Download Verizon-DDOS - Columbia University

Columbia Verizon Research
Security:
VoIP Denial-of-Service (DoS)
Eilon Yardeni
Columbia University
Gaston Ormazabal
Verizon Labs
May 23, 2006
Agenda
 Project Overview
– Background
– What is the problem?
– Goals
 The SIP Threat Model
 DoS attack taxonomy
 Mitigation strategy
 Testbed and Validation strategy
 Demo
 Discussion
May 23, 2006
2
Background
 Previous project results
– Successfully implemented a large scale SIP-aware
dynamic pinhole filter (firewall)
– The filter is used as a first-line of defense against DoS
attacks at the network perimeter
 Only signaled media channels can traverse the perimeter
 End systems are protected against flooding of random RTP
or other packets
 But…attacks can still traverse the perimeter
through the signaling port and media ports
– Pinholes cannot distinguish legitimate from illegitimate
traffic
May 23, 2006
3
The Problem
 Attack traffic that traverses the perimeter
could target the availability of the signaling
VoIP services
 Telephony services migrating to IP become
an attractive DoS attack target
 Attack targets could be supporting services
(e.g. DNS), SIP infrastructure elements
(proxy, softswitch, SBC) and end-points (SIP
phones)
May 23, 2006
4
Goals
 Study VoIP DoS
–
–
–
–
Definition – define VoIP specific threats
Detection – how do we detect an attack?
Mitigation – defense strategy and implementation
Validation – validate our defense strategy
 Generate requirements for future security
network elements and test tools for their
validation
May 23, 2006
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The SIP Threat Model (1)
 Eavesdropping
 Impersonation of a SIP entity
 Interception and Modification of SIP
messages
 Service Abuse
 Denial of Service
• VoIP Security and Privacy Threat Taxonomy, VoIPSA October 2005
• RFC 3261, SIP: Session Initiation Protocol, June 2002
May 23, 2006
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The SIP Threat Model (2)
 Eavesdropping
– Attacker can monitor signaling/media streams, but
cannot or does not alter the data itself
– Signaling channel is not confidential
– Call Pattern Tracking
 Discovery of identity, affiliation, presence
– Traffic Capture
 Packet recording
– Number harvesting
 Unauthorized collection of numbers, emails, SIP URIs
May 23, 2006
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The SIP Threat Model (3)
 Impersonation of a SIP entity
– Impersonate a UA
 Absence of assurance of a request’s originator
 Registration Hijacking - attacker deregisters a legitimate
contact and registers its own device for that contact
– Impersonate a Server
 UAs should authenticate the server to whom they send
requests
 Attacker impersonates a remote server and intercepts
UA’s requests
May 23, 2006
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The SIP Threat Model (4)
 Interception and Modification of SIP
messages
– Man-in-the-middle attack
 UA is using SIP to communicate media session keys
– Call Rerouting
 Attacker might modify the SDP in order to route media
streams to a wiretapping device
– Conversation Degradation
 Attacker might cause intentional reduction in QoS
– False Call Identification
 Change “Subject” so message considered Spam
May 23, 2006
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The SIP Threat Model (5)
 Service Abuse
– Call Conference Abuse
 Hide identity for the purpose of committing fraud
– Premium Rate Service Fraud
 Artificially increase traffic in order to maximize billing
– Improper Bypass or Adjustment to Billing
 Avoid authorized service charge by altering billing
records
May 23, 2006
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Denial of Service (1)
 Denial-of-Service – preventing users from effectively
using the targeted services
– Complete loss of service
– Service degradation to a “not usable” point
 Distributed denial-of-service attacks continue to be
the main threat facing network operators*
 Most attacks involve compromised hosts (bots), with
botnets sized from a few thousands to over 100,000*
* - Worldwide ISP Security Report, September 2005, Arbor Networks
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Denial of Service (2)
* - Worldwide ISP Security Report, September 2005, Arbor Networks
May 23, 2006
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DoS Attack Taxonomy (1)
 Implementation flaws
 Application level
 Flooding
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DoS Attack Taxonomy (2)
 Implementation flaws
– Attacker sends carefully crafted packet(s) that
exploits a specific implementation flaw
– Might cause excessive memory/disk/CPU
consumption and/or system reboot or crash
– Target vulnerability could originate in different
levels of the network protocol stack or in the
underlying OS/firmware
May 23, 2006
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DoS Attack Taxonomy (3)
 Application level - a feature of SIP is
manipulated to cause a DoS attack
– Registration Hijacking
 Attacker registers his device with other user’s URI
– Call Hijacking
 Attacker can inject a “301 Moved Permanently” message
to an active session
– Modification of media sessions
 Attacker can spoof re-INVITE messages thereby
reducing QoS, redirecting media, modifying security
attributes
May 23, 2006
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DoS Attack Taxonomy (4)
 Application level (Cont.)
– Session teardown
 Attacker can spoof a BYE message and inject it to an
active session thereby tearing down the session
– Amplification attacks
 Attacker can create bogus requests with falsified Via
header field that identifies a target host
 UAs/proxies generates a DDoS against that target
– Media streams attack
 Attacker can inject spoofed RTP packets with high seq
numbers into a media stream thereby modifying playout
sequence
May 23, 2006
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DoS Attack Taxonomy (5)
 Flooding
– Attacker can flood the network link or overwhelm
the target host
– Usually requires more resources from the attacker
– Harder to defend against – even the best
maintained systems can become congested
– Variants could be: UDP floods, ICPM echo
attacks, SYN floods etc,.
– Floods of INVITE or REGISTER messages could
cause excessive processing at a SIP proxy
May 23, 2006
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Mitigation strategy (1)
 Implementation flaws are easier to deal with
– Systems can be tested before used in production
– Systems can be patched when a new flaw is discovered
– Attack signatures could be integrated with a firewall
 Application level and flooding attacks are harder to
defend against
 SIP end-points are “dumb” – try to defend SIP
infrastructure elements
 There are commercially available solutions for
general UDP/SYN flooding (Arbor Networks,
Cisco/Riverhead) but none for SIP
May 23, 2006
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Mitigation strategy (2)
 A common vulnerability to SIP over UDP attacks is
the ability to spoof SIP requests
–
–
–
–
Registration/Call Hijacking
Modification of media sessions
Session teardown
Requests flooding
 Perform return routability check
– For UDP use SIP’s built-in digest authentication mechanism
 Use null-authentication when no shared secret is established
 Rate-limit spoofed sources
– For TCP perform SYN relay
May 23, 2006
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SIP Digest Authentication (1)
User Agent
Client (UAC)
Proxy
Server
INVITE
Generate the
nonce value
407 Proxy Authentication
Required (nonce, realm..)
ACK
nonce – a uniquely generated
string used for one challenge only
and has a life time of X seconds
Compute response =
F(nonce, username, password, realm)
INVITE
(nonce, response…)
Authentication: compute
F(nonce, username, password, realm)
and compare with response
May 23, 2006
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SIP Digest Authentication (2)
 The introduction of digest
authentication accounts for
nearly 80% of processing cost
of a stateless server and 45%
of a call stateful server
 70% of additional cost is for
message processing and 30%
for authentication computation
(hashing)
SIP Security Issues: The SIP Authentication Procedure and its Processing Load,
May 23, 2006
Salsano et al., IEEE Network, November 2002
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Mitigation Solution
Overview
Untrusted
Trusted
Filter I
DPPM
SIP
Filter II
sipd
SIP
SIP
VoIP Traffic
RTP
RTP
Attack Traffic
May 23, 2006
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Mitigation Implementation (1)
 Use the CloudShield to rate-limit SIP authentication
attempts to the proxy
 Use the firewall controlling proxy model
 Columbia’s SIP Proxy sipd controls the CloudShield
2000 Deep Packet Inspection Server
– Utilize wire-speed deep packet inspection
– State is only kept at the CloudShield
– Utilize the Firewall Control Protocol to establish filters in real
time
– Insert filters for SIP UAs that are been challenged
May 23, 2006
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INVITE sip:[email protected] SIP/2.0
Via: SIP/2.0/UDP 128.59.21.70:5060
Max-Forwards: 70
From: sip:[email protected]
To: sip:[email protected]
Contact: sip:[email protected]:5060
Subject: sipstone invite test
CSeq: 1 INVITE
Call-ID: [email protected]
Content-Type: application/sdp
Content-Length: 211
INVITE sip:[email protected] SIP/2.0
Via: SIP/2.0/UDP 128.59.21.70:5060
SIP/2.0 407 Proxy Authentication Required
Max-Forwards: 70
Via: SIP/2.0/UDP 127.0.0.1:7898
From: sip:[email protected]
From: sip:[email protected]
To: sip:[email protected]
To: sip:[email protected];
Contact: sip:[email protected]:5060
tag=2cg7XX0dZQvUIlbUkFYWGA
Subject: sipstone invite test
Call-ID: [email protected]
CSeq: 3 INVITE
CSeq: 1 INVITE
Call-ID: [email protected]
Date: Fri, 14 Apr 2006 22:51:33 GMT
Content-Type: application/sdp
Server: Columbia-SIP-Server/1.24
Content-Length: 211
Content-Length: 0
Proxy-Authorization: Digest username="anonymous",
Proxy-Authenticate:
Digest realm="cs.columbia.edu",
Trusted
realm="cs.columbia.edu",
nonce="6ydARDP51P8Ef9H4iiHmUc7iFDE=",
nonce="6ydARDP51P8Ef9H4iiHmUc7iFDE=",
stale=FALSE,
uri="sip:[email protected]",
algorithm=MD5,
response="0480240000edd6c0b64befc19479924c",
qop="auth,auth-int"
opaque="", algorithm="MD5"
Mitigation Implementation (2)
Return-Routability Succeeds
SIP UA
v=0
o=user1 53655765 23587637 IN IP4 128.59.21.70
s=Mbone Audio
t=3149328700 0
i=Discussion of Mbone Engineering Issues
[email protected]
c=IN IP4 128.59.21.70
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000
INVITE
407 Needs
Auth
INVITE,
Proxy-Authorization
IP 128.59.21.70
Untrusted
DPPM v=0
sipd IN IP4 128.59.21.70
53655765 2353687637
Remove
Add o=user1
Filter
Filter
s=Mbone Audio
t=3149328700 0
(128.59.21.70,
407
INVITE
Needs
Proxy-Auth
Auth
NPUINVITE,
i=Discussion
of Mbone Engineering IssuesINVITE
[email protected]
”nonce”)
c=IN IP4 128.59.21.70
CAM
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000
RAM
(128.59.21.70,
nonce="6ydARDP51P8Ef9H4iiHmUc7iFDE=" )
May 23, 2006
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Mitigation Implementation (3)
Return-Routability Fails
Untrusted
DPPM
SIP UA
INVITE
INVITE
IP 1.2.3.4
Trusted
X
sipd
Add
Filter
INVITE
Needs
Auth
NPU 407
(1.2.3.4,”nonce”)
CAM
RAM
(1.2.3.4,
nonce="6ydARDP51P8Ef9H4iiHmUc7iFDE=" )
May 23, 2006
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Mitigation Implementation (4)
SYN Relay
TCP
Client
Syn
Relay
SYN: Seq=A
TCP
Server
SYNACK: Seq=X Ack=A+1
Generate
Random
Value X
ACK: Seq=A+1 Ack=X+1
SYN: Seq=A
Calculate
Adjustment
Y=B-X
SYNACK: Seq=B Ack=A+1
ACK: Seq=A+1 Ack=B+1
ACK: Seq=B-Y+n Ack=A+1
ACK: Seq=B+n Ack=A+1
ACK: Seq=A+p Ack=B-Y+n
ACK: Seq=A+p Ack=B+n
May 23, 2006
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Mitigation Implementation (5)
Integrated DDOS and Dynamic Pinhole filter
Linux server
ASM
sipd
CAM
DDOS
Table
FCP/UDP
CAM
SIP
DDOS
Static
Table
Inbound
Lookup
DPPM
SIP
CAM
Dynamic
Table
Switch
Outbound
Drop
May 23, 2006
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Testbed and Validation Strategy
SIPStone
 SIPStone is benchmarking tool for SIP proxy and
redirect servers
 SIPStone attempts to measure the request handling
capacity of a SIP server or a cluster of servers
 The implementation performs a series of tests that
generates a pre-configured workload
 For our project SIPStone was enhanced with:
– Null digest authentication
– Optional spoofed source IP address SIP requests
May 23, 2006
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Testbed and Validation Strategy
Methodology
 Use the SIPStone testing tool in a distributed
environment to generate SIP traffic
 Generate both spoofed and legitimate source address
requests
 Measure the following calls/sec thruput values:
–
–
–
–
Legitimate requests, without authentication (Capacity)
Legitimate requests, with authentication (Normal)
Legitimate and spoofed requests, without authentication (Attack)
Legitimate and spoofed requests, with authentication (Defense)
 Identify the impact of spoofed addresses floods on the
calls/sec rate of legitimate requests
– We should see A << N, and ideally, D = N
May 23, 2006
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Testbed Architecture
Legitimate
Loaders
(SIPStone)
GigE Switch
Attack
Loaders
(SIPStone
)
Call
Handlers
(SIPStone)
GigE Switch
Controller
(SIPStone)
SIP Proxy
May 23, 2006
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Demo
 Flood of spoofed INVITE requests
– Acquire a legitimate UA IP address
– Send a flood of spoofed INVITE requests using the UA’s IP
address
– While the firewall blocks the attacker source IP, try to send
an INVITE from the legitimate UA
 The UA’s INVITE is blocked
 Session teardown attack
– Sniff on the signaling channel
– Acquire an active session’s dialog identifiers (Call-ID, tags)
and UAs SIP URIs
– Send a spoofed BYE message
May 23, 2006
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Discussion
May 23, 2006
32
Impact of TLS on DOS
A good number of attacks identified will
be eliminated
TLS is not ready for “prime time” yet
– Few IP phone vendors are implementing
SIP over TCP, a first step towards TLS
May 23, 2006
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Conclusions
 Have demonstrated SIP vulnerabilities
 Have implemented some “carrier-class”
mitigation strategies
 Have built a validation testbed to measure
performance
 Need to generalize methodology to cover a
broader range of cases and apply anomaly
detection, pattern recognition and learning
systems
May 23, 2006
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Back up slides
May 23, 2006
CS-2000 Physical Architecture
Deep Packet Processing Module (DPPM)
 Executes Network Application Inspecting and Controlling Packet Data
 Real-Time Silicon Database (128 bits wide X 512K long) and Unstructured
Packet Processing



CAM technology
Single or Dual DPPM Configurations for HA, Performance or Multiple Use
Physical Connectivity: Gigabit Ethernet and OC-3/OC-12/OC-48 POS
Auxiliary Slots
Future use for
 HDD Module
 Telemetry Inputs/Outputs
 Optical Bypass/HA Module
Application Server Module (ASM)
 Hardened Linux Infrastructure
 Hosts Analysis Applications
 Network Element Management
(Web, CLI, SNMP, ODBC)
 Mandatory Access Control
May 23, 2006
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CS2K CALL SERVER COMPLEX
XPM
SMDI
ISM
MS/ENET
FLPP
VOICEMAIL
SS7 LINKS
STP PAIR
CALEA
PMA
IW-SPM
MS2010
SSL
SSL
BCT SESSION
SYSTEM
MAS MANAGER MANAGER
SST
SDM
COAM
(N240)
COAM
(N240)
CMT/
IEMS
MG9K
EM
XA-CORE SAM21
SIP
ERS8600
ERS8600
ERS8600
BEARER LAN
ERS8600
CS LAN
LCR
AER
AER
AER
LCR
ADM
C6509 C6509
MG15K
(PVG)
ADM
AER
GWR
C7206
SS8
OLT
C2950
SS8
GR303
S/BC S/BC
MG9K
Session Border Controllers
PON
PSTN
(CLASS 4/5
E911 TOPS AIS)
ONT
ISG2000 NETSCREEN
37
SS8
SC3100
VOICEMAIL
May 23, 2006