__________________________________________________________
The U.S. Department of Energy
Computer Incident Advisory Capability
___ __ __ _ ___
/ | /_\ /
\___ __|__ / \ \___
__________________________________________________________
INFORMATION BULLETIN
Unix sendmail vulnerability
January 31, 1996 15:00 GMT Number G-09
________________________________________________________________________________
PROBLEM: Sendmail (prior to Sendmail 8.6.10) contains a vulnerability
which allows local and remote users to execute privileged
commands
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: Upgrade to a latest version of Sendmail (current version is
8.7.3)
________________________________________________________________________________
VULNERABILITY This vulnerability is being actively exploited on the Internet
ASSESSMENT:
________________________________________________________________________________
The following information has been reprinted from the Automated
Systems Security Incident Support Team (ASSIST) 96-603 Bulletin.
[START ASSIST BULLETIN]
SUMMARY: All versions of "sendmail" prior to Version 8.6.10,
including Sendmail 5.67+IDA-1.5 and most vendor versions, contain
a vulnerability that could allow unauthorized root access. This
vulnerability is being actively exploited on the Internet.
BACKGROUND: The vulnerability is exploited through the use of the SMTP
"EXPN" and "VRFY" commands offered by all versions of "sendmail." A
buffer-overrun problem is present in the implementation of these
commands that allows the executable code of the "sendmail" process to
be overwritten. This executable code can do anything the author
wants, and is run with super-user permissions.
This vulnerability was fixed in Sendmail Version 8.6.10, which was
released on 21 February 1995. The current version of Sendmail is
8.7.3, which was released on 3 December 1995. The versions of
"sendmail" provided by most UNIX workstation vendors are based on
Versions 5.64, 5.65, or 5.67. Unless the vendor has taken
considerable care to secure their version of "sendmail" (most vendors
have not), these versions are vulnerable to this problem. The only
vendor version of "sendmail" that has been confirmed as not vulnerable
to this problem is the one shipped with Solaris 2.5 (but not earlier
versions of Solaris) from Sun Microsystems; this version is based on
"sendmail" 8.6.12. The "IDA" version of "sendmail," a popular public
domain version that offers enhanced mail delivery and user database
features, is based on Version 5.67, and is thus vulnerable to this
problem.
IMPACT: 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.
RECOMMENDED SOLUTIONS:
There are four possible solutions to this problem:
A. Install Sendmail Version 8.7.3. This version of "sendmail" is
under active development and offers major improvements, especially
in the area of security. Sendmail 8.7.3 is available via the
Internet by anonymous FTP from ftp.cs.berkeley.edu (128.32.35.31)
in /ucb/sendmail/sendmail.8.7.3.tar.Z. Other information
resources for sendmail are the "comp.mail.sendmail" USENET
newsgroup and the book "Sendmail," by Bryan Costales, Eric
Allman, and Neil Rickert, published by O'Reilly & Associates
(http://www.ora.com). Note: While compiling and installing a new
version of sendmail is not difficult, , modifying the
configuration file (the file that specifies how mail is to be
delivered) to work with the new version of the program is often
non-trivial. A complete rewrite of the existing configuration
file may be required, and this is a process that may require
several days at a minimum to complete. Option A is not
recommended unless you have extensive UNIX system administration
experience.
B. Install the "smap" and "smapd" programs on all UNIX systems
connected to the Internet. 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. The TIS is available on the Internet via anonymous FTP,
you will need the files:
/pub/firewalls/toolkit/fwtk.tar.Z and fwtk-doc-only.tar.Z
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 performed prior to site-wide deployment.
C. Disable the "EXPN" and "VRFY" commands in your current version
of the "sendmail" command. This will prohibit an attacker from
exploiting the vulnerability.
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:
Opwhat,what,what
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"
daemon.
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/sendmail.save
# chmod 700 /usr/lib/sendmail.save
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 note are the numbers 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 the appropriate "sendmail" patch from your vendor. At the
time this bulletin was issued, most major vendors were working this
matter. Some will ship fixes to customers, others will issue patches
that will be available for download. ASSIST will be sending out
updates to this bulletin as additional information becomes available.
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
ASSIST would like to thank the IBM-ERS for information contained in
this bulletin.
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
[END ASSIST BULLETIN]
________________________________________________________________________________
CIAC wishes to acknowledge ASSIST and IBM-ERS for providing the
information contained in this bulletin.
________________________________________________________________________________
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
E-mail: ciac@llnl.gov
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: http://ciac.llnl.gov/
Anonymous FTP: ciac.llnl.gov (128.115.19.53)
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 ciac-listproc@llnl.gov:
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 docserver@first.org
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-1) Telnetd Vulnerability
(G-2) SunOS 4.1.X Loadmodule Vulnerability
(G-3) AOLGOLD Trojan Program
(G-4) X Authentication Vulnerability
(G-5) 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
-----BEGIN PGP SIGNATURE-----
Version: 2.6.2
iQCVAwUBMQ/36LnzJzdsy3QZAQEJvQQAuytcMTTvjzaTpojcTaDFPGPz53mCFkwQ
i46mv5LZU32w8tED3+NNgn65fzG4VAvBXSLKC7thUzs/hnnn0RwSpmWOM6HKUwdw
LiDxNZftNBpMn3CldF4VjhwVOaVfHEwkIUWBDTwMKXDULTJS01UxXCBLRaUC3cPg
jgsSwjiRFow=
=rhvj
-----END PGP SIGNATURE-----
---
"Some call him the coolest cybernetic sidewalk surfer ever to hang-ten
on the shoulders of the Great Information Superhiway."
--- ifmail v.2.8.lwz
* Origin: Monolithic Diversified Enterprises (1:340/13@fidonet)
TUCoPS is optimized to look best in Firefox® on a widescreen monitor (1440x900 or better).
Site design & layout copyright © 1986-2024 AOH
