S6a Interface Information Disclosure

High Risk

4G Networks

Diameter Protocol

Attack Vector Overview

S6a Interface Information Disclosure attacks exploit vulnerabilities in the Diameter S6a interface between the MME and HSS to extract sensitive subscriber information without proper authorization.

Technical Details

How S6a Interface Information Disclosure attacks work

The S6a interface in 4G/LTE networks connects the Mobility Management Entity (MME) to the Home Subscriber Server (HSS) and is used for authentication, authorization, and subscriber profile management. Information disclosure attacks target this interface to extract sensitive subscriber data.

Attack Methodology

Network Reconnaissance: Attackers first identify the S6a interface endpoints and Diameter nodes in the target network.
Diameter Node Impersonation: The attacker impersonates a legitimate MME by spoofing its Diameter identity.
Authentication Information Requests: The attacker sends Authentication Information Request (AIR) messages to the HSS to retrieve authentication vectors.
Update Location Requests: The attacker sends Update Location Request (ULR) messages to retrieve subscriber profiles.
Data Extraction: The attacker extracts IMSI, authentication keys, service profiles, and other sensitive information from the responses.

Figure 1: S6a Interface Information Disclosure Attack Flow

Example Attack Scenario

1. Attacker sends AIR message with spoofed Origin-Host and Origin-Realm:

<diameter version="1.0">
  <header command_code="318" application_id="16777251" flags="request">
    <origin host="fake-mme.operator.com" realm="operator.com" />
    <destination host="hss.operator.com" realm="operator.com" />
  </header>
  <avp code="1" name="User-Name" value="234150999999999" />
  <avp code="10415:1032" name="RAT-Type" value="1004" />
  <avp code="10415:1408" name="Visited-PLMN-Id" value="23415" />
</diameter>

2. HSS responds with authentication vectors:

<diameter version="1.0">
  <header command_code="318" application_id="16777251" flags="response">
    <origin host="hss.operator.com" realm="operator.com" />
    <destination host="fake-mme.operator.com" realm="operator.com" />
  </header>
  <avp code="10415:1413" name="Authentication-Info">
    <avp code="10415:1414" name="E-UTRAN-Vector">
      <avp code="10415:1417" name="RAND" value="..." />
      <avp code="10415:1418" name="XRES" value="..." />
      <avp code="10415:1416" name="AUTN" value="..." />
      <avp code="10415:1415" name="KASME" value="..." />
    </avp>
  </avp>
</diameter>

Impact Assessment

S6a Interface Information Disclosure attacks can have severe consequences for both subscribers and mobile network operators:

Subscriber Privacy Breach

Exposure of subscriber identities (IMSI)
Disclosure of subscriber location information
Leakage of subscription profiles and service details

Security Compromise

Theft of authentication vectors
Potential for subsequent authentication bypass
Enablement of IMSI-catcher attacks

Regulatory Implications

Violation of data protection regulations
Potential for significant financial penalties
Mandatory breach notifications

Operational Impact

Loss of subscriber trust
Potential for service disruption
Increased operational costs for incident response

Risk Factors

The risk is particularly high for operators who have not implemented proper Diameter security controls or who rely on legacy equipment with limited security capabilities.

Detection & Mitigation

Detection Methods

Detecting S6a Interface Information Disclosure attacks requires monitoring Diameter signaling traffic and implementing anomaly detection systems:

Diameter Signaling Monitoring: Implement continuous monitoring of Diameter signaling traffic, focusing on S6a interface messages.
Origin-Host Verification: Check for inconsistencies between the Origin-Host AVP and the actual source of Diameter messages.
Behavioral Analysis: Monitor for unusual patterns in AIR and ULR message frequency or volume from specific nodes.
Subscriber Activity Correlation: Correlate Diameter signaling with actual subscriber activity to identify unauthorized queries.
Security Information and Event Management (SIEM): Integrate Diameter signaling logs with SIEM systems for correlation and alerting.

Key Indicators of Compromise

Unexpected AIR/ULR messages from unknown or suspicious Diameter nodes
Mismatches between Origin-Host AVP and actual message source
High volume of subscriber data queries from a single node
Queries for subscribers from unexpected serving networks
Authentication requests without subsequent attach procedures

Related Attack Vectors

Standards & References

3GPP TS 29.272Evolved Packet System (EPS); Mobility Management Entity (MME) and Serving GPRS Support Node (SGSN) related interfaces based on Diameter protocol
RFC 6733Diameter Base Protocol
GSMA FS.19Diameter Interconnection Security
ENISA Technical GuidelineSecurity measures for Diameter signaling

Tools & Resources

1
Diameter EPC Testing FrameworkOpen-source tool for testing Diameter interfaces in EPC networks
2
Wireshark with Diameter DissectorNetwork protocol analyzer with Diameter protocol support
3
Diameter Security ScannerSpecialized tool for identifying vulnerabilities in Diameter implementations