revisits the sendmail/syslog vulnerabilities that were
reported earlier in CERT ADVISORY CA-95:13.  Since the release of
CA-95:13, updated patch information has been obtained from several
vendors. This updated information appears in Appendix A of this
bulletin (this was originally supplied by CERT).

The previous CIAC Bulletin G-09 referred to vulnerabilities with SMTP
"EXPN" and "VRFY" commands. The SMTP vulnerability is a result of a
vulnerability in syslog. The syslog(3) subroutine uses an internal
buffer for building messages that are sent to the syslogd(8)
daemon. The syslog subroutine does not check boundaries on data stored
in this buffer. It is possible to overflow the internal buffer and
rewrite the subroutine call stack. It is then possible to execute
arbitrary programs.

Most versions of sendmail prior to Version 8.6.10, including Sendmail
5.67+IDA-1.5 and most vendor versions, contain the syslog
vulnerability that could allow unauthorized root access. CIAC has
received information that the syslog vulnerability is being exploited
with a script that has been written to be used with sendmail.

Successful exploitation of this vulnerability allows an attacker to
execute arbitrary commands on the local system with super-user
("root") permissions and gain unrestricted access to system resources.


The first three recommendations are specific to sendmail and do not
address the problem with syslog. Most vendors are directing efforts to
patch syslog, thus fixing the core problem. CIAC recommends installing
vendor patches when available. If vendor patches are not available,
consider implementing the first three recommendations A, B, and C. The
best solution is dependent on your operating environment.

Note that sendmail workarounds do not resolve the syslog
vulnerability. Other programs and applications that call syslog are
still vulnerable. After vendor patches are installed, it is necessary
to rebuild executables that are statically linked.

A. Install Sendmail Version 8.7.3.  

Sendmail 8.7.3 does boundary checking for "EXPN" and "VRFY" commands.
Sendmail 8.7.3 is available via the Internet by anonymous FTP from: ( 

    MD5 (sendmail.8.7.3.tar.Z) = 3c3891c92500d12d60a61aaa1d01b533

B. Install "smap" and "smapd" programs 

The "smap" program provides a minimal SMTP implementation that accepts
mail messages from the network and stores them for later delivery.
The "smapd" program periodically runs "sendmail" on these stored
messages and thus sendmail is no longer reachable directly from the
network and its security vulnerabilities can no longer be exploited.

The "smap" and "smapd" programs are part of the Trusted Information
Systems (TIS) Firewall Toolkit available from TIS, Inc.  TIS Toolkit
is available on the Internet via anonymous FTP; you will need the
files: (

    MD5 (fwtk.tar.Z) = 5388b86a01300e7525d3cc1c36aab523

NOTE: Installation of "smap" and "smapd" is relatively simple, but 
it does represent a significant change in the way electronic mail 
will be handled at your site.  Careful consideration should 
be given to requirements and installation options, and entensive 
testing should be performed prior to site-wide deployment.

C. Disable the "EXPN" and "VRFY" commands 

Disabling the "EXPN" and "VRFY" commands in your current version of
the "sendmail" will prohibit an attacker from exploiting the

   1. Sendmail versions 8.6.x or 8.7.x:
   Sendmail Version 8 provides the "p" configuration file option 
   that allows you to configure the privacy and security features 
   of your "sendmail" process.  The format of the option is:


   where "what" is one of several keywords that enable the 
   various features.  By listing the "noexpn" and "novrfy" 
   keywords in this list, you can disable access to the "EXPN" and 
   "VRFY" commands.  After adding (or changing) this line in your 
   configuration file, you must kill and restart the "sendmail" 

   2. Sendmail versions other than 8.6.x or 8.7.x:
   Prior to Version 8, there is no way to disable these commands
   through the configuration file or the command line.  However, 
   the commands can be disabled by patching the "sendmail" binary
   as follows:

      A. Make a backup copy of the sendmail binary. Patching binary 
      files is not always successful and you will need to be able 
      to recover.

      # cp -p /usr/lib/sendmail /usr/lib/
      # chmod 700 /usr/lib/
      B. Use the "strings" command to find the addresses of the 
      "vrfy" and "expn" command name strings:

      # strings -o /usr/lib/sendmail | grep vrfy
       240248 novrfy
       240264 needvrfyhelo
       276648 vrfy
      # strings -o /usr/lib/sendmail | grep expn
       240256 noexpn
       240280 needexpnhelo
       276640 expn
       280328 expn

      NOTE: The output you see may be different: the important
      information to use are the numbers returned in front of the
      "expn" and "vrfy" strings.

      C. Use "adb" to write a null byte on each of these commands.  
      Note: Use the addresses output by your run of the "strings" 
      command, not the numbers from the example above. 

      # adb -w - /usr/lib/sendmail
       not core file = /usr/lib/sendmail
       a$d                     <-- converts to decimal addresses
       276648/w 0              <-- writes zero byte on "vrfy"
       0x438a8:        30322   =       0
       276640/w 0              <-- writes zero byte on first "expn"
       0x438a0:        25976   =       0
       280328/w 0              <-- writes zero byte on second "expn"
       0x44708:        25976   =       0
       ^D                      <-- CTRL-D exits adb

      D. Verify the strings were removed:

      # strings -o /usr/lib/sendmail | grep vrfy
       240248 novrfy
       240264 needvrfyhelo
      # strings -o /usr/lib/sendmail | grep expn
       240256 noexpn
       240280 needexpnhelo

      E. Kill and restart the "sendmail" daemon.  NOTE: Some mail 
      user agents (the programs that users use to read and send mail) 
      rely on the presence of the "VRFY" command which you just 
      disabled.  After performing the above steps, test all of the 
      mail programs in use at your site to insure that they still 
      operate correctly.

D. Install vendor patches

Install the appropriate "sendmail" and/or "syslog" patches from your
vendor. Some vendors currently have patches available while others
are in the process. Please check with your vendor and install patches
when they are available. 

Appendix A contains CIAC's update to the CERT(sm) Coordination
Center's CA-95:13.README which contains vendor information.


Appendix A is an update to CA-95:13.README that contains information
from vendors regarding syslog patches. The CERT README file can be
obtained from:

As of February 1, 1996, CIAC has additional information concerning
vendor patch status in CA-95:13.README. These changes are reflected in
the following vendor entries:

        Eric Allman
        Cray Research
        Hewlett-Packard Company       (updated 2/12/96)
        Silicon Graphics Inc.
        Sun Microsystems, Inc.

Revisions are identified by the revison bar "=" in column one.  
NOTE: CERT staff will be revising their README file to incorporate
these updates as well.


Below is information received from vendors concerning the
vulnerability described in this advisory. If you do not see your
vendor's name, please contact the vendor directly for information.

=CERT reported in CERT-95:13 that this problem is present in virtually
=all versions of the UNIX Operating System except the following:
=        Sony's NEWS-OS 6.X
=        SunOS 5.5 (Solaris 2.5)
=        Linux with libc version 4.7.2 released in May, 1995

In addition to vendor information, note that the freely available Linux with
libc version 4.7.2, released May 1995, is not vulnerable.

- ---------------------
Eric Allman

=Sendmail version 8.7.3 is not vulnerable.  
=This version is available by anonymous FTP from
=   MD5 (sendmail.8.7.3.tar.Z) = 3c3891c92500d12d60a61aaa1d01b533

- ---------------------
Berkeley Software Design, Inc.

Users of BSD/OS V2.0 and V2.0.1 by Berkeley Software Design, Inc. should
install patch U201-001 which works for both versions. The patch is available
to all BSDI customers in: 

    MD5 (U201-001) = 88b3fd8c83a5926589d7b87b55bc4e14

- ---------------------
Convex Computer Corporation

Vulnerable:  ConvexOS (all releases)
             SPPUX (all releases)

A patch is being developed to address this vulnerability in currently
supported releases as detailed below.  Contact the Convex Technical
Assistance Center 1-800-952-0379 to obtain information and patches.

There are no known automated attack programs in existence for Convex or
SPP architectures.  Development of such a program would require access
to such a machine, as well as detailed knowledge of the architecture. 
However, the only completely secure work-around at this time would be to
disable sendmail (known to have been successfully attacked on other
architectures), as well as other daemons which can potentially log
user-supplied strings.  Note that the user-supplied strings do not have
to actually be routed by syslogd in order for this vulnerability to
occur.  At this time we do not have a canonical list of affected
software; sendmail is the only known-vulnerable agent.

It should also be noted that Convex machines make use of a "SPU"
workstation (also referred to as a "test station") which controls the
machine; these workstations are vulnerable if sendmail is enabled on
those workstations and the SPU or test station is located on an
accessible network.  Convex recommends disabling sendmail on SPU and
test-station workstations until a patch can be obtained from Convex.

Currently supported OS releases as of Sep 1, 1995:

        ConvexOS 10.1, 10.2, 11.0, 11.1
        SPPUX    3.x

- ---------------------
Cray Research

Information about fixes for the syslog problem can be found in FN #2011,
dated October 10, 1995. Customers should receive this information from 
their Cray Research service representative.

For all source installations, your Cray Research service representative can
obtain the fix via the getfix tool.

Due to the number of executables which use this library routine, it is not
possible to provide getfix packages for all binary installations. UNICOS
binary update packages and include this mod.

                         Release Level            Fix Package
 Affected Product        Containing Fix           Availability
 ================        ==============           ===========
= UNICOS 8.0             UNICOS *         source only
= UNICOS 8.3             **                       source only
= UNICOS 9.0             UNICOS ***       source only
= *   Released for all platforms.
= **  No more updates planned.
= *** Released for X-MP, Y-MP, C-90 and T-90 platforms but has not yet
=     released for YMP-EL and J-90 platforms.

- --------------------- 
Data General Corporation

  The DG/UX operating system is NOT vulnerable to this problem.  This
  includes all currently supported release, DG/UX 5.4 Release 3.00, DG/UX 5.4
  Release 3.10, DG/UX Release 4.10 and all related Trusted DG/UX products.

- ---------------------
Digital Equipment Corporation

As a modification to information provided at the time the CA-95:13
advisory was distributed, Digital Equipment Corporation has provided
the following additional information. 

This information, and additional details, was originally published
in Digital advisory SSRT0359, dated 29.NOV.1995.

This information is available via normal support channels or by access of
Digital's AES (advanced electronic services).

Symptoms of this vulnerability have been verified on:

	 ULTRIX V4.3 (VAX)       DEC OSF/1 V2.0,(V2.0B,V2.1,V2.1B)
	 ULTRIX V4.3 (MIPS)      DEC OSF/1 V3.0
	 ULTRIX V4.3A (MIPS)     DEC OSF/1 V3.0B
	 ULTRIX V4.4  (VAX)      DEC OSF/1 V3.2
	 ULTRIX V4.4 (MIPS)      DEC OSF/1 V3.2B      
	 ULTRIX V4.5 (MIPS)      DEC OSF/1 V3.2C     
	 ULTRIX V4.5 (VAX)       

Digital Equipment Corporation strongly urges Customers to upgrade to a minimum
of ULTRIX V4.3 (VAX / MIPS)  or  DEC OSF/1 V3.2, then apply  the appropriate
solution kit identified below. 

Digital has corrected this potential vulnerability and provided kits containing
new binaries. The appropriate kit and images are identified as follows:

   ULTRIX                        DEC OSF/1
   ------                        ---------
   ECO ID                        ECO ID
   SSRT0359_ULT45                SSRT0359_OSF1032C

   Image_Names                   Image_Names        
   Within the tar file           Within the tar file
   -----------------             -----------------  
   4.3/MIPS/sendmail             3.0b/
   4.3/MIPS/syslog.o             3.0b/libc.a      
   4.3/VAX/sendmail              3.0/      
   4.3/VAX/syslog.o              3.0/libc.a       
   4.3A/MIPS/sendmail            3.2b/     
   4.3A/MIPS/syslog.o            3.2b/libc.a      
   4.4/MIPS/sendmail             3.2c/     
   4.4/MIPS/syslog.o             3.2c/libc.a      
   4.4/VAX/sendmail              3.2/libc.a       
   4.4/VAX/syslog.o              3.2/      
   4.5/MIPS/sendmail             2.0/libc.a       
   4.5/MIPS/syslog.o             2.0/      

Please note that ECO SSRT0359_ULT45 contains a version of sendmail that
supersedes all previous sendmail related ECO's. 

The above kits can be obtained through your normal Digital support channels.
They may also be obtained via the public link domain;

	 - Please refer to the applicable Cover Letter and Readme files
	   information prior to the installation of the remedial 
	   solutions on your system.

NOTE: For non-contract/non-warranty customers orders - there may be a nominal 
      charge for the kits, to cover the costs of media and handling.

As always, Digital urges you to periodically review your system management and 
security procedures. 

Digital will continue to review and enhance the security features of its
products and work with customers to maintain and improve the security and
integrity of their systems.

- ---------------------
Hewlett-Packard Company

=The following information about fixes for the syslog problem is
=contained in the HP Vendor Bulletin HPSBUX9602-029 released February
=7, 1996 and also in the CIAC Bulletin G-11 released February 12, 1996.
=   Determine which patch is appropriate for your hardware platform
=   and operating system:
=          PHCO_6595 (series 700/800, HP-UX 10.0 & 10.01), or
=          PHCO_6598 (series 800, HP-UX 9.0 & 9.04), or
=          PHCO_6597 (series 700, HP-UX 9.0[1357]), or
=          PHCO_6224 (series 300/400, HP-UX 9.0, 9.01, 9.03 & 9.1), or
=          PHCO_6162 (series 700, HP-UX 9.08 BLS), or
=          PHCO_6161 (series 700, HP-UX 9.09 BLS), or
=          PHCO_6160 (series 700, HP-UX 9.09+ BLS), or
=          PHCO_6157 (series 700, HP-UX 10.09 BLS CMW). 
=        To obtain a copy of the HP SupportLine email service user's 
=        guide, send the following in the TEXT PORTION OF THE MESSAGE to
= (no Subject is required):
=                      send guide
=        The users guide explains the process for downloading HP-UX 
=        patches via email and other services available.
=        World Wide Web service for downloading of patches 
=        is available via our URL: (

- --------------------
IBM Corporation

        Both fixes are now currently available. Please reference the
        following fixes:
        AIX 4.1 - IX53718
        AIX 3.2 - IX53358

- ---------------------
Open Software Foundation

OSF cannot reproduce the security hole in OSF/1. However we have reproduced
the problem with syslog(3).  We have a fix for the syslog(3) problem. Support
customers should contact OSF for the fix. The fix will be included in the
OSF/1 R1.3.2 update release. 

- ---------------------
Silicon Graphics Inc.

=SGI does have pending information and this information will be available via
=anonymous ftp (
=Following information was obtained from README.patch.825.
=For the IRIX operating system versions 5.2, 5.3, 6.0, 6.0.1, and 6.1 
=an inst-able patch has been generated and made available via anonymous 
=ftp and/or your service/support provider.  The patch is number 825
=and will install on IRIX 5.2, 5.3, 6.0 and 6.0.1 .   
=The SGI anonymous ftp site is (   Patch
=825 can be found in the following directories on the ftp server:
=        ~ftp/Security
=                or 
=        ~ftp/Patches/5.2
=        ~ftp/Patches/5.3
=        ~ftp/Patches/6.0
=        ~ftp/Patches/6.0.1
=                        ##### Checksums #### 
=        The actual patch will be a tar file containing the following files:
=        Filename:                 README.patch.825
=        Algorithm #1 (sum -r):    01444 57 README.patch.825
=        Algorithm #2 (sum):       12914 57 README.patch.825
=        MD5 checksum:             98C010655D46A61F77D791A279493BAC
=        Filename:                 patchSG0000825
=        Algorithm #1 (sum -r):    37486 2 patchSG0000825
=        Algorithm #2 (sum):       62783 2 patchSG0000825
=        MD5 checksum:             37D9840567CB48C58F43FA10A83E2CC0
=        Filename:                 patchSG0000825.eoe_man
=        Algorithm #1 (sum -r):    51345 75 patchSG0000825.eoe1_man
=        Algorithm #2 (sum):       13139 75 patchSG0000825.eoe1_man
=        MD5 checksum:             7CB2968AB462CF3C4BBC78002F005EEF
=        Filename:                 patchSG0000825.eoe1_sw
=        Algorithm #1 (sum -r):    21533 381 patchSG0000825.eoe1_sw
=        Algorithm #2 (sum):       18413 381 patchSG0000825.eoe1_sw
=        MD5 checksum:             1BE858D769A51AA5A4D0754F03CC3124
=        Filename:                 patchSG0000825.idb
=        Algorithm #1 (sum -r):    41651 4 patchSG0000825.idb
=        Algorithm #2 (sum):       10648 4 patchSG0000825.idb
=        MD5 checksum:             05B2D1CE3D9804F45CBDEFC27A53CAB5

- ---------------------
Solbourne (Grumman)

Solbourne 2.5 is not vulnerable.

- ---------------------
Sony Corporation

NEWS-OS 6.0.3 and 6.1 are not vulnerable.

- ---------------------
Sun Microsystems, Inc.

SunOS 5.5 is not vulnerable.

Sun Microsystems has made the following patches available to address this 

        PATCH #     VERSION                 RELEASED
        ---------   -----------             ------------
	100891-13 - SunOS 4.1.3             Oct 27, 1995
	101558-07 - SunOS 4.1.3_U1          Oct 27, 1995
=	102545-04 - SunOS 4.1.4             Nov 16, 1995

	102903-01 - Solaris 2.3             Nov, 2, 1995
=       101945-36 - Solaris 2.4             Jan 11, 1996   
	102905-01 - Solaris 2.4_x86         Nov, 2, 1995

Contact Sun for the details on obtaining these patches.


CIAC wishes to acknowledge and thank CERT Coordination Center, ASSIST,
IBM-ERS, and all the vendors for providing the information contained
in this bulletin. A special thanks goes to Mark Abene for initial 
notification to vendors of the sendmail EXPN and VRFY vulnerability.

CIAC, the Computer Incident Advisory Capability, is the computer
security incident response team for the U.S. Department of Energy
(DOE) and the National Institute of Health (NIH). CIAC is located at
the Lawrence Livermore National Laboratory in Livermore,
California. CIAC is also a founding member of FIRST, the Forum of
Incident Response and Security Teams, a global organization
established to foster cooperation and coordination among computer
security teams worldwide.

CIAC services are available to DOE, DOE contractors, and the NIH. CIAC can be 
contacted at:
    Voice:    +1 510-422-8193
    FAX:      +1 510-423-8002
    STU-III:  +1 510-423-2604

For emergencies and off-hour assistance, DOE, DOE contractor sites,
and the NIH may contact CIAC 24-hours a day. During off hours (5PM -
8AM PST), call the CIAC voice number 510-422-8193 and leave a message,
or call 800-759-7243 (800-SKY-PAGE) to send a Sky Page. CIAC has two
Sky Page PIN numbers, the primary PIN number, 8550070, is for the CIAC
duty person, and the secondary PIN number, 8550074 is for the CIAC
Project Leader.

Previous CIAC notices, anti-virus software, and other information are 
available from the CIAC Computer Security Archive. 

   World Wide Web:
   Anonymous FTP: (
   Modem access:        +1 (510) 423-4753 (14.4K baud)
                        +1 (510) 423-3331 (14.4K baud)

CIAC has several self-subscribing mailing lists for electronic publications:
1. CIAC-BULLETIN for Advisories, highest priority - time critical information 
   and Bulletins, important computer security information;
2. CIAC-NOTES for Notes, a collection of computer security articles;
3. SPI-ANNOUNCE for official news about Security Profile Inspector (SPI) 
   software updates, new features, distribution and availability;
4. SPI-NOTES, for discussion of problems and solutions regarding the use of 
   SPI products.

Our mailing lists are managed by a public domain software package called 
ListProcessor, which ignores E-mail header subject lines. To subscribe (add 
yourself) to one of our mailing lists, send the following request as the 
E-mail message body, substituting CIAC-BULLETIN, CIAC-NOTES, SPI-ANNOUNCE or 
SPI-NOTES for list-name and valid information for LastName FirstName and 
PhoneNumber when sending

E-mail to
        subscribe list-name LastName, FirstName PhoneNumber
  e.g., subscribe ciac-notes OHara, Scarlett W. 404-555-1212 x36

You will receive an acknowledgment containing address, initial PIN, and 
information on how to change either of them, cancel your subscription, or 
get help. 

PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing
communities receive CIAC bulletins.  If you are not part of these
communities, please contact your agency's response team to report
incidents. Your agency's team will coordinate with CIAC. The Forum of
Incident Response and Security Teams (FIRST) is a world-wide
organization. A list of FIRST member organizations and their
constituencies can be obtained by sending email to
with an empty subject line and a message body containing the line:
send first-contacts.

This document was prepared as an account of work sponsored by an agency of the
United States Government. Neither the United States Government nor the
University of California nor any of their employees, makes any warranty,
express or implied, or assumes any legal liability or responsibility for the
accuracy, completeness, or usefulness of any information, apparatus, product,
or process disclosed, or represents that its use would not infringe privately
owned rights. Reference herein to any specific commercial products, process,
or service by trade name, trademark, manufacturer, or otherwise, does not
necessarily constitute or imply its endorsement, recommendation or favoring by
the United States Government or the University of California. The views and
opinions of authors expressed herein do not necessarily state or reflect those
of the United States Government or the University of California, and shall not
be used for advertising or product endorsement purposes.

LAST 10 CIAC BULLETINS ISSUED (Previous bulletins available from CIAC)

(F-27)  Incorrect Permissions on /tmp
(F-28)  Vulnerability in SunOS 4.1.* Sendmail (-oR option)
(G-01)  Telnetd Vulnerability
(G-02)  SunOS 4.1.X Loadmodule Vulnerability
(G-03)  AOLGOLD Trojan Program
(G-04)  X Authentication Vulnerability
(G-05)  HP-UX FTP Vulnerability Bulletin
(G-06A) Win95 Vulnerabilities 
(G-07)  SGI Object Server Vulnerability 
(G-08)  splitvt(1) vulnerability 

RECENT CIAC NOTES ISSUED (Previous Notes available from CIAC)

Notes 07 - 3/29/95   A comprehensive review of SATAN

Notes 08 - 4/4/95    A Courtney update

Notes 09 - 4/24/95   More on the "Good Times" virus urban legend

Notes 10 - 6/16/95   PKZ300B Trojan, Logdaemon/FreeBSD, vulnerability
                     in S/Key, EBOLA Virus Hoax, and Caibua Virus

Notes 11 - 7/31/95   Virus Update, Hats Off to Administrators,
                     America On-Line Virus Scare, SPI 3.2.2 Released, 
                     The Die_Hard Virus

Notes 12 - 9/12/95   Securely configuring Public Telnet Services, X Windows, 
                     beta release of Merlin, Microsoft Word Macro Viruses,
                     Allegations of Inappropriate Data Collection in Win95

Version: 2.6.2


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