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samba-mirror/source4/scripting/bin/nsupdate-gss
Stefan Metzmacher ee30821eca CVE-2016-2125: s4:scripting: don't use GSS_C_DELEG_FLAG in nsupdate-gss
This is just an example script that's not directly used by samba,
but we should avoid sending delegated credentials to dns servers.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=12445

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Alexander Bokovoy <ab@samba.org>
Reviewed-by: Simo Sorce <idra@samba.org>
2016-12-20 07:51:14 +01:00

353 lines
8.3 KiB
Perl
Executable File

#!/usr/bin/perl -w
# update a win2000 DNS server using gss-tsig
# tridge@samba.org, October 2002
# jmruiz@animatika.net
# updated, 2004-Enero
# tridge@samba.org, September 2009
# added --verbose, --noverify, --ntype and --nameserver
# See draft-ietf-dnsext-gss-tsig-02, RFC2845 and RFC2930
use strict;
use lib "GSSAPI";
use Net::DNS;
use GSSAPI;
use Getopt::Long;
my $opt_wipe = 0;
my $opt_add = 0;
my $opt_noverify = 0;
my $opt_verbose = 0;
my $opt_help = 0;
my $opt_nameserver;
my $opt_realm;
my $opt_ntype = "A";
# main program
GetOptions (
'h|help|?' => \$opt_help,
'wipe' => \$opt_wipe,
'realm=s' => \$opt_realm,
'nameserver=s' => \$opt_nameserver,
'ntype=s' => \$opt_ntype,
'add' => \$opt_add,
'noverify' => \$opt_noverify,
'verbose' => \$opt_verbose
);
#########################################
# display help text
sub ShowHelp()
{
print "
nsupdate with gssapi
Copyright (C) tridge\@samba.org
Usage: nsupdate-gss [options] HOST DOMAIN TARGET TTL
Options:
--wipe wipe all records for this name
--add add to any existing records
--ntype=TYPE specify name type (default A)
--nameserver=server specify a specific nameserver
--noverify don't verify the MIC of the reply
--verbose show detailed steps
";
exit(0);
}
if ($opt_help) {
ShowHelp();
}
if ($#ARGV != 3) {
ShowHelp();
}
my $host = $ARGV[0];
my $domain = $ARGV[1];
my $target = $ARGV[2];
my $ttl = $ARGV[3];
my $alg = "gss.microsoft.com";
#######################################################################
# signing callback function for TSIG module
sub gss_sign($$)
{
my $key = shift;
my $data = shift;
my $sig;
$key->get_mic(0, $data, $sig);
return $sig;
}
#####################################################################
# write a string into a file
sub FileSave($$)
{
my($filename) = shift;
my($v) = shift;
local(*FILE);
open(FILE, ">$filename") || die "can't open $filename";
print FILE $v;
close(FILE);
}
#######################################################################
# verify a TSIG signature from a DNS server reply
#
sub sig_verify($$)
{
my $context = shift;
my $packet = shift;
my $tsig = ($packet->additional)[0];
$opt_verbose && print "calling sig_data\n";
my $sigdata = $tsig->sig_data($packet);
$opt_verbose && print "sig_data_done\n";
return $context->verify_mic($sigdata, $tsig->{"mac"}, 0);
}
#######################################################################
# find the nameserver for the domain
#
sub find_nameserver($)
{
my $server_name = shift;
return Net::DNS::Resolver->new(
nameservers => [$server_name],
recurse => 0,
debug => 0);
}
#######################################################################
# find a server name for a domain - currently uses the NS record
sub find_server_name($)
{
my $domain = shift;
my $res = Net::DNS::Resolver->new;
my $srv_query = $res->query("$domain.", "NS");
if (!defined($srv_query)) {
return undef;
}
my $server_name;
foreach my $rr (grep { $_->type eq 'NS' } $srv_query->answer) {
$server_name = $rr->nsdname;
}
return $server_name;
}
#######################################################################
#
#
sub negotiate_tkey($$$$)
{
my $nameserver = shift;
my $domain = shift;
my $server_name = shift;
my $key_name = shift;
my $status;
my $context = GSSAPI::Context->new;
my $name = GSSAPI::Name->new;
# use a principal name of dns/server@REALM
$opt_verbose &&
print "Using principal dns/" . $server_name . "@" . uc($opt_realm) . "\n";
$status = $name->import($name, "dns/" . $server_name . "@" . uc($opt_realm));
if (! $status) {
print "import name: $status\n";
return undef;
}
my $flags =
GSS_C_REPLAY_FLAG | GSS_C_MUTUAL_FLAG |
GSS_C_SEQUENCE_FLAG | GSS_C_CONF_FLAG |
GSS_C_INTEG_FLAG;
$status = GSSAPI::Cred::acquire_cred(undef, 120, undef, GSS_C_INITIATE,
my $cred, my $oidset, my $time);
if (! $status) {
print "acquire_cred: $status\n";
return undef;
}
$opt_verbose && print "creds acquired\n";
# call gss_init_sec_context()
$status = $context->init($cred, $name, undef, $flags,
0, undef, "", undef, my $tok,
undef, undef);
if (! $status) {
print "init_sec_context: $status\n";
return undef;
}
$opt_verbose && print "init done\n";
my $gss_query = Net::DNS::Packet->new("$key_name", "TKEY", "IN");
# note that Windows2000 uses a SPNEGO wrapping on GSSAPI data sent to the nameserver.
# I tested using the gen_negTokenTarg() call from Samba 3.0 and it does work, but
# for this utility it is better to use plain GSSAPI/krb5 data so as to reduce the
# dependence on external libraries. If we ever want to sign DNS packets using
# NTLMSSP instead of krb5 then the SPNEGO wrapper could be used
$opt_verbose && print "calling RR new\n";
$a = Net::DNS::RR->new(
Name => "$key_name",
Type => "TKEY",
TTL => 0,
Class => "ANY",
mode => 3,
algorithm => $alg,
inception => time,
expiration => time + 24*60*60,
key => $tok,
other_data => "",
);
$gss_query->push("answer", $a);
my $reply = $nameserver->send($gss_query);
if (!defined($reply) || $reply->header->{'rcode'} ne 'NOERROR') {
print "failed to send TKEY\n";
return undef;
}
my $key2 = ($reply->answer)[0]->{"key"};
# call gss_init_sec_context() again. Strictly speaking
# we should loop until this stops returning CONTINUE
# but I'm a lazy bastard
$status = $context->init($cred, $name, undef, $flags,
0, undef, $key2, undef, $tok,
undef, undef);
if (! $status) {
print "init_sec_context step 2: $status\n";
return undef;
}
if (!$opt_noverify) {
$opt_verbose && print "verifying\n";
# check the signature on the TKEY reply
my $rc = sig_verify($context, $reply);
if (! $rc) {
print "Failed to verify TKEY reply: $rc\n";
# return undef;
}
$opt_verbose && print "verifying done\n";
}
return $context;
}
#######################################################################
# MAIN
#######################################################################
if (!$opt_realm) {
$opt_realm = $domain;
}
# find the name of the DNS server
if (!$opt_nameserver) {
$opt_nameserver = find_server_name($domain);
if (!defined($opt_nameserver)) {
print "Failed to find a DNS server name for $domain\n";
exit 1;
}
}
$opt_verbose && print "Using DNS server name $opt_nameserver\n";
# connect to the nameserver
my $nameserver = find_nameserver($opt_nameserver);
if (!defined($nameserver) || $nameserver->{'errorstring'} ne 'NOERROR') {
print "Failed to connect to nameserver for domain $domain\n";
exit 1;
}
# use a long random key name
my $key_name = int(rand 10000000000000);
# negotiate a TKEY key
my $gss_context = negotiate_tkey($nameserver, $domain, $opt_nameserver, $key_name);
if (!defined($gss_context)) {
print "Failed to negotiate a TKEY\n";
exit 1;
}
$opt_verbose && print "Negotiated TKEY $key_name\n";
# construct a signed update
my $update = Net::DNS::Update->new($domain);
$update->push("pre", yxdomain("$domain"));
if (!$opt_add) {
$update->push("update", rr_del("$host.$domain. $opt_ntype"));
}
if (!$opt_wipe) {
$update->push("update", rr_add("$host.$domain. $ttl $opt_ntype $target"));
}
my $sig = Net::DNS::RR->new(
Name => $key_name,
Type => "TSIG",
TTL => 0,
Class => "ANY",
Algorithm => $alg,
Time_Signed => time,
Fudge => 36000,
Mac_Size => 0,
Mac => "",
Key => $gss_context,
Sign_Func => \&gss_sign,
Other_Len => 0,
Other_Data => "",
Error => 0,
mode => 3,
);
$update->push("additional", $sig);
# send the dynamic update
my $update_reply = $nameserver->send($update);
if (! defined($update_reply)) {
print "No reply to dynamic update\n";
exit 1;
}
# make sure it worked
my $result = $update_reply->header->{"rcode"};
($opt_verbose || $result ne 'NOERROR') && print "Update gave rcode $result\n";
if ($result ne 'NOERROR') {
exit 1;
}
exit 0;