Page 47 - Digital Financial Services security assurance framework

5� Mobile Device - Internet d. Information can be spoofed by insiders, particu-
larly in protocols that provide no notion of mes-
a. The security of the communication link is con- sage integrity.
tingent on the negotiated cipher suite between e. The increased ease of access to the SS7 network
the application and the back-end services in end- allows an attacker to use MAP(Mobile Application
to-end systems over the Internet. Information in Part) operations to insert or modify subscriber
applications has been demonstrated to flow to a data, intercept mobile communication or identify
variety of sinks outside the authorized end-point, subscriber location.
including into logs and databases. Consequently, f. The communication link between the mobile base
only strong encryption mechanisms such as TLS station and the provider network is a wireline link
ensure data security in public telecommunica- in some scenarios, while in others, depending on
tions networks. the topography of the mobile network, the base
b. It is also important to ensure that the cipher suites stations may be connected to the provider net-
used are not subject to downgrade attacks to old- work wirelessly, such as through a microwave link.
er versions that contain potentially weak ciphers. If this communication is unencrypted then, par-
If session keys are not periodically renegotiat- ticularly for SMS and USSD-based transactions
ed, the accumulation of enciphered material can where encryption is strictly provided through
make the key vulnerable to attack. Protocols such GSM algorithms between the handset and base
as SSL and transport layer security (TLS) can station, that data could potentially be sent back
be set to renegotiate ciphers, but it is important to the network in the clear, facilitating a breach of
for the protocols to be resistant to renegotiation confidentiality.
attacks from attackers injecting traffic into legit- g. In the DFS context, a bad actor with SS7 net-
imate client-server exchanges. Negotiation of work-level access can emulate (‘spoof’) the Caller
weak cipher suites that downgrade security can Line Identity (CLI) of a trusted person or entity,
allow an adversary to modify transactions and, and call the DFS customer to attempt to extract
hence, the integrity of financial data. DFS and bank credentials from the customer, ulti-
c. Without proper encryption on information pass- mately leading to financial loss.
ing through Internet connections, information can h. MNO customers can fall victim to unauthorised
be eavesdropped over the Wi-Fi link between the SIM Swaps, and attackers can leverage on sub-
mobile device and access point. Recent attacks scriber information obtained from SS7 attacks to
against key TLS key negotiation demonstrate that obtain information that can be used for success-
even strong Wi-Fi protocols such as WPA2 can ful execution of SIM swap or in collaboration with
potentially be at risk of compromise. internal personnel within the MNO.
i. Privileged users within the MNO can misuse their
6� Base station-Mobile Switching Station - access to core nodes like the HLR, and MSC to
Gateways perform activities like call and SMS transfers, call
forwarding, unauthorised interception and collec-
a. Insufficient internal controls can allow insid- tion of DFS subscriber call data records.
er access to customer data. This is particularly
important for SMS and USSD solutions that do not 7� Mobile Network - DFS operator
provide encryption within the provider network.
b. A malicious actor with access to the SS7 network a. There is often little in the way of data protection,
could send Message Transfer Part (MTP) man- particularly data encryption, once information
agement messages to fake network congestion, is transmitted into the provider network. There
reroute messages or deny service/link availability. are many reasons for this, including, primarily,
c. Mobile network are also susceptible Denial of Ser- the computational cost and overhead required
vice (DoS) threats that can be executed through to maintain encrypted high-bandwidth connec-
overloading the SS7 Links. An attacker sends a tions within the network. There is also often the
high number of SCCP (Signaling Connection Con- assumption that threats to the network primarily
trol Part) requests that require a lot of processing, arise from outside rather than within. The result is
for example translation of Global Titles. vulnerabilities exist from both insider adversaries
and outside threats that are able to penetrate the
network.

Digital Financial Services Security Assurance Framework 45