SS7 Security Audit for Open Point Code Access
An SS7 security audit examines whether external or unauthorized network elements can reach signaling destinations that should remain restricted. Open point code access is a particularly important finding because it may expose routing functions, subscriber-related signaling, or interconnect resources to misuse.
Point codes identify signaling nodes within MTP3 and related SS7 networks. When access controls are weak, an attacker or improperly configured partner may send traffic toward an STP, HLR, MSC, SMSC, or service control point without appropriate screening. The risk increases when traditional SS7 signaling is carried over SIGTRAN and IP-based transport.
A practical review combines configuration analysis, controlled signaling tests, routing verification, and evidence from firewalls, STPs, signaling gateways, and monitoring platforms. The goal is to confirm which point codes are reachable, why they are reachable, and whether each permitted route has a documented business purpose.
Audit Scope and Objectives
Begin by defining the signaling domains under review. Include national and international point codes, adjacent signaling points, STP clusters, SIGTRAN associations, SCTP endpoints, signaling firewalls, and connections to IPX or roaming partners. Record whether each link uses MTP2, M2PA, M2UA, SUA, or another transport arrangement.
The audit should answer several practical questions. Can an untrusted source address an internal point code? Can a partner reach destinations outside its assigned scope? Are point-code ranges filtered consistently across primary and backup paths? Can traffic bypass the signaling firewall through a legacy SS7 link, management interface, or alternate SIGTRAN association?
Establish an evidence standard before testing. Configuration exports, packet captures, route tables, access-control lists, change records, and alarm logs should support every finding. Testing must use authorization, controlled test numbers, and rate limits so that verification does not affect live call routing or subscriber services.
Map the Signaling Exposure
Create a current signaling inventory rather than relying on network diagrams alone. For each node, document the point code, network indicator, role, transport address, connected peer, supported SS7 protocols, and permitted message classes. Include global title translation rules because a seemingly restricted point code may still be reachable through an unrestricted SCCP translation path.
Review MTP3 routing tables for broad entries, default routes, and unexpected neighboring relationships. A route that accepts an entire point-code range may be operationally convenient but provide excessive reachability. Pay special attention to routes learned or maintained through redundant STPs, where one device may enforce screening while its partner does not.
For SIGTRAN, compare SCTP association endpoints with the logical signaling topology. An association should not automatically grant access to every point code behind a signaling gateway. Validate source IP restrictions, association authentication, VLAN separation, and the relationship between IP-layer policy and MTP3 or SCCP screening.
Validate Access Controls
Point-code access should be based on explicit allow rules, least privilege, and direction-specific policy. A roaming partner may need access to selected MAP procedures through a defined signaling firewall policy, while an internal application gateway may require only a narrow set of destinations and operations.
Inspect ACLs and screening rules for permissive entries such as “any source,” broad point-code ranges, unrestricted network indicators, and rules that allow all SCCP message types. Check whether rules distinguish between originating and destination point codes, global titles, subsystem numbers, and protocol operations.
The following comparison helps organize evidence during a review:
| Control area | Secure condition | Warning sign | Evidence to collect |
|---|---|---|---|
| MTP3 routing | Specific destinations and approved neighbors | Default or broad point-code routes | Route tables and change records |
| SCCP screening | GT, SSN, and message restrictions | Unfiltered global title translation | Translation rules and test captures |
| SIGTRAN transport | Restricted peers with authenticated associations | Open SCTP exposure or shared segments | Firewall and SCTP configurations |
| Signaling firewall | Directional, logged allow rules | Any-to-any signaling policy | Policy export and event logs |
| Monitoring | Alerts for abnormal point-code activity | No visibility into rejected traffic | SIEM records and alarm history |
A useful audit also checks whether denied traffic is genuinely rejected. Some platforms log a rule match but continue processing through a secondary route. Capture signaling at multiple points to verify that a blocked request does not reappear through an alternate STP, gateway, or IP interconnect.
Test Routes and Abuse Paths
Controlled testing should confirm reachability without generating harmful traffic. From an approved test source, send carefully selected signaling messages toward authorized and unauthorized point codes. Measure whether the message is rejected at the IP layer, signaling firewall, MTP3 layer, SCCP layer, or application protocol layer.
Test both direct and indirect paths. An inaccessible point code may become reachable through a global title, a translated subsystem number, a backup STP, or a partner route. Review responses and error causes for information leakage, including whether the network reveals node existence, supported services, or routing details to an untrusted source.
Include negative tests for MAP, ISUP, and SCCP where appropriate. A partner permitted to perform roaming-related procedures should not automatically be able to initiate unrelated subscriber queries, send unauthorized SMS signaling, or access call-control functions. Rate limits and anomaly controls should also be tested for effectiveness.
For organizations assessing broader exposure, SS7 security solutions can provide useful context for linking protocol-level findings with signaling protection and operational controls.
Interpret Findings by Risk
An open route to a noncritical test node is different from unrestricted access to a production HLR or SMSC. Classify findings according to reachable asset, permitted operation, source trust, exploitability, monitoring coverage, and potential effect on confidentiality, integrity, and service availability.
High-risk findings commonly include external access to sensitive point codes, unrestricted SCCP translation, missing signaling firewall enforcement, and SIGTRAN associations exposed beyond approved peers. A lower-risk issue may still require correction when it creates an undocumented route or weakens the consistency of a redundant signaling environment.
Document each result with source point code or IP address, destination, protocol layer, message type, timestamp, policy decision, and expected behavior. This level of detail allows network engineers to reproduce the issue and prevents vague findings such as “SS7 is exposed” from delaying remediation.
Prioritize Remediation Actions
Remediation should remove unnecessary reachability before adding complex detection logic. Apply explicit allowlists, narrow point-code ranges, restrict global title translation, and separate partner policies from internal network policies. Ensure that both active and standby signaling platforms use the same rule set.
Recommended actions include:
- Remove default and wildcard point-code routes from external signaling contexts.
- Restrict SCTP associations to approved addresses, interfaces, and signaling gateways.
- Enforce SCCP screening for global titles, subsystem numbers, and message categories.
- Log accepted and rejected signaling with enough detail for investigation.
- Re-test every change through direct, translated, redundant, and failover paths.
Change control is essential because signaling policies can affect roaming, emergency services, SMS delivery, and call establishment. Schedule changes with rollback procedures, validate alarms after deployment, and retain before-and-after configuration evidence.
Maintain Continuous Point-Code Governance
An audit is a snapshot unless routing ownership and monitoring continue afterward. Assign an owner for every point code and signaling relationship, and require formal approval for new destinations, partner links, translation rules, and SIGTRAN associations. Reconcile the inventory against live route tables and firewall objects on a regular schedule.
Use monitoring to detect unexpected point-code activity, rejected message spikes, new SCTP peers, abnormal global title patterns, and signaling from retired partners. Correlate these events with maintenance windows and interconnect records so that legitimate changes are distinguishable from probing or abuse.
Treat open point code access as a network boundary failure, not merely a routing error. Authorized teams should complete the exposure inventory, verify controls with safe tests, close unnecessary paths, and preserve the evidence needed to demonstrate that SS7 and SIGTRAN signaling are reachable only through approved, monitored routes.
