SIP Attack Handling (Kamailio World 2021)

Kamailio World 2021
Fred Posner
@fredposner
SIP Attack Handling

SIP Attack Handling: Agenda
●
Introduction
●
Kamailio Modules
●
Kamailio Config
●
Other Handling
●
APIBAN

Who am I?
●
I’m Fred
●
Matrix:
@fred:matrix.lod.com
●
Twitter: @fredposner
●
VoIP Consultant
●
Based in Florida

What do you mean by SIP attack?
●
Unwanted SIP Traffic
●
Script Kiddie
●
Fuzzing
●
UDP/TCP/TLS
●
SQL Injection

Main Risks
●
Denial of Service
●
Fraud
●
Unauthorized Access
●
Compromised Data

Example
2021/08/28 12:23:37.123621 193.46.255.203:64932 ->
192.168.7.63:5060
INVITE sip:+421332304403@XXXX SIP/2.0
Via: SIP/2.0/UDP
193.46.255.203:64932;branch=z9hG4bK1444585349
Max-Forwards: 70
From: <sip:7000@XXXX>;tag=204899679
To: <sip:+421332304403@XXXX>
Call-ID: 1621039940-1946143325-953698149
CSeq: 1 INVITE
Contact: <sip:7000@193.46.255.203:64932>
Content-Type: application/sdp
Content-Length: 208
Allow: ACK, BYE, CANCEL, INFO, INVITE, MESSAGE, NOTIFY,
OPTIONS, PRACK, REFER, REGISTER, SUBSCRIBE, UPDATE,
PUBLISH
User-Agent: Linksys-SPA942
v=0
o=7000 16264 18299 IN IP4 192.168.1.83
s=call
c=IN IP4 192.168.1.83
t=0 0
m=audio 25282 RTP/AVP 0 101
a=rtpmap:0 pcmu/8000
a=rtpmap:8 pcma/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-11

Example
2021/08/28 12:32:18.516537 193.46.255.195:59160 ->
192.168.7.63:5060
INVITE sip:0046812400356@XXXX SIP/2.0
Via: SIP/2.0/UDP
193.46.255.195:59160;branch=z9hG4bK1663022028
Max-Forwards: 70
From: <sip:120@XXXX>;tag=2056781479
To: <sip:0046812400356@XXXX>
Call-ID: 1605879512-581542184-1615033911
CSeq: 1 INVITE
Contact: <sip:120@193.46.255.195:59160>
Content-Type: application/sdp
Content-Length: 207
Allow: ACK, BYE, CANCEL, INFO, INVITE, MESSAGE, NOTIFY,
OPTIONS, PRACK, REFER, REGISTER, SUBSCRIBE, UPDATE,
PUBLISH
User-Agent: Linksys-SPA942
v=0
o=120 16264 18299 IN IP4 192.168.1.83
s=call
c=IN IP4 192.168.1.83
t=0 0
m=audio 25282 RTP/AVP 0 101
a=rtpmap:0 pcmu/8000
a=rtpmap:8 pcma/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-11

Kamailio Modules: PIKE
●
Tracks number of SIP
messages per IP per
period of time.
●
Supports ipv4, ipv6
●
Easy to implement

loadmodule "pike.so"
...
modparam("pike",
"sampling_time_unit", 2)
modparam("pike",
"reqs_density_per_unit", 20)
modparam("pike",
"remove_latency", 4)
route {
if (!pike_check_req()) {
xlog("L_ALERT","ALERT:
pike block $rm from $fu
(IP:$si:$sp)n");
exit;
}

●
Pairs beautifully with
HTABLE/DMQ
●
Use ds lists, AUTH,
HTABLE, etc. to skip
nodes allowing high
traffic.

Kamailio Modules: SECFILTER
●
Lists for allow/block
by user-agent, ip,
country, domains,
users
●
SQL injection block

loadmodule "geoip2.so"
loadmodule "secfilter.so"
...
modparam("secfilter",
"db_url", DBURL)
modparam("secfilter",
"dst_exact_match", 0)
if (geoip2_match("$si", "src")) {
secf_check_country($gip2(src=>cc));
# return values ...
# 2 = allow list
# 1 = not found
# -1 = error
# -2 = block list
if ($? == -2) {
xalert("$rm from $si blocked because
Country '$gip2(src=>cc)' is in block list");
exit;
}
}

secf_check_from_hdr();
# return values ...
# 4 = name allowed
# 3 = domain allowed
# 2 = user allowed
# 1 = not found
# -1 = error
# -2 = user in block list
# -3 = domain in block list
# -4 = name in block list
switch ($?) {
case -2:
xalert("$rm to $si blocked because From user '$fU' is in block list");
exit;
case -3:
xalert("$rm to $si blocked because From domain '$fd' is in block list");
case -4:
xalert("$rm to $si blocked because From name '$fn' is in block list");
exit;
};
if (is_method("INVITE")) {
secf_check_dst($rU);
if ($? == -2) {
xalert("$rm from $si blocked
because destination $rU is in
block list");
exit;
}
}

Kamailio Modules: Other Modules
●
HTABLE
●
DMQ
●
PERMISSIONS
●
GEOIP/2
●
PHONENUM
●
PIPE/RATELIMIT

Kamailio Config
●
HTABLE is your best
friend
●
Temporarily block for
a period of time
●
Count occurrences

Temporarily Block
modparam("htable",
"htable",
"ipban=>size=8;autoexpire=3
00;dmqreplicate=1;")
●
5 min (300 s)
●
Replicate to all nodes
if($sht(ipban=>$si)!=$null) {
# ip is already blocked
xdbg("request from blocked IP - $rm from $fu (IP:$si:
$sp)n");
exit;
}
if(src_ip!=myself && !dmq_is_from_node() && !
ds_is_from_list()) {
xlog("L_INFO","[R-REQINT] pike blocking $rm from $fu (IP:
$si:$sp)n");
$sht(ipban=>$si) = 1;
exit;
}
}

Count Auth Attempts
...
modparam("htable", "htable", "a=>size=8;")
...
if(is_present_hf("Authorization"))
{
if($sht(a=>$au::auth_count)==3)
{
$var(exp) = $Ts - 900;
if($sht(a=>$au::last_auth) > $var(exp))
{
sl_send_reply("403", "Try later");
exit;
} else {
$sht(a=>$au::auth_count) = 0;
}
}
if(!www_authenticate("$td", "subscriber"))
{
switch ($retcode) {
case -1:
sl_send_reply("403", "Forbidden");
exit;
case -2:
if($sht(a=>$au::auth_count) == $null)
$sht(a=>$au::auth_count) = $sht(a=>$au::auth_count) + 1;
if($sht(a=>$au::auth_count) == 3)
xlog("auth failed 3rd time - src ip: $sin");
$sht(a=>$au::last_auth) = $Ts;
break;
}
www_challenge("$td"/*realm*/,"0"/*qop*/);
exit;
}
} else {
www_challenge("$td","0");
exit;
}

Count Anything
●
Failed REGISTERs
●
INVITEs
●
404s
●
Call Rate
●
International, etc.

Kamailio Config
●
XLOG
– Log when a block
happens
– Review logs
●
DIALOG
– Keep track of active
calls
– Works with DMQ

Kamailio Config
●
SANITY
if(!sanity_check("17895",
"7")) {
xlog("Malformed SIP
request from $si:$spn");
exit;
}
●
TOPOH/TOPOS
– Security by obscurity
●
Server Header / Agent
Header
– Version if you’re good
at updating

Other Handling
●
Update Kamailio
●
Update OS
●
Keep firewall, etc. up
to date

Fail2Ban
●
Blocking an IP
address in IP tables
performs better than
drop/exit/etc.
●
Bias:
I don’t like fail2ban
●
Bias:
I really don’t like
fail2ban

iptables-api
●
Simple API for adding &
removing ipaddresses
●
APIBANLOCAL chain
●
Open Source
●
https://github.com/
palner/iptables-api

iptables-api
loadmodule "http_client.so"
loadmodule "htable.so"
...
modparam("htable", "htable", "ipban=>size=8;autoexpire=60;")
...
xlog("L_ALERT","ALERT: pike blocking $rm from $fu (IP:$si:$sp)n");
$sht(ipban=>$si) = 1;
http_client_query("http://localhost:8082/addip/$si", "$var(apinfo)");
exit;
}
...
event_route[htable:expired:ipban] {
xlog("mytable record expired $shtrecord(key) => $shtrecord(value)n");
http_client_query("http://localhost:8082/removeip/$shtrecord(key)", "$var(apinfo)");
}

iptables-api
Aug 31 16:13:00 kamaPIlio
/usr/local/sbin/kamailio[5387]: WARNING: {1 1 ACK
11-520601@172.16.20.202} pike [pike_funcs.c:135]:
pike_check_ipaddr(): PIKE - BLOCKing ip
172.16.20.202, node=0x6594b390
/usr/local/sbin/kamailio[5387]: ALERT: {1 1 ACK 11-
520601@172.16.20.202} <script>: ALERT: pike
blocking ACK from sip:sipp@172.16.20.202:5060
(IP:172.16.20.202:5060)
/usr/local/sbin/kamailio[5397]: WARNING: pike
[pike_funcs.c:315]: refresh_node(): PIKE -
UNBLOCKing node 0x6594b390
/usr/local/sbin/kamailio[5397]: ERROR: <script>:
mytable record expired 172.16.20.202 => 1
2021/08/31 16:13:00 172.16.20.202
is a valid ip address
2021/08/31 16:13:00 IPTABLES
doesn't contain APIBANLOCAL.
Creating now...
2021/08/31 16:14:10 processing
removeIPAddress 172.16.20.202
2021/08/31 16:14:10
172.16.20.202 is a valid ip
address

APIBAN
●
Free (as in beer)
●
Community sharing of bad
actors via API
●
Honeypots
●
Client for IPTABLES or
example for Kamailio
●
https://apiban.org

Thank You for flying Kamailio
●
https://qxork.com
●
Fred Posner
●
@fredposner

SIP Attack Handling (Kamailio World 2021)

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