How to Use Packet Injectors for SS7 Red Team Security Testing
Packet injectors help security teams examine how signalling infrastructure reacts to carefully controlled SS7 and SIGTRAN traffic. Used properly, they can reveal weaknesses in message validation, routing controls, timer handling, monitoring, and failover behaviour without placing live subscribers or emergency services at risk.
For Australian operators and enterprise telecoms teams, this work should be performed under written authorisation and within a lab or approved maintenance window. Legacy SS7 interconnects may still support mobile, fixed-line, roaming, and messaging services across networks operated by Telstra, Optus, and Vodafone, so a casual test on production links is not acceptable.
Define The Red Team Scope
Begin with a written rules-of-engagement document. It should identify signalling points, point codes, Global Titles, SIGTRAN associations, test numbers, permitted message types, rate limits, and the exact systems that may receive traffic. Include stop conditions for abnormal CPU use, queue growth, SCTP association loss, or unexpected subscriber impact.
The scope should cover the security questions being tested rather than simply listing tools. Examples include whether an STP rejects an invalid route, whether an SMS firewall detects unusual MAP activity, and whether monitoring creates a useful alert when a message arrives from an unauthorised peer.
Australian testing may also involve privacy obligations under the Privacy Act and operational expectations from the Australian Communications and Media Authority. Keep test data synthetic, avoid real customer identifiers, and coordinate carefully with a network operations centre, especially when systems carry traffic between Sydney, Melbourne, Perth, and regional sites.
Build An Isolated Test Lab
A useful lab can contain an STP or signalling gateway, an M3UA/SCTP stack, a packet injector, a capture sensor, and a log collection platform. Replicate the relevant layers: SCTP transport, M3UA adaptation, MTP3 routing, SCCP addressing, and selected ISUP or MAP procedures.
Use private point codes and test Global Titles that cannot be routed externally. Firewall every interface, disable unnecessary peering, and place the injector behind a management network. If cloud infrastructure is used, confirm that security groups and routing tables prevent accidental reachability to carrier networks.
Traffic captures should be synchronised with application and system logs. Network Time Protocol is important because a few seconds of clock drift can make it difficult to correlate an injected message with an STP decision or an alarm.
Select And Configure The Injector
A packet injector may be a commercial signalling test platform, a SIGTRAN protocol tester, or a programmable framework such as Scapy extended for the required layers. Select a tool that can construct valid SCTP, M3UA, MTP3, SCCP, ISUP, or MAP messages while allowing controlled changes to addressing, sequence values, timers, and message rates.
Start with protocol-conformant traffic. A valid message gives the test team a baseline for normal routing and response behaviour. Then alter one field at a time, such as an unknown point code, an unexpected service indicator, an unsupported message type, or a deliberately delayed response.
Do not begin with high-volume flooding. Set a low packet-per-second limit, use a bounded replay file, and add an immediate stop control. The objective is to evaluate defensive logic, not to recreate an outage. Training on signalling architecture and protocol relationships can be supported by these SS7 training materials before tools are connected to the lab.
Design Safe Test Cases
A strong test case states its purpose, input, expected response, evidence source, and rollback step. For example, an invalid MTP3 destination should be rejected or routed to a defined failure path, while the monitoring system should record the event with enough detail for investigation.
Cover both malformed and unusual-but-valid traffic. Useful categories include route management, SCCP address handling, ISUP call-state transitions, MAP procedure controls, duplicate messages, timer expiry, and unexpected peer behaviour. Test rate limiting separately from message validation so the results remain clear.
Include negative tests for authentication and trust boundaries between signalling peers. A lab gateway should reject unauthorised source addresses and unsuitable point codes. Where a test imitates roaming or inter-carrier traffic, use fictional subscriber references and document every assumption.
Observe Routing And Failover
Packet captures show what was sent, but they do not always explain why a network made a decision. Collect STP route tables, M3UA state changes, SCTP association events, firewall records, application logs, and alerts from security monitoring platforms.
Pay close attention to timers and recovery paths. A route may appear unavailable because of linkset failure, congestion, destination restrictions, or an expired signalling association. The MTP3 recovery guide provides useful background for distinguishing these conditions during analysis.
Australian geography can make failover results less predictable. A backup path between eastern capitals may behave differently from a link serving Western Australia or a remote regional exchange. Measure recovery time, message loss, duplicate delivery, and alarm quality rather than assuming that a nominally redundant route performs identically.
Compare Injector Approaches
The right platform depends on whether the engagement values repeatability, protocol depth, flexibility, or operational simplicity. A programmable injector is useful for custom cases, while a commercial platform may provide stronger reporting and safer controls for a carrier environment.
| Approach | Best Use | Strengths | Limitations |
|---|---|---|---|
| Commercial SS7 tester | Formal operator assessment | Broad protocol coverage, support, reporting | Higher cost and licensing |
| SIGTRAN protocol tool | M3UA and SCTP validation | Repeatable association and transport tests | May need extra SCCP or MAP capability |
| Programmable packet framework | Custom research in a lab | Flexible fields, automation, scripting | Requires protocol expertise and careful safeguards |
| PCAP replay utility | Regression testing | Fast, consistent reproduction | Limited variation unless captures are edited |
Whichever method is selected, preserve the original test configuration and packet set. Reproducibility matters when a carrier, vendor, or internal operations team needs to verify a finding months later.
Report Findings And Retain Evidence
A useful report links each observation to a security impact. Describe the affected protocol layer, the injected condition, the device response, the alert or missing alert, and the recovery result. Avoid vague statements such as “SS7 is insecure”; identify the specific control that failed or worked as intended.
Evidence should include sanitised packet captures, timestamps, route states, screenshots of alerts, configuration references, and a short reproduction procedure. Record whether the result was observed on a lab replica, a pre-production environment, or an authorised live test window.
Checks Before Sending Traffic
- Confirm written permission and named technical contacts
- Verify private point codes and non-routable test identities
- Set packet, session, and duration limits
- Test the emergency stop before the first run
Evidence To Capture
- Injector configuration and software version
- SCTP, M3UA, and signalling-layer packet traces
- STP, firewall, and application log entries
- Recovery time, alarms, and operator actions
The most reliable use of packet injectors is measured, repeatable, and isolated. Treat every signalling message as an operational event, validate one control at a time, and remember that a successful SS7 red team exercise is judged by safe evidence and improved detection—not by how much traffic the network can endure.
