Penetration testing in the telecom world isn’t your average port scan and exploit script routine. When it comes to SS7, Diameter, and GTP protocols, the stakes are higher, the attack surface is vast, and the vulnerabilities—when exploited—can have catastrophic consequences for operators and users alike. These protocols were not designed with modern security in mind, making them prime targets for telecom-specific offensive security testing.
In this article, we’ll dive deep into how penetration testing is performed on these protocols, why it's critical for mobile network operators (MNOs), and what unique tools, techniques, and mindsets are required to get it right.
Why Focus on SS7, Diameter & GTP?
SS7 (Signaling System 7)
Used in 2G and 3G networks, SS7 underpins international roaming, SMS delivery, call setup, and subscriber data access. Designed in a pre-threat era, it lacks built-in authentication and encryption. This makes it vulnerable to location tracking, SMS interception, fraud, and subscriber data exfiltration.
Diameter
Diameter is the successor to SS7 for 4G/LTE networks and plays a core role in policy control, authentication, and charging. While more secure on paper, its complexity and lack of segmentation across real-world deployments introduce serious security flaws—especially when interacting with legacy SS7 systems or external roaming partners.
GTP (GPRS Tunneling Protocol)
GTP is the backbone of user data transport, especially across 3G, 4G, and 5G NSA (Non-Standalone) cores. Vulnerabilities in GTP can lead to user impersonation, billing fraud, DoS attacks, and data leakage.
How Penetration Testing Works for These Protocols
Penetration testing for mobile core protocols requires far more than scanning IPs and looking for open ports. These are stateful protocols with complex dialogues, meaning effective testing mimics the behavior of legitimate network elements.
Step 1: Intelligence Gathering
- Identifying exposed STPs (for SS7), Diameter Agents, or GGSNs/S-GWs.
- Mapping interconnect partners and roaming paths.
- Performing passive monitoring when possible to fingerprint services.
Step 2: Protocol Fuzzing & Injection
- Using telecom-specific fuzzers to manipulate messages like SRI-SM, Update Location, or Create Session Requests.
- Testing enforcement of policies and security filters.
Step 3: Abuse Scenarios & Exploit Chains
- Location tracking via MAP ProvideSubscriberInfo (SS7).
- SMS interception via MAP SendRoutingInfoForSM.
- Fraud via GTP-U spoofing or injection.
- Authentication bypass or downgrade via malformed Diameter AVPs.
Step 4: Lateral Movement and Persistence
- Exploiting peering misconfigurations.
- Discovering ways to pivot through insecure interconnects.
Step 5: Reporting with Telecom Context
- Unlike standard PT reports, telecom penetration testing must tie findings to GSMA FS.11, IR.82, 3GPP TS 29.060, and other industry standards.
- Risk levels must be assessed not just in CVSS scores, but in terms of impact on network integrity, subscriber privacy, and billing systems.
Tools of the Trade (and Why Generic Ones Don’t Cut It)
Generic pentesting tools like Metasploit or Burp Suite don’t help here. Instead, offensive telecom testing relies on specialized tools, including:
- PTA (P1 Telecom Auditor): A full-featured testing framework for SS7, Diameter, and GTP.
- Protocol Simulators: Emulating MME, SGW, or HSS behavior for testing.
- Vulnerability Knowledge Bases (VKB): Including live CVEs, configurations, and abuse patterns specific to telecoms.
- Custom-built fuzzers for MAP, CAP, AVP encoding, and GTP-U manipulation.
The Business Case for Telecom Penetration Testing
Penetration testing for SS7, Diameter, and GTP isn’t a nice-to-have—it's a compliance requirement and strategic necessity:
- Regulatory Compliance: Frameworks like NIS2, CRA, and national security agencies demand periodic offensive testing.
- Risk Mitigation: Avoid reputational damage from high-profile incidents (e.g., SS7-based bank fraud or GTP-based DoS).
- Supply Chain Assurance: With interconnected systems and vendors, operators must validate every trust boundary.
- Network Transformation Projects: 5G rollouts, virtualization, and cloudification expose old weaknesses in new places.
Final Thoughts: Offensive Security is Not Optional
SS7, Diameter, and GTP may sound like niche protocols to outsiders, but they are the lifeblood of global connectivity. Penetration testing these protocols requires deep telecom fluency, not just generalist cyber skills. Mobile operators must adopt offensive telecom security as a proactive defense—before adversaries do it for them.
At P1 Security, we’ve spent over a decade developing purpose-built tools, training, and testing methodologies tailored to these exact challenges. Because in mobile networks, real security starts with deep protocol awareness—and a willingness to break things before attackers do.
