Page 46 - Digital Financial Services security assurance framework

1� Customer - mobile device f. If the application allows for the negotiation of
weak cipher suites, the application can be subject
a. Exposure of sensitive customer information due to downgrade attacks to older versions that con-
to the customer sharing the device with others, or tain potentially weak ciphers. If session keys are
having it lost, stolen, or seized or by an adversary not periodically renegotiated, the accumulation of
shoulder surfing user credentials. enciphered material can make the key vulnerable
b. Unauthorized access to the device by an attack- to attack.
er guessing the PIN or password on the device or g. Unauthorized access to lost or stolen mobile
otherwise defeating the authentication mecha- device.
nisms - if they are set up - on the mobile device. h. Mobile application tampering.
c. Tampering with the device in order to compromise
the security of the underlying platform, for exam- 3� Customer - DFS agent
ple, installing malware on the underlying storage
or extracting secrets from the device’s memory a. Customers can be vulnerable to SIM swap attacks,
through its manipulation. where the attacker represents themselves to the
d. Altering the call settings by an unauthorized mali- agent as the customer in order to gain a new SIM
cious attacker to set call and SMS forwarding, this card that provides access to the DFS account.
enables attacker get access to DFS information b. Similar vulnerabilities can be exposed against
sent through messages, like OTP. companion cards linked to DFS accounts if insuffi-
cient authentication of the customer’s credentials
2� Mobile device - mobile application is performed by the agent or if the agent is collud-
ing with the adversary.
a. Code vulnerabilities within the mobile application
can be leveraged by attackers who gain access to 4� Mobile device - Base station
the mobile device, e.g., through over-applications.
This can result in a compromise of customer data, a. Legacy GSM networks where DFS applications
loss of privacy, and loss of integrity. are primarily using SMS or USSD or IVR rely on
b. Compromise of the underlying mobile platform security provided by the network is based on GSM
can introduce viruses, trojans, worms, ransom- networks encryption algorithms such as A5/1 and
ware, and other malware/rootkits that can allow A5/2. These algorithms have been demonstrated
for the compromise of customer information, to be vulnerable. Recent work has demonstrated
or make the user more susceptible to phishing that similar approaches can be used to compro-
attempts to gain credentials for the application, mise the A5/3 cipher. In some systems, the A5/0
allowing the attacker to gain unauthorized access algorithm is specified, which provides null encryp-
to the customer account. tion and hence no protection of data confidenti-
c. Insufficient access controls within the application, ality, leading to the ability for an attacker to exfil-
e.g., an authentication mechanism required before trate sensitive information over the air interface.
sensitive operations occur (e.g., registration, pay- Regardless of the underlying transport network
ment transfer) based on assumptions about trust security threats STK and https do provide end to
can lead to application compromise and conse- end encryption.
quent exfiltration of customer data or unautho- b. Legacy networks relying on GSM encryption
rized money transfer. (STK, USSD and IVR) are also subject to “man-
d. A lack of logging/audit capabilities within the app, in-the-middle” attacks from rogue base stations
and the lack of storing such log data in a protected that are placed by an attacker, maliciously claim-
part of the device storage, can prevent guarantees ing to be legitimate provider towers (i.e., a fake
of non-repudiation and leave the user vulnerable base station, often called an “IMSI-catcher”) and
to not being able to prove that they were attacked. decrypting communication before re-sending it
e. A lack of or misuse of encryption within the appli- into the mobile carrier’s network. Such a scheme
cation such that it is written in an insecure manner can allow the attacker to gain full access to all
to application logs, or stored in databases with no communicated information, including transaction
or weak encryption can also lead to an adversary and financial data.
exposing this information.

44 Digital Financial Services Security Assurance Framework