TUCoPS :: Unix :: General :: ciach007.txt

 __________________________________________________________
 The U.S. Department of Energy
 Computer Incident Advisory Capability
 ___ __ __ _ ___
 / | /_\ /
 \___ __|__ / \ \___
 __________________________________________________________
 INFORMATION BULLETIN
 Sendmail SIGHUP-smtpd Vulnerability
November 22, 1996 17:00 GMT Number H-07
______________________________________________________________________________
PROBLEM: Due to a coding error, a combination of user-level commands and
 use of the HUP signal, a user can force sendmail to execute an
 arbitary program with root privileges.
PLATFORM: Sendmail versions 8.7 through 8.8.2
DAMAGE: A user can obtain root privileges.
SOLUTION: Install the latest version of sendmail (8.8.3), or the patches
 from your vendor for your operating system (as listed below).
______________________________________________________________________________
VULNERABILITY Because of this vulnerability and several others in these and
ASSESSMENT: earlier versions of sendmail, it is highly recommended that you
 install the latest patches from your vendor or Sendmail version
 8.8.3 as soon as possible.
______________________________________________________________________________
[ Based on AUSCERT AA-96.10, CERT CA-96.24, and SGI#19961103-01-I ]
[ CIAC NOTE: Additional information on Silicon Graphics workstations precedes]
[ the original CERT Bulletin ]
[ Info from SGI Bulletin 19961103-01-I ]
| Silicon Graphics:
| ==============================
| Silicon Graphics has historically provided a version 8.6.x sendmail
| program. The most recent SGI sendmail patch (1502) provides a version
| 8.6.12 sendmail program also.
| 
| The versions of sendmail provided in the distributed Silicon Graphics IRIX
| operating system versions 5.2, 5.3, 6.0, 6.0.1, 6.1, 6.2 and 6.3 (and in
| SGI patch 1502, which is the latest released patch for sendmail) are not
| vulnerable to the exploitation as described in the CERT Advisory CA-96:24.
| 
| No further action is required.
[ End SGI Bulletin Excerpt 19961103-01-I ]
[ Begin CERT Advisory 96.24]
=============================================================================
CERT(sm) Advisory CA-96.24
Original issue date: November 21, 1996
Last revised: --
Topic: Sendmail Daemon Mode Vulnerability
- -----------------------------------------------------------------------------
The CERT Coordination Center has received reports of a serious security
problem in sendmail that affects versions 8.7 through 8.8.2. By exploiting
this vulnerability, any local user can gain root access. Exploitation details
involving this vulnerability have been widely distributed.
Independent of this new vulnerability, there are other security problems
with older sendmail versions. Even if you are not running a version between
8.7 and 8.8.2, we strongly encourage you to upgrade to the current version
of sendmail (8.8.3). See Section IV for details.
The CERT/CC team recommends installing vendor patches or upgrading to the
current version of sendmail (8.8.3). Until you can do so, we urge you to
apply the workaround provided in Section III.C. In all cases, be sure to
take the extra precautions listed in Section III.D.
We will update this advisory as we receive additional information. Please
check advisory files regularly for updates that relate to your site. In
addition, you can check ftp://info.cert.org/pub/latest_sw_versions/sendmail
to identify the most current version of sendmail.
- -----------------------------------------------------------------------------
I. Description
 Sendmail is often run in daemon mode so that it can "listen" for
 incoming mail connections on the standard SMTP networking port, usually
 port 25. The root user is the only user allowed to start sendmail this
 way, and sendmail contains code intended to enforce this restriction.
 Unfortunately, due to a coding error, sendmail can be invoked in daemon
 mode in a way that bypasses the built-in check. When the check is
 bypassed, any local user is able to start sendmail in daemon mode. In
 addition, as of version 8.7, sendmail will restart itself when it
 receives a SIGHUP signal. It does this restarting operation by
 re-executing itself using the exec(2) system call. Re-executing is done
 as the root user. By manipulating the sendmail environment, the user can
 then have sendmail execute an arbitrary program with root privileges.
II. Impact
 Local users can gain root privileges on the local machine.
III. Solution
 Install a patch from your vendor if one is available (Section A) or
 upgrade to the current version of sendmail (Section B). Until you can
 take one of those actions, we recommend applying the workaround described
 in Section C. In all cases, you should take the precautions described in
 Section D.
 A. Install a vendor patch.
 Below is a list of vendors who have provided information about
 sendmail. Details are in Appendix A of this advisory; we will update
 the appendix as we receive more information. If your vendor's name is
 not on this list, please contact the vendor directly.
 Berkeley Software Design, Inc. (BSDI)
 Data General Corporation
 Digital Equipment Corporation
 FreeBSD
 Hewlett-Packard Company
 IBM Corporation
 Linux
 NeXT Software, Inc.
 Open Software Foundation (OSF)
 The Santa Cruz Operation, Inc. (SCO)
 Sun Microsystems, Inc.
 B. Upgrade to the current version of sendmail.
 Install sendmail 8.8.3. This version is a "drop in" replacement for
 8.8.x. There is no patch for any version of sendmail before 8.8.0.
 If you are running such a version, strongly consider moving to
 version 8.8.3.
 Sendmail 8.8.3 is available from
 ftp://ftp.sendmail.org/ucb/src/sendmail/sendmail.8.8.3.tar.gz
 ftp://info.cert.org/pub/tools/sendmail/sendmail.8.8.3.tar.gz
 ftp://ftp.cert.dfn.de/pub/tools/net/sendmail/sendmail.8.8.3.tar.gz
 ftp://ftp.auscert.org.au/pub/mirrors/ftp.cs.berkeley.edu/ucb/sendmail/*
 MD5 (sendmail.8.8.3.tar.gz) = 0cb58caae93a19ac69ddd40660e01646
 Also in that directory are .Z and .sig files. The .Z file contains
 the same bits as the .gz file, but is compressed using UNIX compress
 instead of gzip. The .sig is Eric Allman's PGP signature for the
 uncompressed tar file. The key fingerprint is
 Type bits/keyID Date User ID
 pub 1024/BF7BA421 1995年02月23日 Eric P. Allman <eric@CS.Berkeley.EDU>
 Key fingerprint = C0 28 E6 7B 13 5B 29 02 6F 7E 43 3A 48 4F 45 29
 Eric P. Allman <eric@Reference.COM>
 Eric P. Allman <eric@Usenix.ORG>
 Eric P. Allman <eric@Sendmail.ORG>
 Eric P. Allman <eric@CS.Berkeley.EDU>
 When you change to a new version of sendmail, we strongly recommend
 also changing to the configuration files that are provided with that
 version. Significant work has been done to make this task easier.
 (In fact, it is highly likely that older configuration files will
 not work correctly with sendmail version 8.) It is now possible to
 build a sendmail configuration file (sendmail.cf) using the
 configuration files provided with the sendmail release. Consult the
 cf/README file for a more complete explanation. Creating your
 configuration files using this method makes it easier to incorporate
 future changes to sendmail into your configuration files.
 Sun sendmail users: A paper is available to help you convert your
 sendmail configuration files from the Sun version of sendmail to one
 that works with sendmail version 8.8.x. The paper is entitled
 "Converting Standard Sun Config Files to Sendmail Version 8" and was
 written by Rick McCarty of Texas Instruments Inc. It is included in
 the distribution and is located in contrib/converting.sun.configs.
 C. Apply a workaround.
 Eric Allman, the author of sendmail, has provided the following
 workaround.
 This vulnerability relies on a coding error that has existed in
 sendmail since November 1982, allowing non-root users to start up an
 SMTP daemon by invoking sendmail as smtpd. However, that error did
 not have the current negative implications until sendmail added the
 ability to re-execute when a SIGHUP signal was received; this was
 added in 8.7.
 The anti-smtpd program given in Appendix B refuses to permit sendmail
 to be invoked as smtpd by a non-root user. It should be installed
 setuid root in place of sendmail (e.g., as /usr/sbin/sendmail or
 /usr/lib/sendmail, depending on your system); the real sendmail
 should be moved to another place. That location should be set in the
 REAL_SENDMAIL definition, and it should not be accessible by ordinary
 users. This permits the anti-smtpd program to moderate access to
 sendmail.
 D. Take additional precautions
 Regardless of which solution you apply, you should take these extra
 precautions to protect your systems. These precautions do not address
 the vulnerabilities described herein, but are recommended as good
 practices to follow for the safer operation of sendmail.
 * Use the sendmail restricted shell program (smrsh)
 With *all* versions of sendmail, use the sendmail restricted shell
 program (smrsh). You should do this whether you use vendor-supplied
 sendmail or install sendmail yourself. Using smrsh gives you
 improved administrative control over the programs sendmail executes
 on behalf of users.
 A number of sites have reported some confusion about the need to
 continue using the sendmail restricted shell program (smrsh) when
 they install a vendor patch or upgrade to a new version of
 sendmail. You should always use the smrsh program.
 smrsh is included in the sendmail distribution in the subdirectory
 smrsh. See the RELEASE_NOTES file for a description of how to
 integrate smrsh into your sendmail configuration file.
 smrsh is also distributed with some operating systems.
 * Use mail.local
 If you run /bin/mail based on BSD 4.3 UNIX, replace /bin/mail with
 mail.local, which is included in the sendmail distribution. As of
 Solaris 2.5 and beyond, mail.local is included with the standard
 distribution. It is also included with some other operating systems
 distributions, such as FreeBSD.
 Although the current version of mail.local is not a perfect
 solution, it is important to use it because it addresses
 vulnerabilities that are being exploited. For more details, see
 CERT advisory CA-95:02.
 To use mail.local, replace all references to /bin/mail with
 /usr/lib/mail.local. If you are using the M4(1)-based configuration
 scheme provided with sendmail 8.X, add the following to your
 configuration file:
 define(`LOCAL_MAILER_PATH', /usr/lib/mail.local)
 * WARNING: Check for setuid executable copies of old versions of
 mail programs
 If you leave setuid executable copies of older versions of
 sendmail installed in /usr/lib (on some systems, it may be
 installed elsewhere), the vulnerabilities in those versions could
 be exploited if an intruder gains access to your system. This
 applies to sendmail.mx as well as other sendmail programs. Either
 delete these versions or change the protections on them to be
 non-executable.
 Similarly, if you replace /bin/mail with mail.local, remember to
 remove old copies of /bin/mail or make them non-executable.
IV. Additional Notes
 Two other sendmail vulnerabilities are described in CERT advisory
 CA-96.20; see that advisory for details.
 Since the release of CA-96.20, two additional sendmail vulnerabilities
 have been discovered and fixed. By upgrading to sendmail version 8.8.3,
 the two problems, noted below, are also fixed. Note that the wrapper
 described in Section III.C does not address these vulnerabilities. The
 best advice is to upgrade to sendmail version 8.8.3.
 A. A vulnerability in sendmail Versions 8.8.0 and 8.8.1 has been
 discovered that allows remote users to execute arbitrary commands
 with root privileges. This vulnerability exploits exploiting a
 problem related to a buffer overflow when converting between 7-bit
 and 8-bit MIME messages. Versions prior to Version 8.8.0 do not
 contain this vulnerability. Versions before 8.7.6 contain other
 unrelated vulnerabilities. This vulnerability is fixed in version
 8.8.2 and beyond. The Australian Emergency Response Team (AUSCERT)
 issued an advisory on this vulnerability, AA-96.06a, available from
 http://www.auscert.org.au/
 ftp://ftp.auscert.org.au/pub/
 B. A problem in sendmail has been reported that permits users on a
 system to redirect any email in the queue addressed to an unqualified
 domain name to a host of their choosing; that is, they can steal queued
 email. In some versions of the resolver, they may also be able to
 steal queued email addressed to fully qualified addresses. This bug
 is believed to exist in all versions of sendmail up to and including
 8.8.0. It is fixed in version 8.8.1 and beyond.
Appendix A - Vendor Information
Below is a list of the vendors who have provided information for this
advisory. We will update this appendix as we receive additional information.
If you do not see your vendor's name, please contact the vendor directly.
Berkeley Software Design, Inc. (BSDI)
====================================
BSD/OS is vulnerable to the sendmail daemon problem and we have issued an
official patch (U210-029) which may be obtained from our mail-back patches
server at patches@BSDI.COM or via anonymous ftp from:
 ftp://ftp.bsdi.com/bsdi/patches/patches-2.1/U210-029
Data General Corporation
========================
The sendmail included with Data General's DG/UX is not subject to this
vulnerability.
Digital Equipment Corporation
=============================
DIGITAL Engineering is aware of these reported problems and testing is
currently underway to determine the impact against all currently supported
releases of DIGITAL UNIX and ULTRIX. Patches will be developed (as
necessary) and made available via your normal DIGITAL Support
channel. Notice will be through normal AES services and DIGITAL'S Web site
 http://www.service.digital.com/html/whats-new.html
FreeBSD
=======
All currently shipping releases of FreeBSD are affected, including the just
released 2.1.6. An update for 2.1.6 will be available shortly. This problem
has been corrected in the -current sources. In the mean time, FreeBSD users
should follow the instructions in the CERT advisory. Sendmail will compile
and operate "out of the box" on FreeBSD systems.
Hewlett-Packard Company
=======================
Sendmail daemon problem:
 Not Vulnerable HP-UX 9.X, 10.00, 10.01, 10.10
 Vulnerable HP-UX 10.2 with PHNE_8702 Patches in process
IBM Corporation
===============
See the appropriate release below to determine your action.
 AIX 3.2
 -------
 No fix required. AIX 3.2 sendmail is not vulnerable.
 AIX 4.1
 -------
 No fix required. AIX 4.1 sendmail is not vulnerable.
 AIX 4.2
 -------
 AIX 4.2 sendmail is vulnerable.
 APAR IX63068 will be available shortly.
 To determine if you have this APAR on your system, run the following
 command:
 instfix -ik IX63068
 To Order
 --------
 APARs may be ordered using Electronic Fix Distribution (via FixDist)
 or from the IBM Support Center. For more information on FixDist,
 reference URL:
 http://service.software.ibm.com/aixsupport/
 or send e-mail to aixserv@austin.ibm.com with a subject of "FixDist".
 IBM and AIX are registered trademarks of International Business Machines
 Corporation.
Linux
=====
Linux has provided these URLs for S.u.S.E. Linux:
 ftp://ftp.suse.de/suse_update/S.u.S.E.-4.3/sendmail
 ftp://ftp.gwdg.de/pub/linux/suse/suse_update/S.u.S.E.-4.3/sendmail
Checksums for the files in these directories:
 6279df0597c972bff65623da5898d5dc sendmail.tgz
 0c0d20eecb1019ab4e629b103cac485c sendmail-8.8.3.dif
 0cb58caae93a19ac69ddd40660e01646 sendmail-8.8.3.tar.gz
- -----
Caldera OpenLinux has released a security advisory, available from
 http://www.caldera.com/tech-ref/cnd-1.0/security/SA-96.06.html
- -----
Red Hat has patched sendmail 8.7.6. The fixes are available from
Red Hat Linux/Intel:
 rpm -Uvh ftp://ftp.redhat.com/updates/4.0/i386/sendmail-8.7.6-5.i386.rpm
Red Hat Linux/Alpha:
 rpm -Uvh ftp://ftp.redhat.com/updates/4.0/axp/sendmail-8.7.6-5.axp.rpm
NeXT Software, Inc.
===================
NeXT is not vulnerable to the problem described in Section IV.A.
NeXT is vulnerable to the problem described in Section IV.B, and it
will be fixed in release 4.2 of OpenStep/Mach.
Open Software Foundation (OSF)
==============================
OSF/1 R1.3 is not vulnerable to this problem.
The Santa Cruz Operation, Inc. (SCO)
====================================
SCO is investigating the problem and will have more information in the
near future.
If we find that patches are needed, please check the following URLs
and this advisory appendix.
 ftp://ftp.sco.com/SLS/README
 ftp://ftp.sco.com/SSE/README
Sun Microsystems, Inc.
======================
No Sun versions of sendmail are affected by this vulnerability.
-----
Appendix B - anti-smtpd.c
Below is the code for the anti-smtpd.c sendmail wrapper. Here is an example
of how to compile and install this wrapper. You may have to change these
commands for your system. Further, you may have to change the code for
anti-smtpd.c to get it to compile on your system. Finally, you may also have
to turn off sendmail before running these commands and then turn sendmail back
on after running them. Run these commands as root.
 # mkdir /usr/hidden
 # chmod 700 /usr/hidden
 # mv /usr/lib/sendmail /usr/hidden/sendmail
 # cc anti-smtpd.c -o anti-smtpd
 # mv anti-smtpd /usr/lib/sendmail
 # chmod u+s /usr/lib/sendmail
Here is the code for anti-smtpd.c:
#include <stdio.h>
#include <string.h>
#include <syslog.h>
#include <sysexits.h>
static char *Version = "Version 1.0 November 21, 1996";
/*
** Sendmail wrapper for CA-96:24 HUP to smtpd problem
**
** This is trivial -- it just ensures that sendmail cannot be
** invoked as smtpd.
**
** To install this, move the real sendmail into /usr/hidden,
** which should be a mode 700 directory owned by root. Install
** this program setuid root in place of sendmail.
*/
#ifndef REAL_SENDMAIL
# define REAL_SENDMAIL "/usr/hidden/sendmail"
#endif
main(argc, argv)
 int argc;
 char **argv;
{
 char *p;
 extern int errno;
 if (argc < 1)
 {
 fprintf(stderr, "sendmail: need a program name\n");
 exit(EX_USAGE);
 }
 p = strrchr(argv[0], '/');
 if (p == NULL)
 p = argv[0];
 else
 p++;
 if (strcmp(p, "smtpd") == 0 && getuid() != 0)
 {
 fprintf(stderr, "sendmail: cannot be invoked as smtpd\n");
 syslog(LOG_ALERT, "sendmail: invoked as smtpd by %d", getuid());
 exit(EX_USAGE);
 }
 execv(REAL_SENDMAIL, argv);
 fprintf(stderr, "sendmail: cannot exec %s: errno = %d\n",
 REAL_SENDMAIL, errno);
 exit(EX_OSFILE);
}
- -----------------------------------------------------------------------------
The CERT Coordination Center thanks Eric Allman and AUSCERT for their
contributions to the development of this advisory.
- -----------------------------------------------------------------------------
- ---------------------------------------------------------------------------
Copyright 1996 Carnegie Mellon University
This material may be reproduced and distributed without permission provided
it is used for noncommercial purposes and the copyright statement is
included.
CERT is a service mark of Carnegie Mellon University.
- ---------------------------------------------------------------------------
This file:
 ftp://info.cert.org/pub/cert_advisories/CA-96.24.sendmail.daemon.mode
 http://www.cert.org
 click on "CERT Advisories"
[ END CERT Bulletin ]
_______________________________________________________________________________
CIAC wishes to acknowledge the contributions of AUSCERT, CERT, Silicon 
Graphics and Eric Allman for the information contained in this bulletin.
_______________________________________________________________________________
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LAST 10 CIAC BULLETINS ISSUED (Previous bulletins available from CIAC)
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G-46: Vulnerabilities in Transarc DCE and DFS
G-47: Unix FLEXlm Vulnerabilities
G-48: TCP SYN Flooding and IP Spoofing Attacks
H-01: Vulnerabilities in bash
H-02: SUN's TCP SYN Flooding Solutions
H-03: HP-UX_suid_Vulnerabilities
H-04: HP-UX Ping Vulnerability
H-05: Internet Hoaxes
H-06: Sun libc/libnsl Vulnerabilities (Sun Bulletin #00137)
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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
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Notes 11 - 7/31/95 Virus Update, Hats Off to Administrators,
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