4G - Who is paying your cellular phone bill?

Cellular networks are connected with each other through a worldwide private, but not unaccessible network, called IPX network. Through this network user related information is exchanged for roaming purposes or for cross-network communication. This private network has been breached by criminals and nation states. Cellular networks are extremely complex and many attacks have been already been found e.g. DoS, location tracking, SMS interception, data interception. Many attacks have been seen in practice, but not all attack are understood and not all attack avenues using the IPX network have been explored. This presentation shows how a S9 interface in 4G networks, which is used for charging related user information exchange between operators can be exploited to perform fraud attacks. A demonstration with technical details will be given and guidance on practical countermeasures.


  • Dr. Silke Holtmanns, Distinguished Member of Technical Staff, Security Expert, Nokia Bell Labs
  • Isha Singh, Master student, Aalto University in Helsinki (Finland)

Dr. Silke Holtmanns
Silke is a security expert at Nokia Bell Labs (Research branch of Nokia). She holds a PhD in Mathematics and has 18 years of experience in mobile security research and standardization. In her current research she investigates new and existing mobile network security attacks using SS7, Diameter and GTP protocols via the interconnection network and how to counter those attacks in 4G/5G networks. She found many 4G related IPX attacks and countermeasures e.g. Location Tracking (NATO CyCon), DoS (Black Hat EU 2016), cellular data interception (34C3 Chaos Computer Congress). She drives in the operator association GSMA the security of cellular network and being responsible there for the Diameter Signaling Security Specification. She served as a special matter expert on cellular security to the US Federal Communication Commission and to the European Union Agency for Network and Information Security. She is rapporteur of ten 3GPP security specifications and has a long track record of security publications.

Currently, she is actively supporting the 5G Roaming security developments. For her the interesting part is fixing problems in world wide network without breaking it, not finding an issue.


Isha Singh
Isha is a master student at Aalto University in Helsinki (Finland) and doing her Thesis research work at Nokia Bell Labs under supervision of Professor Raimo Kantola. She is completing her Master's in Wireless Communication as major subject and Machine Learning as minor. Her research covers smart city environmental perception from ambient cellular signals and 5G Ubiquitous sensing. She is passionate about IoT devices and their security in 5G scenario. She has experiences on embedded devices (Arduino, Raspberry Pi) for multiple projects like Analog to Digital converter used in optical communication. Presently she is exploring Cybersecurity, starting from the mobile communication core network security. Testing for vulnerabilities and loopholes and providing solutions using Machine Learning.

Detailed Presentation:

(Source: DEF CON 26)
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