GTP Replay Attacks
Understanding GTP-C message replay vulnerabilities, sequence number exploitation, and anti-replay protection mechanisms in mobile core networks.
Description
A vulnerability in GTP-C message processing allows attackers to capture and replay legitimate GTP-C messages, potentially leading to unauthorized operations. The weakness stems from inadequate sequence number validation and lack of anti-replay mechanisms in many GTP implementations.
Attack Vector
Network-based attack requiring the ability to capture GTP-C traffic
Attack Complexity
Medium - Requires network access and protocol knowledge
1. Message Capture and Replay
Attackers capture legitimate GTP-C messages from the network and replay them at a later time to trigger unauthorized operations or manipulate session state.
tcpdump -i eth0 -w gtp-capture.pcap 'udp port 2123'
# Replay captured messages
tcpreplay -i eth0 gtp-capture.pcap
2. Sequence Number Exploitation
Manipulating or bypassing sequence number validation to replay messages that would otherwise be rejected by the receiving node.
- Exploiting weak sequence number validation
- Predicting sequence number patterns
- Replaying messages within acceptance windows
- Exploiting sequence number wraparound
3. Session Manipulation
Using replayed messages to manipulate subscriber sessions, including session creation, modification, or deletion operations.
- Replaying Create Session Request messages
- Duplicating Modify Bearer Request operations
- Triggering unauthorized Delete Session operations
- Manipulating handover procedures
Scenario 1: Session Duplication Attack
An attacker captures a Create Session Request and replays it to create duplicate sessions, potentially causing billing fraud or resource exhaustion.
Scenario 2: Service Disruption via Delete Session Replay
Replaying Delete Session Request messages to terminate active subscriber sessions, causing service disruption and denial of service.
Scenario 3: QoS Manipulation via Modify Bearer Replay
Replaying Modify Bearer Request messages with altered QoS parameters to gain unauthorized service upgrades or degrade competitor services.
Operational Impact
- Unauthorized session operations
- Service disruption and outages
- Resource exhaustion attacks
- Network instability
- Increased operational costs
Security Impact
- Session hijacking opportunities
- Authentication bypass potential
- Integrity compromise
- Audit trail manipulation
- Compliance violations
Business Impact
- Revenue loss from service fraud
- Billing system manipulation
- Customer dissatisfaction
- Reputation damage
- Regulatory penalties
Subscriber Impact
- Unexpected service disconnections
- Billing anomalies
- Service quality degradation
- Privacy concerns
- Loss of trust
Anti-Replay Protection
Implement robust anti-replay mechanisms to detect and reject replayed messages.
- Implement sequence number validation with sliding windows
- Use timestamps in message validation
- Maintain replay detection databases
- Implement message freshness checks
- Use cryptographic nonces for critical operations
Strong Sequence Number Management
Implement secure sequence number generation and validation mechanisms.
- Use cryptographically secure random number generators
- Implement strict sequence number validation
- Configure appropriate acceptance windows
- Monitor for sequence number anomalies
- Implement sequence number synchronization
GTP Firewall Deployment
Deploy GTP-aware firewalls with replay detection capabilities.
- Enable replay detection features
- Configure message validation rules
- Implement session state tracking
- Monitor for suspicious replay patterns
- Generate alerts for detected replay attempts
Message Authentication
Implement message authentication to prevent replay of captured messages.
- Use IPsec for GTP-C message protection
- Implement message authentication codes (MAC)
- Deploy mutual authentication between GTP peers
- Use time-based authentication tokens
- Implement certificate-based authentication
Sequence Number Monitoring
Monitor for duplicate sequence numbers, out-of-order messages, and sequence number anomalies that may indicate replay attempts.
Timing Analysis
Analyze message timing patterns to detect replayed messages that arrive outside expected time windows or with suspicious timing characteristics.
Session State Validation
Validate message consistency with current session state to detect replayed messages that conflict with established session parameters.
Behavioral Analysis
Use machine learning and behavioral analysis to identify abnormal message patterns indicative of replay attacks.