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Practical Security Testing for LTE Networks BlackHat Abu Dhabi December 2012 Martyn Ruks & Nils
1 06/11/2012
Today’s Talk
• Intro to LTE Networks
• Technical Details
• Attacks and Testing
• Defences
• Conclusions
06/11/2012 2
06/11/2012 3
Intro to LTE Networks
A Brief History Lesson
• 1G – 1980s Analogue technology (AMPS, TACS)
• 2G – 1990s Move to digital (GSM,GPRS,EDGE)
• 3G – 2000s Improved data services (UMTS, HSPA)
• 4G – 2010s High bandwidth data (LTE Advanced)
06/11/2012 4
Mobile Networks
Historic Vulnerabilities
• Older networks have been the subject of practical and theoretical attacks
• Examples include:
• Ability to man in the middle
• No perfect forward secrecy
• No encryption on the back-end
• LTE Advanced addresses previous attacks
06/11/2012 5
Mobile Networks
Why is LTE Important?
• We have lived with 3G for a long time
• 4G provides high speed mobile data services for customers
• High level of scalability on the back-end for operators
06/11/2012 6
Mobile Networks
06/11/2012 7
Technical Details
06/11/2012 8
NodeB Core
Network
Internet Base Station User Back-End
Conceptual View 3G
RNC
06/11/2012 9
Network Overview 3G
UE
NB
NB SGSN GGSN Internet
HSS AuC
Core Network
RNC
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eNodeB
EPC
Internet Base Station User Back-End
Conceptual View 4G
06/11/2012 11
Network Overview 4G
UE
eNB
eNB
MME
SGw PGw PCRF Internet
HSS
EPC
06/11/2012 12
The Components
UE
eNB
eNB
MME
SGw PGw PCRF Internet
HSS
EPC
User Equipment (UE)
• What the customer uses to connect
• Mainly dongles and hubs at present
• Smartphones and tablets will follow (already lots in US)
06/11/2012 13
The Components
06/11/2012 14
The Components
UE
eNB
eNB
MME
SGw PGw PCRF Internet
HSS
EPC
evolved Node B (eNB)
• The bridge between wired and wireless networks
• Forwards signalling traffic to the MME
• Passes data traffic to the PDN/Serving Gateway
06/11/2012 15
The Components
06/11/2012 16
The Components
UE
eNB
eNB
MME
SGw PGw PCRF Internet
HSS
EPC
Evolved Packet Core (EPC)
• The back-end core network
• Manages access to data services
• Uses IP for all communications
• Divided into several components
06/11/2012 17
The Components
06/11/2012 18
The Components
UE
eNB
eNB
MME
SGw PGw PCRF Internet
HSS
EPC
Mobile Management Entity (MME)
• Termination point for UE Signalling
• Handles authentication
events
• Key component in back-end communications
06/11/2012 19
The Components
06/11/2012 20
The Components
UE
eNB
eNB
MME
SGw PGw PCRF Internet
HSS
EPC
Home Subscriber Service (HSS)
• Contains a user’s subscription data (profile)
• Typically includes the Authentication Centre (AuC)
• Where key material is stored
06/11/2012 21
The Components
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The Components
UE
eNB
eNB
MME
SGw PGw PCRF Internet
HSS
EPC
PDN and Serving Gateways (PGw and SGw)
• Handles data traffic from UE
• Can be consolidated into a
single device
• Responsible for traffic routing
within the back-end
• Implements important filtering controls
06/11/2012 23
The Components
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The Components
UE
eNB
eNB
MME
SGw PGw PCRF Internet
HSS
EPC
Policy Charging and Rules Function (PCRF)
• Does what it says on the tin
• Integrated into the network core
• Allows operator to perform bandwidth shaping
06/11/2012 25
The Components
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The Components
UE HeNB MME
SGw PGw PCRF Internet
HSS
EPC
Home eNB (HeNB)
• The “FemtoCell” of LTE
• An eNodeB within your home
• Talks to the MME and PDN/Serving Gateway
• Expected to arrive much later in 4G rollout
06/11/2012 27
The Components
06/11/2012 28
Control and User Planes
Network Overview
06/11/2012 29
The Protocols
UE
eNB
eNB
MME
SGw PGw PCRF Internet
HSS
EPC
Radio Protocols (RRC, PDCP, RLC)
• These all terminate at the eNodeB
• RRC is only used on the control plane
• Wireless user and control data
is encrypted (some exceptions)
• Signalling data can also be encrypted end-to-end
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RRC
PDCP
RLC
The Protocols
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The Protocols
UE
eNB
eNB
MME
SGw PGw PCRF Internet
HSS
EPC
Internet Protocol (IP)
• Used by all back-end comms
• All user data uses it
• Supports both IPv4 and IPv6
• Important to get routing and filtering correct
• Common UDP and TCP services in use
06/11/2012 32
The Protocols
IP
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The Protocols
UE
eNB
eNB
MME
SGw PGw PCRF Internet
HSS
EPC
The Protocols - SCTP
• Another protocol on top of IP
• Robust session handling
• Bi-directional sessions
• Sequence numbers very important
06/11/2012 34
The Protocols
IP
SCTP
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The Protocols
UE
eNB
eNB
MME
SGw PGw PCRF Internet
HSS
EPC
The Protocols – GTP-U
• Runs on top of UDP and IP
• One of two variants of GTP used in LTE
• This transports user IP data
• Pair of sessions are used identified by Tunnel-ID
06/11/2012 36
The Protocols
IP
GTP-U
UDP
06/11/2012 37
The Protocols
UE
eNB
eNB
MME
SGw PGw PCRF Internet
HSS
EPC
The Protocols – GTP-C
• Runs on top of UDP and IP
• The other variant of GTP used in LTE
• Used for back-end data
• Should not be used by the MME in pure 4G
06/11/2012 38
The Protocols
IP
GTP-C
UDP
06/11/2012 39
The Protocols
UE
eNB
eNB
MME
SGw PGw PCRF Internet
HSS
EPC
S1AP
• Runs on top of SCTP and IP
• An ASN.1 protocol
• Transports UE signalling
• UE sessions distinguished by a pair of IDs
06/11/2012 40
The Protocols
IP
S1AP
SCTP
06/11/2012 41
The Protocols
UE
eNB
eNB
MME
SGw PGw PCRF Internet
HSS
EPC
X2AP
• Very similar to S1AP
• Used between eNodeBs for signalling and handovers
• Runs over of SCTP and IP and is also an ASN.1 protocol
06/11/2012 42
The Protocols
IP
X2AP
SCTP
06/11/2012 43
Potential Attacks
What Attacks are Possible
• Wireless attacks and the baseband
• Attacking the EPC from UE
• Attacking other UE
• Plugging into the Back-end
• Physical attacks (HeNB)
06/11/2012 44
Targets for Testing
Wireless Attacks and the Baseband
• A DIY kit for attacking wireless protocols is now closer (USRP based)
• Best chance is using commercial
kit to get a head-start
• Not the easiest thing to attack
06/11/2012 45
Targets for Testing
Attacking the EPC from UE
• Everything in the back-end is IP
• You pay someone to give you IP access to the environment
• Easiest place to start
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Targets for Testing
Attacking other UE
• Other wirelessly connected devices are close
• May be less protection if seen as a local network
• The gateway may enforce segregation between UE
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Targets for Testing
Wired network attacks
• eNodeBs will be in public locations
• They need visibility of components in the EPC
• Very easy to communicate with an IP network
• Everything is potentially in scope
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Targets for Testing
Physical Attacks (eNB)
• Plugging into management interfaces is most likely attack, except …
• A Home eNodeB is a different story
• Hopefully we have learned from the Vodafone Femto-Cell Attack
06/11/2012 49
Targets for Testing
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What you can Test
As a Wirelessly Connected User
• Visibility of the back-end from UE
• Visibility of other UEs
• Testing controls enforced by Gateway
• Spoofed source addresses
• GTP Encapsulation (Control and User)
06/11/2012 51
Tests to Run
From the Back-End
• Ability to attack MME (signalling)
• Robustness of stacks (eg SCTP) • Fuzzing
• Sequence number generation
• Testing management interfaces • Web consoles
• SSH
• Proprietary protocols
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Tests to Run
Challenges
• Spoofing UE authentication is difficult
• Messing with radio layers is hard
• ASN.1 protocols are a pain
• Injecting into SCTP is tough
• Easy to break back-end communications
06/11/2012 53
Tests to Run
S1AP Protocol
• By default no authentication to the service
• Contains eNodeB data and UE Signalling
• UE Signalling can make use of encryption and integrity checking
• If no UE encryption is used attacks against connected handsets become possible
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Tests to Run
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Tests to Run
eNB UE MME
S1AP NAS
NAS
S1AP and Signalling
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Tests to Run
eNB UE
MME
S1AP and Signalling
Spoofed UE
Spoofed eNB
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Tests to Run
eNB MME
S1AP and Signalling
S1 Setup
S1 Setup Response
Attach Request
Authentication Request
Authentication Response
Security Mode
GTP Protocol
• Gateway can handle multiple encapsulations
• It uses UDP so easy to have fun with
• The gateway needs to enforce a number of controls that stop attacks
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Tests to Run
GTP and User Data
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Tests to Run
eNB UE SGw
GTP IP
IP
Internet
IP
GTP and User Data
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Tests to Run
UE
IP
UDP
GTP
IP
IP
UDP
GTP
eNodeB
GTP and User Data
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Tests to Run
eNB UE SGw Internet
IP GTP
GTP IP GTP
IP GTP
GTP and User Data
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Tests to Run
eNB UE SGw
Source IP Address (IP)
Invalid IP Protocols (IP)
GTP Tunnel ID (GTP)
Source IP Address (GTP)
Destination IP Address (IP)
PGw
Old Skool
• Everything you already know can be applied to testing the back-end
• Its an IP network and has routers and switches
• There are management services running
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Tests to Run
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Defences
The Multi-Layered Approach
• Get the IP network design right
• Protect the IP traffic in transit
• Enforce controls in the Gateway
• Ensure UE and HeNBs are secure
• Monitoring and Response
• Testing
06/11/2012 65
Defences
Unified/Consolidated Gateway
• The “Gateway” enforces some very important controls:
• Anti-spoofing
• Encapsulation protection
• Device to device Routing
• Billing and charging of users
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Defences
IP Routing
• Architecture design and routing in the core is complex
• Getting it right is critical to security
• We have seen issues with this
• This must be tested before an environment is deployed
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Defences
IPSec
• If correctly implemented will provide Confidentiality and Integrity protection
• Can also provide authentication between components
• Keeping the keys secure is not trivial and not tested
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Defences
Architecture Consideration
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EPC
Internet
eNodeB
MME HSS
Serving Gateway PDN Gateway
Internet
Gateway
EPC Switch
Defences
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Conclusions
• There are 3 key protective controls that should be tested within LTE environments
• Policies and rules in the Unified/Consolidated Gateway
• The implementation of IPSec between all back-end components
• A back-end IP network with well-designed routing and filtering
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Conclusion 1
• Despite fears from the use of IP in 4G, LTE will improve security if implemented correctly
• The 3 key controls must be correctly implemented
• Testing must be completed for validation
• Continued scrutiny is required
• Legacy systems may be the weakest link
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Conclusion 2
• Protecting key material used for IPSec is not trivial
• The security model for IPSec needs careful consideration
• Operational security processes are also important
• Home eNodeB security is a challenge
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Conclusion 3
• More air interface testing is needed
• Will need co-operation from vendors/operators
• “Open” testing tools will need significant development effort
• Still lower hanging fruit if support for legacy wireless standards remain
06/11/2012 74
Conclusion 4
06/11/2012 75
Questions
@mwrinfosecurity @mwrlabs
