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Security Bulletin 9713 DISA Defense Communications System

June 2, 1997 Published by: DISN Security Coordination Center

(SCC@NIC.MIL) 1-(800) 365-3642

DEFENSE INFORMATION SYSTEM NETWORK

SECURITY BULLETIN

The DISN SECURITY BULLETIN is distributed by the DISN SCC (Security Coordination Center) under DISA contract as a means of communicating information on network and host security exposures, fixes, and concerns to security and management personnel at DISN facilities. Back issues may be obtained via FTP (or Kermit) from NIC.MIL [207.132.116.5] using login="anonymous" and password="guest". The bulletin pathname is scc/sec-yynn.txt (where "yy" is the year the bulletin is issued and "nn" is a bulletin number, e.g. scc/sec-9615.txt). They are also available on our WWW site at http://nic.mil.

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+ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - +

! !

! The following important advisory was issued by the Computer !

! Emergency Response Team (CERT) and is being relayed unedited !

! via the Defense Information Systems Agency's Security !

! Coordination Center distribution system as a means of !

! providing DISN subscribers with useful security information. !

! !

+ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - +

Topic: Vulnerability in suidperl (sperl)

- -----------------------------------------------------------------------------

The CERT Coordination Center has received reports of a buffer overflow condition in suidperl built from Perl 4.n and Perl 5.n distributions on UNIX systems. By calling this program with appropriately crafted parameters, unauthorized local users can execute arbitrary commands as root. This vulnerability is being actively exploited.

The CERT/CC team recommends installing a vendor patch if one is available (see Section III.B). Until you can do so, we recommend disabling suidperl (Section III.A). Two other alternatives are to install suidperl or sperl from version 5.003 source code along with the patch provided in Appendix B of this advisory (see also Section III.C), or upgrade to Perl version 5.004 (Section III.D). Note that Perl4 is no longer supported.

We will update this advisory as we receive additional information.

Please check our advisory files regularly for updates that relate to your site.

- -----------------------------------------------------------------------------

I. Description

On some systems, setuid and setgid scripts (scripts written in the C shell, Bourne shell, or Perl, for example, with the set user or group ID permissions enabled) are insecure due to a race condition in the kernel. For those systems, Perl versions 4 and 5 attempt to work around this vulnerability with a special program named suidperl, also known as sperl. This program attempts to emulate the set-user-ID and set-group-ID features of the kernel.

There is a buffer overflow condition in suidperl built from Perl 4.n and Perl 5.n distributions earlier than version 5.004. If this program is called with appropriately crafted parameters, an attacker can execute arbitrary commands as root. This vulnerability is being actively exploited.

II. Impact

Users executing Perl scripts with the setuid bit set can execute arbitrary commands with the effective uid of the owner of the Perl script. Attackers can execute commands as root.

III. Solution

Use the command in Section A to help you determine if your system is vulnerable and, if it is, to (optionally) disable the suidperl and sperl programs (see Section A). If you find that your system is vulnerable, replace the suidperl and sperl programs with new versions.

Section B describes how to do that if your site uses versions of suidperl and sperl that are provided as part of a vendor-supplied distribution. Sites that installed suidperl and sperl programs themselves from the Perl source distribution should patch the distribution as described in Section C or upgrade to version 5.004 as described in Section D. Note that Perl4 is no longer supported.

A. Determine if your system is vulnerable and disable vulnerable programs

To determine if a system is vulnerable to this problem and to disable the programs that are believed to be vulnerable, use the following find command or a variant. Consult your local system documentation to determine how to tailor the find program on your system.

After you have run this command on all your systems, they will no longer be vulnerable. Note that after disabling the suidperl and sperl programs, they will no longer be able to emulate the set-user-ID and set-group-ID features of the kernel.

You will need to run the find command on each system you maintain because the command examines files on the local disk only. Substitute the names of your local file systems for FILE_SYSTEM_NAMES in the example. Example local file system names are /, /usr, and /var. You must do this as root.

Note that this is one long command, though we have separated it onto five lines using back-slashes.

find FILE_SYSTEM_NAMES -xdev -type f -user root \

\( -name 'sperl4.[0-9][0-9][0-9]' \

• o -name 'sperl5.00[0-3]' \
• o -name 'suidperl' \) \
• perm -04000 -print -ok chmod ug-s '{}' \;

This command will find all files on a system that are

• only in the file system you name (FILE_SYSTEM_NAMES -xdev)
• regular files (-type f)
• owned by root (-user root)
• named appropriately (-name 'sperl4.[0-9][0-9][0-9]'
  • o -name 'sperl5.00[0-3]'
  • o -name 'suidperl')
• setuid root (-perm -04000)

Once found, those files will

• have their names printed (-print)
• have their modes changed, but only if you type `y'

B. Obtain and install the appropriate patch from your vendor

If your vendor ships suidperl or sperl, you may be vulnerable and need a patch. Appendix A contains information provided by the following vendors. If your vendor is not on this list, please contact the vendor directly.

Until you can install a patch, we recommend disabling suidperl. The find command above will help you do that. If you need suidperl or sperl, see the alternatives in Sections C and D below.

C. Install suidperl or sperl from 5.003 source code and apply a patch.

Follow the instructions below, which were provided by Chip Salzenberg.

If you would like to keep using setuid Perl scripts, fix Perl yourself by following these steps:

1. Go to your Perl 5.003 source directory, or else obtain a fresh

Perl 5.003 distribution from

http://www.perl.com/CPAN/src/5.0/perl5.003.tar.gz

or another CPAN archive accessible to you.

This file is approximately 1.5 megabytes in size.

2. Using the "patch" program, apply the patch that is enclosed below in Appendix B.

3. Build and install the patched Perl 5.003. (If you have never built Perl before, be sure to read the "INSTALL" file first.)

Perl 5.003 binaries that have had this patch applied, and therefore are safe from all known attacks, can be identified by the output of the "perl -v" command: the "locally applied patches" list will include "SUIDBUF - Buffer overflow fixes for suidperl security".

D. Install suidperl or sperl from 5.004 source code (no patch needed).

If you would like to upgrade to Perl version 5.004, follow these steps:

1. Obtain a fresh Perl 5.004 distribution from

http://www.perl.com/CPAN/src/5.0/perl5.004.tar.gz

or another CPAN archive accessible to you.

This file is approximately 2.5 megabytes in size.

2. Build and install Perl 5.004 according to the instructions given in the "INSTALL" file. Do NOT apply the patch.

Perl 5.004 binaries, which are safe from all known attacks, can be identified by the output of the "perl -v" command: it should say "This is perl, version 5.004". (Unlike the 5.003 patch mentioned in Section C, the "locally applied patches" list will NOT include "SUIDBUF - Buffer overflow fixes for suidperl security". The fact that it is version 5.004 is sufficient in this case.)

...........................................................................

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, the CERT/CC did not hear from that vendor. Please contact the vendor directly.

Berkeley Software Design, Inc. (BSDI)

=====================================

BSD/OS is vulnerable to the suidperl (sperl) buffer overflow problem. We will be releasing a patch for BSDI 3.0 and perl 5.003 and are currently working on patches for BSD/OS 3.0 and Perl 4.036. We will also be developing patches for the perl versions shipped with BSD/OS 2.1.

Cray Research - A Silicon Graphics Company

Cray Research does not ship perl as part of either Unicos or Unicos/mk.

Data General Corporation

The only perl executables that are shipped with DG/UX are:

/bin/perl

and

/bin/perl5 /* in R420 */

These are not set uid programs.

Hewlett-Packard Company

HP does not ship this product.

IBM Corporation

AIX versions do not have Perl as part of the standard product. However, the SP2's PSSP software does contain suidperl, but the program is not installed with the setuid bit set.

IBM and AIX are registered trademarks of International Business Machines Corporation.

Linux

Red Hat 4.2 is not vulnerable

Red Hat 4.1/4.0 you can get the upgraded RPM from ftp.redhat.com

If you wish to check whether you have the fixed perl run perl -v and

check for

Locally applied patches:

SUIDBUF - Buffer overflow fixes for suidperl security

The Santa Cruz Operation, Inc. (SCO)

====================================

suidperl is not included in any SCO products.

SCO CMW+ and SCO OpenServer do not have kernel support for setuid scripts, but you may have installed suidperl in order to emulate that functionality - in that case you should replace your version of perl with version 5.004, or patch your source code as noted in this advisory.

SCO UnixWare does have safe kernel support for setuid scripts so that suidperl is not necessary. If you have installed a version of perl that includes suidperl, you should remove suidperl and install a version of perl built so as not to require it.

Silicon Graphics, Inc. (SGI)

=============================

At this time, Silicon Graphics does not have any public information for this suidperl/sperl issue. Silicon Graphics has communicated with CERT and other external security parties and is actively investigating this issue. When more Silicon Graphics information (including any possible patches) is available for release, that information will be released via the SGI security mailing list, wiretap.

For subscribing to the wiretap mailing list and other SGI security related information, please refer to the Silicon Graphics Security Headquarters website located at:

http://www.sgi.com/Support/Secur/security.html

...........................................................................

Appendix B - Source Code Patch Information

The following patch information has been supplied by Chip Salzenberg. If you built suidperl or sperl from 5.003 source code, we encouraged you to apply this patch (see the explanation in Section III.C above).

Patch follows.

- --------------------------------------------------------------------------

Index: patchlevel.h

***************

+ ,"SUIDBUF - Buffer overflow fixes for suidperl security"

,NULL

};

! fputs("\n\t+ suidperl security patch", stdout);

fputs("\n\nCopyright 1987-1996, Larry Wall\n",stdout);

! fputs("\n\t+ two suidperl security patches", stdout);

fputs("\n\nCopyright 1987-1996, Larry Wall\n",stdout);

#ifdef MSDOS

{

! char tmpbuf[1200];

GV *gv;

! sprintf(tmpbuf,"::_<%s", name);

gv = gv_fetchpv(tmpbuf, TRUE, SVt_PVGV);

sv_setpv(GvSV(gv), name);

if (*name == '/' && (instr(name,"/lib/") || instr(name,".pm")))

- --- 59,80 ----

char *name;

{

! char smallbuf[256];

! char *tmpbuf;

! STRLEN tmplen;

GV *gv;

! tmplen = strlen(name) + 4;

! if (tmplen < sizeof smallbuf)

! tmpbuf = smallbuf;

! else

! New(603, tmpbuf, tmplen + 1, char);

! tmpbuf[0] = ':';

! tmpbuf[1] = ':';

! tmpbuf[2] = '_';

! tmpbuf[3] = '<';

! strcpy(tmpbuf + 4, name);

gv = gv_fetchpv(tmpbuf, TRUE, SVt_PVGV);

• if (tmpbuf != smallbuf)
• Safefree(tmpbuf);

! static char *scan_ident _((char *s, char *send, char *dest, I32 ck_uni)); static char *scan_inputsymbol _((char *start)); static char *scan_pat _((char *start));

! static char *scan_ident _((char *s, char *send, char *dest, STRLEN destlen, ! I32 ck_uni)); static char *scan_inputsymbol _((char *start)); static char *scan_pat _((char *start));

*************** static char *scan_str _((char *start));

! static char *scan_word _((char *s, char *dest, int allow_package, STRLEN *slp)); static char *skipspace _((char *s)); static void checkcomma _((char *s, char *name, char *what));

! static char *scan_word _((char *s, char *dest, STRLEN destlen, ! int allow_package, STRLEN *slp)); static char *skipspace _((char *s)); static void checkcomma _((char *s, char *name, char *what));

• static char too_long[] = "Identifier too long";

+

/* The following are arranged oddly so that the guard on the switch statement

• can get by with a single comparison (if the compiler is smart enough).

(allow_tick && *s == '\'') )

{

! s = scan_word(s, tokenbuf, allow_pack, &len);

if (check_keyword && keyword(tokenbuf, len))

return start;

- --- 479,483 ----

(allow_tick && *s == '\'') )

{

! s = scan_word(s, tokenbuf, sizeof tokenbuf, allow_pack, &len);

if (check_keyword && keyword(tokenbuf, len))

return start;

! char tmpbuf[512];

if (!send) /* has to be an expression */

- --- 851,855 ----

unsigned char un_char = 0, last_un_char; char *send = strchr(s,']');

! char tmpbuf[sizeof tokenbuf * 4];

if (!send) /* has to be an expression */

! scan_ident(s,send,tmpbuf,FALSE);

if ((int)strlen(tmpbuf) > 1 && gv_fetchpv(tmpbuf,FALSE, SVt_PV))

weight -= 100;

- --- 876,880 ----

weight -= seen[un_char] * 10;

if (isALNUM(s[1])) {

! scan_ident(s, send, tmpbuf, sizeof tmpbuf, FALSE);

if ((int)strlen(tmpbuf) > 1 && gv_fetchpv(tmpbuf,FALSE, SVt_PV))

weight -= 100;

*************** GV *gv;

*** 942,946 ****

{

char *s = start + (*start == '$');

! char tmpbuf[1024];

STRLEN len;

GV* indirgv;

- --- 946,950 ----

{

char *s = start + (*start == '$');

! char tmpbuf[sizeof tokenbuf];

STRLEN len;

GV* indirgv;

*************** GV *gv;

*** 952,956 ****

gv = 0;

}

! s = scan_word(s, tmpbuf, TRUE, &len);

if (*start == '$') {

if (gv || last_lop_op == OP_PRINT || isUPPER(*tokenbuf))

- --- 956,960 ----

gv = 0;

}

! s = scan_word(s, tmpbuf, sizeof tmpbuf, TRUE, &len);

if (*start == '$') {

if (gv || last_lop_op == OP_PRINT || isUPPER(*tokenbuf))

*************** yylex()

*** 1629,1633 ****

case '*':

if (expect != XOPERATOR) {

! s = scan_ident(s, bufend, tokenbuf, TRUE);

expect = XOPERATOR;

force_ident(tokenbuf, '*');

- --- 1633,1637 ----

case '*':

if (expect != XOPERATOR) {

! s = scan_ident(s, bufend, tokenbuf, sizeof tokenbuf, TRUE);

expect = XOPERATOR;

force_ident(tokenbuf, '*');

case '%':

if (expect != XOPERATOR) {

! s = scan_ident(s, bufend, tokenbuf + 1, TRUE);

if (tokenbuf[1]) {

expect = XOPERATOR;

- --- 1649,1653 ----

case '%':

if (expect != XOPERATOR) {

! s = scan_ident(s, bufend, tokenbuf + 1, sizeof tokenbuf - 1, TRUE);

if (tokenbuf[1]) {

expect = XOPERATOR;

*************** yylex()

*** 1748,1752 ****

s++;

if (s < bufend && isALPHA(*s)) {

! d = scan_word(s, tokenbuf, FALSE, &len);

while (d < bufend && (*d == ' ' || *d == '\t'))

d++;

- --- 1752,1756 ----

s++;

if (s < bufend && isALPHA(*s)) {

! d = scan_word(s, tokenbuf, sizeof tokenbuf, FALSE, &len);

while (d < bufend && (*d == ' ' || *d == '\t'))

d++;

}

! s = scan_ident(s-1, bufend, tokenbuf, TRUE);

if (*tokenbuf) {

expect = XOPERATOR;

- --- 1851,1855 ----

}

! s = scan_ident(s - 1, bufend, tokenbuf, sizeof tokenbuf, TRUE);

if (*tokenbuf) {

expect = XOPERATOR;

case '$':

if (s[1] == '#' && (isALPHA(s[2]) || strchr("_{$:", s[2]))) {

! s = scan_ident(s+1, bufend, tokenbuf+1, FALSE);

if (expect == XOPERATOR) {

if (lex_formbrack && lex_brackets == lex_formbrack) {

- --- 1960,1965 ----

case '$':

if (s[1] == '#' && (isALPHA(s[2]) || strchr("_{$:", s[2]))) {

! s = scan_ident(s + 1, bufend, tokenbuf + 1, sizeof tokenbuf - 1,

! FALSE);

if (expect == XOPERATOR) {

if (lex_formbrack && lex_brackets == lex_formbrack) { *************** yylex()

*** 1982,1986 ****

TOKEN(DOLSHARP);

}

! s = scan_ident(s, bufend, tokenbuf+1, FALSE);

if (expect == XOPERATOR) {

if (lex_formbrack && lex_brackets == lex_formbrack) {

- --- 1987,1991 ----

TOKEN(DOLSHARP);

}

! s = scan_ident(s, bufend, tokenbuf + 1, sizeof tokenbuf - 1, FALSE);

if (expect == XOPERATOR) {

if (lex_formbrack && lex_brackets == lex_formbrack) {

if (*s == '{' && strEQ(tokenbuf, "$SIG") &&

(t = strchr(s,'}')) && (t = strchr(t,'='))) {

! char tmpbuf[1024];

STRLEN len;

for (t++; isSPACE(*t); t++) ;

if (isIDFIRST(*t)) {

! t = scan_word(t, tmpbuf, TRUE, &len);

if (*t != '(' && perl_get_cv(tmpbuf, FALSE))

warn("You need to quote \"%s\"", tmpbuf);

- --- 2021,2029 ----

if (*s == '{' && strEQ(tokenbuf, "$SIG") &&

(t = strchr(s,'}')) && (t = strchr(t,'='))) {

! char tmpbuf[sizeof tokenbuf];

STRLEN len;

for (t++; isSPACE(*t); t++) ;

if (isIDFIRST(*t)) {

! t = scan_word(t, tmpbuf, sizeof tmpbuf, TRUE, &len);

if (*t != '(' && perl_get_cv(tmpbuf, FALSE))

warn("You need to quote \"%s\"", tmpbuf);

case '@':

! s = scan_ident(s, bufend, tokenbuf+1, FALSE);

if (expect == XOPERATOR)

no_op("Array",s);

- --- 2098,2102 ----

case '@':

! s = scan_ident(s, bufend, tokenbuf + 1, sizeof tokenbuf - 1, FALSE);

if (expect == XOPERATOR)

no_op("Array",s);

: !GvHV(gv) )))

{

! char tmpbuf[1024];

sprintf(tmpbuf, "Literal @%s now requires backslash",tokenbuf+1);

yyerror(tmpbuf);

- --- 2134,2138 ----

: !GvHV(gv) )))

{

! char tmpbuf[sizeof tokenbuf + 40];

sprintf(tmpbuf, "Literal @%s now requires backslash",tokenbuf+1);

yyerror(tmpbuf);

keylookup:

bufptr = s;

! s = scan_word(s, tokenbuf, FALSE, &len);

if (*s == ':' && s[1] == ':' && strNE(tokenbuf, "CORE"))

- --- 2298,2302 ----

keylookup:

bufptr = s;

! s = scan_word(s, tokenbuf, sizeof tokenbuf, FALSE, &len);

if (*s == ':' && s[1] == ':' && strNE(tokenbuf, "CORE"))

if (*s == '\'' || *s == ':' && s[1] == ':') {

! s = scan_word(s, tokenbuf + len, TRUE, &len);

if (!len)

croak("Bad name after %s::", tokenbuf);

- --- 2343,2348 ----

if (*s == '\'' || *s == ':' && s[1] == ':') {

! s = scan_word(s, tokenbuf + len, sizeof tokenbuf - len,

! TRUE, &len);

if (!len)

croak("Bad name after %s::", tokenbuf);

*************** yylex()

*** 2557,2561 ****

s += 2; d = s;

! s = scan_word(s, tokenbuf, FALSE, &len);

tmp = keyword(tokenbuf, len);

if (tmp < 0)

- --- 2563,2567 ----

s += 2; d = s;

! s = scan_word(s, tokenbuf, sizeof tokenbuf, FALSE, &len);

tmp = keyword(tokenbuf, len);

if (tmp < 0)

if (isIDFIRST(*s) || *s == '\'' || *s == ':') {

! char tmpbuf[128];

expect = XBLOCK;

! d = scan_word(s, tmpbuf, TRUE, &len);

if (strchr(tmpbuf, ':'))

sv_setpv(subname, tmpbuf);

- --- 3250,3256 ----

if (isIDFIRST(*s) || *s == '\'' || *s == ':') {

! char tmpbuf[sizeof tokenbuf];

expect = XBLOCK;

! d = scan_word(s, tmpbuf, sizeof tmpbuf, TRUE, &len);

if (strchr(tmpbuf, ':'))

sv_setpv(subname, tmpbuf);

{

if (isALNUM(*s))

*d++ = *s++;

- --- 4097,4112 ----

{

register char *d = dest;

• register char *e = d + destlen - 3; /* two-character token, ending NUL */ for (;;) {
• if (d >= e)
• croak(too_long);

*d++ = *s++;

*************** STRLEN *slp;

*** 4119,4129 ****

{

- --- 4129,4141 ----

I32 ck_uni;

{

register char *d;

• register char *e;
  char *bracket = 0;
  char funny = *s++;

s = skipspace(s);

d = dest;

if (isDIGIT(*s)) {

! while (isDIGIT(*s))

*d++ = *s++;

}

else {

for (;;) {

if (isALNUM(*s))

*d++ = *s++;

- --- 4146,4161 ----

s = skipspace(s); d = dest;

• e = d + destlen - 3; /* two-character token, ending NUL */ if (isDIGIT(*s)) {

! while (isDIGIT(*s)) {

! if (d >= e)

! croak(too_long);

*d++ = *s++;

+ }

}

else {

for (;;) {

• if (d >= e)
• croak(too_long);

*d++ = *s++;

- --------------------------------------------------------------------------

End of patch.

- -----------------------------------------------------------------------------

The CERT Coordination Center staff thanks Chip Salzenberg for supplying a fix, Larry Wall for tweaking the fix, and Warner Losh for his work on patches.

- -----------------------------------------------------------------------------

If you believe that your system has been compromised, contact the CERT Coordination Center or your representative in the Forum of Incident Response and Security Teams (see http://www.first.org/team-info/)

CERT/CC Contact Information

- ----------------------------

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

Using encryption

We strongly urge you to encrypt sensitive information sent by email. We can support a shared DES key or PGP. Contact the CERT/CC for more information.

Location of CERT PGP key

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

Getting security information

CERT publications and other security information are available from

CERT advisories and bulletins are also posted on the USENET newsgroup

comp.security.announce

To be added to our mailing list for advisories and bulletins, send

email to

cert-advisory-request@cert.org

In the subject line, type

SUBSCRIBE your-email-address

- ---------------------------------------------------------------------------

• Registered U.S. Patent and Trademark Office.

Copyright 1997 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.

The CERT Coordination Center is part of the Software Engineering Institute (SEI). The SEI is sponsored by the U.S. Department of Defense.

- ---------------------------------------------------------------------------

This file: ftp://info.cert.org/pub/cert_advisories/CA-97.17.sperl

http://www.cert.org

click on "CERT Advisories"

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

****************************************************************************

* *

• The point of contact for NIPRNET security-related incidents is the *
• ASSIST: *

* *

• E-mail address: ASSIST@ASSIST.MIL *

* *

• Telephone: 1-(800)-357-4231 (24 hours/day) *

* *

• You may also contact the Security Coordination Center (SCC) at the *
• NIC: *

* *

• E-mail address: SCC@NIC.MIL *

* *

• Telephone: 1-(800)-365-3642 *

* *

• NIC Help Desk personnel are available from 7:00 a.m.-7:00 p.m. EST, *
• Monday through Friday except on federal holidays. *

* *

****************************************************************************

PLEASE NOTE: Some users outside of the DOD computing communities may receive DISN Security Bulletins. If you are not part of the DOD community, please contact your agency's incident response team to report incidents. Your agency's team will coordinate with DOD. 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 service to the DOD community. Neither the United States Government nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, 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. The opinions of the authors expressed herein do not necessarily state or reflect those of the United States Government, and shall not be used for advertising or product endorsement purposes.