SS7 Service Disruption Attacks
Attacks aimed at disrupting subscriber services
SS7 service disruption attacks exploit vulnerabilities in the Signaling System No. 7 protocol to deny service to targeted subscribers. These attacks manipulate subscriber data in network databases or send fraudulent messages that cause the network to disconnect subscribers or prevent them from accessing services. Unlike other SS7 attacks that focus on surveillance or interception, service disruption attacks are primarily aimed at causing denial of service.
Security Implications
- Targeted denial of service against specific subscribers
- Disruption of critical communications during emergencies
- Business disruption for high-value targets
- Potential for large-scale service outages
- Facilitation of other attacks by preventing notifications
- Reputational damage to network operators
Technical Prerequisites
- Access to SS7 network (direct or via compromised operator)
- Knowledge of target's MSISDN (phone number) and/or IMSI
- SS7 message crafting capabilities
- Global Title (GT) spoofing ability
- Understanding of HLR/VLR operations
- Knowledge of subscriber data management operations
Service Disruption Techniques
Technical Details
The CancelLocation (CL) MAP operation is legitimately used when a subscriber moves to a new location and registers with a new VLR. The new VLR sends an UpdateLocation to the HLR, which then sends CancelLocation to the old VLR to remove the subscriber's data.
In this attack, the attacker sends a fraudulent CancelLocation message to the target's current VLR, impersonating the HLR. This tricks the VLR into believing the subscriber has moved to a different location and should be detached from the network.
Once the VLR processes the CancelLocation message, it removes the subscriber's data and terminates any active connections. The subscriber is effectively disconnected from the network and must re-register to restore service.
Attack Flow
- Attacker obtains target's IMSI and current VLR address
- Attacker crafts a CancelLocation message with the target's IMSI
- Attacker spoofs the target's HLR as the source
- Message is sent to the target's current VLR
- VLR processes the request without adequate authentication
- VLR removes the subscriber's data and terminates connections
- Subscriber is disconnected from the network
- Subscriber must re-register to restore service
- Attack can be repeated to cause persistent disruption
Mitigation
Filter CL messages from unauthorized sources
- Filter CL messages from unauthorized sources
- Implement mutual authentication between VLR and HLR
- Verify the source GT against known legitimate HLRs
- Monitor for unusual patterns of CancelLocation messages
- Implement rate limiting for CancelLocation operations
Technical Details
The PurgeMS (Purge Mobile Station) MAP operation is legitimately used by the VLR to inform the HLR that a subscriber's data has been deleted from the VLR, typically due to inactivity or memory constraints.
In this attack, the attacker sends a fraudulent PurgeMS message to the target's HLR, impersonating a VLR. This tricks the HLR into believing the subscriber is no longer registered with any VLR.
As a result, the HLR marks the subscriber as "not reachable" and incoming calls or SMS messages will not be delivered until the subscriber performs a location update by reconnecting to the network.
Attack Flow
- Attacker obtains target's IMSI
- Attacker crafts a PurgeMS message with the target's IMSI
- Attacker spoofs a legitimate VLR as the source
- Message is sent to the target's HLR
- HLR processes the request without adequate authentication
- HLR marks the subscriber as "not reachable"
- Incoming calls and SMS messages are not delivered
- Subscriber remains unreachable until they reconnect
- Attack can be repeated when subscriber reconnects
Mitigation
Validate PurgeMS message sources
- Validate PurgeMS message sources
- Verify that the source VLR previously served the subscriber
- Implement context-aware validation for PurgeMS operations
- Monitor for unusual patterns of PurgeMS messages
- Consider implementing confirmation mechanisms for suspicious requests
Technical Details
The DeleteSubscriberData (DSD) MAP operation is legitimately used by the HLR to remove specific service data from a subscriber's profile in the VLR, typically when services are deactivated or modified.
In this attack, the attacker sends a fraudulent DeleteSubscriberData message to the target's VLR, impersonating the HLR. The message can be crafted to remove essential services or all subscriber data.
When the VLR processes this message, it removes the specified services from the subscriber's profile, potentially rendering the subscription unusable or severely limited in functionality.
Attack Flow
- Attacker obtains target's IMSI and current VLR address
- Attacker crafts a DeleteSubscriberData message with the target's IMSI
- Attacker includes parameters to remove essential services
- Attacker spoofs the target's HLR as the source
- Message is sent to the target's current VLR
- VLR processes the request without adequate authentication
- VLR removes the specified services from the subscriber's profile
- Subscriber experiences service degradation or complete loss
- Full service restoration may require operator intervention
Mitigation
Filter DSD messages based on source
- Filter DSD messages based on source
- Implement mutual authentication between VLR and HLR
- Verify the source GT against known legitimate HLRs
- Monitor for unusual patterns of DeleteSubscriberData messages
- Implement validation for service removal requests
Exploitation Example
from sigploit.ss7.dos import cancelLocation
# Target IMSI (subscriber identity)
target_imsi = '204080123456789'
# Attacker's GT (Global Title)
attacker_gt = '20408999999'
# SS7 connection parameters
ss7_params = {
'sctp_port': 2905,
'target_ip': '10.0.0.1',
'source_pc': 1,
'destination_pc': 2,
'source_ssn': 8,
'destination_ssn': 6
}
# Execute the attack
result = cancelLocation.disrupt(
target_imsi=target_imsi,
attacker_gt=attacker_gt,
**ss7_params
)
print(f"Attack status: {result.get('status')}")
print(f"VLR response: {result.get('response')}")
Ethical Considerations
This code is provided for educational purposes only. Disrupting telecommunications services without authorization is illegal in most jurisdictions and can have serious consequences, especially for emergency communications. Always obtain proper authorization before conducting security testing on telecommunications networks.