Methods, systems, and computer readable media for mitigating location tracking and denial of service (DoS) attacks that utilize access and mobility management function (AMF) location service

Abstract

A method for mitigating location tracking and DoS attacks that utilize an AMF location service includes receiving, at an NF, an authentication response message from an HPLMN of a UE. The method further includes extracting, by the NF and from the authentication response message, a subscription identifier and an indicator of an authentication result for the UE. The method further includes storing, by the NF and in an AMF location service validation database, the subscription identifier and the indicator of the authentication result for the UE. The method further includes receiving, by the NF, an AMF location service message and using at least one of a subscription identifier extracted from the AMF location service message and contents of the AMF location service validation database, to classify the AMF location service message as a location tracking or DoS attack. The method further includes preventing the location tracking or DoS attack.

Claims

1. A method for mitigating location tracking attacks and denial of service (DoS) attacks that utilize an access and mobility management function (AMF) location service, the method comprising: receiving, at a network function (NF), an authentication response message from a home public land mobile network (HPLMN) of a user equipment (UE), wherein the NF comprises a visited security edge protection proxy (SEPP) of the UE; extracting, by the NF and from the authentication response message, a subscription identifier and an indicator of an authentication result for the UE; storing, by the NF and in an AMF location service validation database, the subscription identifier and the indicator of the authentication result for the UE; receiving, by the NF, an AMF location service message; using, by the NF, at least one of a subscription identifier extracted from the AMF location service message and contents of the AMF location service validation database, to classify the AMF location service message as a location tracking or DoS attack; and in response to classifying the AMF location service message as a location tracking or DoS attack, preventing the location tracking or DoS attack.

2. The method of claim 1 wherein receiving an authentication response message comprises receiving an Nausf_UEAuthentication message containing an authentication result parameter and a subscription permanent identifier (SUPI).

3. The method of claim 2 wherein storing the subscription identifier and the indicator of the authentication result includes storing the SUPI and a value of the authentication result parameter.

4. The method of claim 3 wherein using at least one of the subscription identifier extracted from the AMF location service message and contents of the AMF location service validation database to identify the AMF location service message as a location tracking or DoS attack comprises: extracting a SUPI from the AMF location service message; determining that a source PLMN of the AMF location service message matches a home PLMN of the SUPI extracted from the AMF location service message; performing a lookup in the AMF location service validation database using the SUPI; and classifying the AMF location service message as a DoS attack in response to failing to locate a record corresponding to the SUPI in the AMF location service validation database or locating a record corresponding to the SUPI in the AMF location service validation database and determining that the record includes a value of an authentication result parameter that indicates that authentication of the UE was not successful.

5. The method of claim 1 wherein using at least one of a subscription identifier from the AMF location service message and contents of the AMF location service validation database to classify the AMF location service message as a location tracking or DoS attack includes: extracting a subscription permanent identifier (SUPI) from the AMF location service message; identifying a home PLMN from the SUPI; determining a source PLMN of the AMF location service message; and classifying the AMF location service message as a location tracking attack in response to determining that the home PLMN identified from the SUPI does not match the source PLMN of the AMF location service message.

6. The method of claim 5 wherein determining a source PLMN of the AMF location service message includes determining the source PLMN from a source address or a source transport layer security (TLS) certificate of the AMF location service message.

7. The method of claim 1 wherein receiving an AMF location service message includes receiving an Namf_Location service message.

8. The method of claim 7 wherein the Namf_Location service message includes one of a ProvidePositioningInfo, an EventNotify, and a Provide Location Info service operation identifier.

9. A system for mitigating location tracking and DoS attacks that utilize an access and mobility management function (AMF) location service, the system comprising: a network function (NF) including at least one processor and a memory, wherein the NF comprises a visited security edge protection proxy (SEPP) of the UE; an AMF location service validation database embodied in the memory; an authentication results collector implemented by the at least one processor for receiving an authentication response message from a home public land mobile network (HPLMN) of a user equipment (UE), extracting, from the authentication response message, a subscription identifier and an indicator of an authentication result for the UE, and storing, by the NF and in the AMF location service validation database, the subscription identifier and the indicator of the authentication result for the UE; and an AMF location service validator implemented by the at least one processor for receiving an AMF location service message, using at least one of a subscription identifier extracted from the AMF location service message and contents of the AMF location service validation database to classify the AMF location service message as a location tracking or DoS attack, and, in response to classifying the AMF location service message as a location tracking or DoS attack, preventing the location tracking attack.

10. The system of claim 9 the authentication response message comprises an Nausf_UEAuthentication message containing an authentication result parameter and a subscription permanent identifier (SUPI).

11. The system of claim 10 wherein storing the subscription identifier comprises the SUPI and the indicator of the authentication result includes a value of the authentication result parameter.

12. The system of claim 11 wherein, in using at least one of the subscription identifier extracted from the AMF location service message and contents of the AMF location service validation database to identify the AMF location service message as a location tracking or DoS attack, the AMF location service validator is configured to: extract a SUPI from the AMF location service message; determine that a source PLMN of the AMF location service message matches a home PLMN of the SUPI extracted from the AMF location service message; perform a lookup in the AMF location service validation database using the SUPI; and classify the AMF location service message as a DoS attack in response to failing to locate a record corresponding to the SUPI in the AMF location service validation database or locating a record corresponding to the SUPI in the AMF location service validation database and determining that the record includes a value of an authentication result parameter that indicates that authentication of the UE was not successful.

13. The system of claim 9 wherein, in using at least one of a subscription identifier from the AMF location service message and contents of the AMF location service validation database to classify the AMF location service message as a location tracking or DoS attack, the AMF location service validator is configured to: extract a subscription permanent identifier (SUPI) from the AMF location service message; identify a home PLMN from the SUPI extracted from the AMF location service message; determine a source PLMN of the AMF location service message; and classify the AMF location service message as a location tracking attack in response to determining that the home PLMN identified from the SUPI does not match the source PLMN of the AMF location service message.

14. The system of claim 13 wherein the AMF location service validator is configured to determine a source PLMN of the AMF location service message by determining the source PLMN from a source address or a source transport layer security (TLS) certificate of the AMF location service message.

15. The system of claim 9 wherein the AMF location service message comprises an Namf_Location service message including one of a ProvidePositioningInfo, an EventNotify, and a ProvideLocationInfo service operation identifier.

16. A non-transitory computer readable medium having stored thereon executable instructions that when executed by a processor of a computer control the computer to perform steps comprising: receiving, at a network function (NF), an authentication response message from a home public land mobile network (HPLMN) of a user equipment (UE), wherein the NF comprises a visited security edge protection proxy (SEPP) of the UE; extracting, by the NF and from the authentication response message, a subscription identifier and an indicator of an authentication result for the UE; storing, by the NF and in an access and mobility management function (AMF) location service validation database, the subscription identifier and the indicator of the authentication result for the UE; receiving, by the NF, an AMF location service message; using, by the NF, at least one of a subscription identifier extracted from the AMF location service message and contents of the AMF location service validation database, to classify the AMF location service message as a location tracking or denial of service (DoS) attack; and in response to classifying the AMF location service message as a location tracking or DoS attack, preventing the location tracking or DoS attack.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a network diagram illustrating an exemplary 5G system network architecture;

(2) FIG. 2 is a message flow diagram illustrating exemplary messages exchanged for the Provide Positioning Info service operation of the Namf_Location service;

(3) FIG. 3 is a diagram illustration exemplary UE geographic location information that can obtained using the ProvidePositioningInfo and the ProvideLocationInfo service operations of the Namf_Location service;

(4) FIG. 4 is a message flow diagram illustrating exemplary messages exchanged for a legitimate access to the Namf_Location service and for a location tracking attack;

(5) FIG. 5 is a message flow diagram illustrating exemplary messages exchanged and steps performed by a visited SEPP in obtaining and storing UE subscription identification information and authentication result information from the Nausf authentication procedure;

(6) FIG. 6 is a message flow diagram illustrating the use of stored UE subscription identification and authentication result information to validate AMF location service request messages and to prevent location tracking attacks and DoS attacks that utilize an AMF location service;

(7) FIG. 7 is a block diagram illustrating an exemplary architecture for an SEPP capable of validating AMF location service messages using the methodology described herein; and

(8) FIG. 8 is a flow chart illustrating an exemplary process for mitigating location tracking attacks and DoS attacks that utilize an AMF location service.

DETAILED DESCRIPTION

(9) FIG. 1 is a block diagram illustrating an exemplary 5G system network architecture. The architecture in FIG. 1 includes NRF 100 and SCP 101, which may be located in the same home public land mobile network (HPLMN). As described above, NRF 100 may maintain profiles of available producer NF service instances and their supported services and allow consumer NFs or SCPs to subscribe to and be notified of the registration of new/updated producer NF service instances. SCP 101 may also support service discovery and selection of producer NF instances. SCP 101 may perform load balancing of connections between consumer and producer NFs.

(10) NRF 100 is a repository for NF or service profiles of producer NF instances. In order to communicate with a producer NF instance, a consumer NF or an SCP must obtain the NF or service profile of the producer NF instance from NRF 100. The NF or service profile is a JavaScript object notation (JSON) data structure defined in Third Generation Partnership Project (3GPP) Technical Specification (TS) 29.510. The NF or service profile definition includes at least one of a fully qualified domain name (FQDN), an Internet protocol (IP) version 4 (IPv4) address or an IP version 6 (IPv6) address.

(11) In FIG. 1, any of the network functions can be consumer NFs producer NFs, or both, depending on whether they are requesting, providing, or requesting and providing services. In the illustrated example, the NFs include a PCF 102 that performs policy related operations in a network, a UDM function 104 that manages user data, and an application function (AF) 106 that provides application services.

(12) The NFs illustrated in FIG. 1 further include a session management function (SMF) 108 that manages sessions between access and mobility management function (AMF) 110 and PCF 102. AMF 110 performs mobility management operations similar to those performed by a mobility management entity (MME) in 4G networks. An authentication server function (AUSF) 112 performs authentication services for user equipment (UEs), such as user equipment (UE) 114, seeking access to the network.

(13) A network slice selection function (NSSF) 116 provides network slicing services for devices seeking to access specific network capabilities and characteristics associated with a network slice. A network exposure function (NEF) 118 provides application programming interfaces (APIs) for application functions seeking to obtain information about Internet of things (IoT) devices and other UEs attached to the network. NEF 118 performs similar functions to the service capability exposure function (SCEF) in 4G networks.

(14) A radio access network (RAN) 120 connects user equipment (UE) 114 to the network via a wireless link. Radio access network 120 may be accessed using a g-Node B (gNB) (not shown in FIG. 1) or other wireless access point. A user plane function (UPF) 122 can support various proxy functionality for user plane services. One example of such proxy functionality is multipath transmission control protocol (MPTCP) proxy functionality. UPF 122 may also support performance measurement functionality, which may be used by UE 114 to obtain network performance measurements. Also illustrated in FIG. 1 is a data network (DN) 124 through which UEs access data network services, such as Internet services.

(15) SEPP 126 filters incoming traffic from another PLMN and performs topology hiding for traffic exiting the home PLMN. SEPP 126 may communicate with an SEPP in a foreign PLMN which manages security for the foreign PLMN. Thus, traffic between NFs in different PLMNs may traverse two SEPP functions, one for the home PLMN and the other for the foreign PLMN.

(16) As described above, one problem with the 3GPP network architecture for 5G networks is that the Namf_Location service defined in 3GPP TS 29.518 does not require resource object level authorization before providing location information for a UE. Table 1 shown below illustrates the various types of messages that can be used in the in Namf_Location service to obtain location information regarding a UE or to institute a denial of service attack on an AMF.

(17) TABLE-US-00001 TABLE 1 Namf_Location Service Operations Operation Known Service Name Service Operation Semantic Consumer(s) Namf_Location ProvidePositioningInfo Request/Response GMLC EventNotify Subscribe/Notify GMLC ProvideLocationInfo Request/Response UDM CancelLocation Request/Response GMLC
In Table 1, the Namf_Location service includes the ProvidePositioningInfo service operation, the EventNotify service operation, the ProvideLocationInfo service operation, and the CancelLocation service operation. The ProvidePositioningInfo info service operation is used by an NF service consumer, such as a gateway mobile location center (GMLC) to request the current or deferred geodetic an optionally civic location of a UE. This operation triggers the AMF to invoke service towards the location management function (LMF). The EventNotify service operation notifies the NF service consumer about UE location-related event information related to security sessions or deferred location, i.e., the initiation, handover, or termination of an emergency session or the completion or activation of deferred location. The ProvideLocationInfo service operation allows an NF service consumer, such as a UDM, to request the network provided location information (NPLI) of a target UE. The CancelLocation service operation is invoked by an NF service consumer, such as a GMLC, to cancel reporting periodic or event-triggered location.

(18) All of the services operations illustrated in Table 1 are triggered by either sending a request or a subscribe message to the AMF currently serving a UE. FIG. 2 illustrates an example of messages that are exchanged in the ProvidePositioningInfo service. Referring to FIG. 2, and NF service consumer 200 invokes the Provide Positioning Info service in line 1 by sending an HTTP Post message to AMF 110. The HTTP Post message includes the ProvidePositioningInfo URI, which identifies the ProvidePositioningInfo service operation. The HTTP Post message also includes an individual UE context. The individual UE context includes a UE context ID, which identifies the UE. In one example, the individual UE context may be composed or made of the UE's subscription permanent identifier (SUPI), which is a global identifier for the UE in the network.

(19) In response to the post message containing the ProvidePositioningInfo service operation, AMF 110 may respond as indicated in step 2A where AMF 110 provides the requested UE positioning info, in step 2B where AMF 110 indicates no content is present for the UE, or as in step 2C, where AMF 110 indicates that there were problems in invoking the requested service operation.

(20) It should be noted that there is no authentication of NF service consumer 200 as part of the Namf ProvidePositioningInfo service operation. Similar messages may be exchanged for the other Namf_Location service operations listed above in Table 1, none of which has a defined authentication mechanism.

(21) FIG. 3 illustrates an example of output from the ProvidePositioningInfo and ProvideLocationInfo service operations. As illustrated in FIG. 3, both service operations can output geographic position or coordinates of the UE. Both service operations can also output an age of location, which indicates the age or time that a particular UE location was reported. The output of the ProvidePositioningInfo service operation also includes a velocity estimate, which may suggest how fast a UE is moving. Because output of both of these service operations can be used to pinpoint the location of the UE and the time that a UE is at that particular location, it is desirable to prevent unauthorized access to this information. It is also desirable to prevent any of the message in Table 1 from being used to implement a DoS attack against an AMF.

(22) FIG. 4 is a message flow diagram illustrating exemplary messages exchanged for a legitimate access to the Namf_Location service and for a location tracking or DoS attack. Referring to FIG. 4, consumer NF 200 and home SEPP 126A are components of the home network of a UE. Visited SEPP 126B and AMF 110 are components of the visited network in which the UE is currently roaming. An attacker 400 is located outside of both the home and visited networks. However, the subject matter described herein also is capable of detecting location tracking attacks from within the home and visited networks of a UE.

(23) In line 1 of the message flow illustrated in FIG. 4, consumer NF 200 sends an Namf_Location request message to H-SEPP 126A. In line 2, H-SEPP 126A forwards the Namf_Location service request to V-SE PP 126B located in the visited network. In line 3, V-SEPP 126B forwards the Namf_Location service request to AMF 110.

(24) In line 4, AMF 110 sends an Namf_Location service response to V-SEPP 126B. The Namf_Location service response contains the requested location information of the UE. In line 5, V-SEPP 126B sends the Namf_Location service response to H-SEPP 126A. In line 6, H-SEPP 126A forwards the location service response to consumer NF 200, which is the node that requested the data.

(25) Lines 1-6 illustrate the legitimate use of the Namf_Location service by consumer NF 200 located in the home network of the UE. However, in line 7, a consumer NF 400 controlled by an attacker and masquerading as a legitimate service user sends an Namf_Location service request message to V-SEPP 126B. In line 8, V-SEPP 126B forwards the Namf_Location service request to AMF 110. AMF 110 does not perform any authentication of the request and, in line 9, responds with the requested UE location data in an Namf_Location service response message.

(26) In line 10, V-SEPP 126B forwards the Namf_Location service response to consumer NF 400. Because consumer NF 400 has access to location information regarding the subscriber, consumer NF 400 can report this location to a criminal, who can use the location information for nefarious purposes. In addition, consumer NF can initiate multiple unauthorized Namf_Location service request messages to AMF 110 to overwhelm the resources of AMF 110 in a DoS attack.

(27) In order to mitigate or guard against location tracking attacks, such as that illustrated in FIG. 4, and DoS attacks that utilize the Namf location service, a network function, such as an SEPP, may store subscription identification information and authentication obtained from the UE authentication request from an AUSF and use the subscription identification and authentication result information to validate AMF location service messages concerning the UE.

(28) FIG. 5 is a message flow diagram illustrating exemplary messages exchanged and steps performed by a visited SEPP in obtaining and storing UE subscription identification information and authentication result information from the Nausf authentication procedure. Referring to FIG. 5, when a UE registers with an AMF, the AMF sends an Nausf_UEAuthentication_Authenticate request message to the home network of the UE, as indicated by line 1 of the message flow diagram. The Nausf_UEAuthentication_Authenticate request message includes the subscription concealed identifier (SUCI) and an identifier for the serving network in which the UE is currently located. In line 2 of the message flow diagram, V-SEPP 126B forwards the in a Nausf_UEAuthentication_Authenticate request message to H-SEPP 126A. In line 3 of the message flow diagram, H-SEPP 126A forwards the Nausf_UEAuthentication message to AUSF 112.

(29) In line 4 of the message flow diagram, AUSF 112 receives the Nausf_UEAuthentication_Authenticate request, determines whether the requesting AMF in the serving network is entitled to use the serving network name in the Nausf_UEAuthentication_Authenticate request, and sends an Nudm_UEAuthentication_Get request message to UDM 104. The Nudm_UEAuthentication_Get request message contains the SUCI and the serving network name.

(30) Upon receiving the Nudm_UEAuthentication_Get request, UDM 104 de-conceals the SUCI to determine the SUPI. Based on the SUPI, UDM 104 selects an authentication method. In line 5 of the message flow diagram, UDM 104 sends an Nudm_UEAuthentication_Get response message to AUSF 112. The Nudm_UEAuthentication_Get response message contains an authentication vector (AV) containing authentication challenge information according to the selected authentication method. The Nudm_UEAuthentication_Get response message also includes the SUPI. In line 6 of the message flow diagram, AUSF 112 generates and sends an Nausf_UEAuthentication_Authenticate response message containing the authentication vector and an authentication context ID to H-SEPP 126A. In line 7 of the message flow diagram, H-SEPP 126A forwards the Nausf_UEAuthentication_Authenticate response to V-SEPP 126B. In line 8, V-SEPP 126B forwards the Nausf_UEAuthentication_Authenticate response to AMF 110.

(31) AMF 110 receives the Nausf_UEAuthentication_Authenticate response message including the authentication vector and sends an authentication request message to the UE with the authentication vector including the authentication challenge information. The UE calculates an authentication response based on the authentication challenge information. In one type of authentication, the authentication response is a Res* value computed by the UE using a secure hash algorithm. The UE communicates the Res* value to AMF 110 in an authentication response message. In line 9, AMF 110 forwards the Res* value to V-SEPP 126B in an Nausf_UEAuthentication_Authenticate request message. In line 10, V-SEPP 126B forwards the Nausf_UEAuthentication_Authenticate request message to H-SEPP 126A. In line 11, H-SEPP 126A forwards the Nausf_UEAuthentication_Authenticate request to AUSF 112. In line 12, AUSF 112 formulates and sends an Nudm_UEAuthentication request message UDM 104. In line 13, UDM 104 authenticates the UE based on the Res* value and responds to the Nudm_UEAuthentication request message by sending an Nudm_UEAuthentication response message containing an authentication result parameter and the SUPI of the UE. The value of the authentication result parameter indicates whether the authentication of the UE was successful or not. In line 14, AUSF 112 responds to the Nudm_UEAuthentication response by generating and sending an Nausf_UEAuthentication response including the authentication result and the SUPI to H-SEPP 126A. In line 15, H-SEPP 126A forwards the Nausf_UEAuthentication response to V-SEPP 126B.

(32) Rather than simply forwarding the Nausf_UEAuthentication response message to AMF 110, V-SEPP 126B extracts the value of the authentication result parameter and the SUPI from the Nausf_UEAuthentication response and stores the SUPI and the value of the authentication result parameter in an AMF location service validation database. In line 17, V-SEPP 126B forwards the Nausf_UEAuthentication response message to AMF 110.

(33) Once V-SEPP 126B stores the SUPI and the authentication result, this data can be used to validate future AMF location service request and subscribe messages. FIG. 6 is a message flow diagram illustrating the use of stored UE subscription identification and authentication result information to validate AMF location service messages and to prevent a location tracking attack or a DoS attack that utilizes AMF location service messages. Referring to FIG. 6, in line 1, a consumer NF 200 located in the home PLMN sends an AMF location service request message to H-SEPP 126A. In line 2, H-SEPP 126A forwards the AMF location service request to V-SEPP 126B. Rather than simply forwarding the AMF location service request message to AMF 110, in step 3, V-SEPP 126B checks the source PLMN in the AMF location service request against the SUPI and checks the authentication result stored for the SUPI to determine whether the UE was authenticated. Table 2 shown below Illustrates an example of the UE content text identification information that may be included in the AMF location service request message.

(34) TABLE-US-00002 TABLE 2 UE Context ID Information Contained in Location Service Request Data Name type Definition apiRoot string See clause 6.4.1 apiVersion string See clause 6.4.1. ueContextId string Represents the Subscription Permanent Identifier (see 3GPP TS 23.501 [2] clause 5.9.2) pattern: see pattern of type Supi in 3GPP TS 29.571 [6] Or represents the Permanent Equipment Identifier (see 3GPP TS 23.501 [2] clause 5.9.3) pattern: “(imei-[0-9]{15}|imeisv-[0-9]{16}|.+)”
Table 2 is a copy of Table 6.4.3.2.2-1 of 3GPP TS 29.518, which specifies the resource URI variables for the UE context ID that is carried in the location service request message. As indicated in Table 2, the UE context ID includes either the SUPI or a permanent equipment identifier. The pattern for the SUPI is defined in 3GPP TS 23.501. In this example, it is assumed that the SUPI is present in the AMF location service request message. Clause 5.9.2 of 3GPP TS 23.501 states the following regarding the SUPI:
A globally unique 5G Subscription Permanent Identifier (SUPI) shall be allocated to each subscriber in the 5G System and provisioned in the UDM/UDR. The SUPI is used only inside 3GPP system, and its privacy is specified in TS 33.501 [29]. The SUPI may contain: an IMSI as defined in TS 23.003 [19], or a network-specific identifier, used for private networks as defined in TS 22.261 [2]. a GLI and an operator identifier of the 5GC operator, used for supporting FN-BRGs, as further described in TS 23.316 [84]. a GCI and an operator identifier of the 5GC operator, used for supporting FN-CRGs and 5G-CRG, as further described in TS 23.316 [84].
A SUPI containing a network-specific identifier shall take the form of a Network Access Identifier (NAI) using the NAI RFC 7542 [20] based user identification as defined in TS 23.003 [19].
When UE needs to indicate its SUPI to the network (e.g. as part of the Registration procedure), the UE provides the SUPI in concealed form as defined in TS 23.003 [19].
In order to enable roaming scenarios, the SUPI shall contain the address of the home network (e.g. the MCC and MNC in the case of an IMSI based SUPI).
For interworking with the EPC, the SUPI allocated to the 3GPP UE shall always be based on an IMSI to enable the UE to present an IMSI to the EPC.
As indicated above in the passages from 3GPP TS 23.501, the SUPI may contain a globally unique identifier for the UE and may also contain the address of the home network or HPLMN. Thus, the validation of the AMF location service request message in step 3 of FIG. 6 may be performed as follows: 1. Extract the SUPI from the AMF location service message. 2. Determine whether the source PLMN of the AMF location service message matches the home PLMN specified in the SUPI of the AMF location service message. As indicated in the excerpt above from 3GPP TS 23.501, the SUPI contains the address of the home network, which can be in the form of a mobile network code (MNC) and a mobile country code (MCC). These parameters can be compared with the MNC and MCC of the source PLMN of the AMF location service message. The source PLMN of the AMF location service message can be identified from a source TLS certificate or a source address of the message (e.g., source IP address or source domain). The AMF location service validation database may include a table that maps source IP addresses or domains to MNCs and MCCs of known networks. Thus, the source address extracted from the message may be used to identify the MNC and MCC of the source network, and these parameters may be compared with the MNC and MCC extracted from the SUPI. If the source PLMN from the TLS certificate is used, the source PLMN from the TLS certificate obtained from the AMF location service message may be compared with the MNC, MCC, or other home-network-identifying parameter contained in or derived from the SUPI. 3. If the source PLMN in the AMF location service message does not match the home PLMN in the SUPI of the AMF location service message, validation fails. 4. If the source PLMN in the AMF location service message matches the home PLMN in the SUPI of the AMF location service message, perform a lookup for the SUPI in the AMF location service validation database. 5. If the SUPI from the AMF location service message is not present in the AMF location service validation database, validation fails. 6. If the SUPI from the AMF location service message is present in the AMF location service validation database, check the authentication result in the matching database record. 7. If the authentication result in the database record indicates that the UE was not authenticated, validation fails. 8. If the authentication result in the database record indicates that the UE was authenticated, validation passes.

(35) Table 3 shown below illustrates an exemplary record that may be present in the AMF location service validation database after the storage of the authentication result and SUPI information obtained from the Nausf authentication procedure illustrated in FIG. 5.

(36) TABLE-US-00003 TABLE 3 Example AMF Location Service Validation Database Record SUPI AUTHENTICATION RESULT SUPI1 AUTHENTICATED
In Table 3, the database record includes SUPI1, which was obtained from the UDM in the HPLMN of the subscriber using the procedure of FIG. 5. The authentication result of AUTHENTICATED indicates that the authentication of the UE was successful.

(37) Continuing with the message flow in FIG. 6, in the example in step 3, the AMF location service request is validated using the steps described above. Accordingly, in line 4, V-SEPP 126B forwards the AMF location service request to AMF 110. In line 5, AMF 110 generates and sends an AMF location service response message including the requested UE location information to V-SEPP 126B. In line 6, V-SEPP 126B forwards the AMF location service response to H-SEPP 126A. In line 7, H-SEPP 126A forwards the AMF location service response to consumer NF 200.

(38) In line 8 of the message flow illustrated in FIG. 6, consumer NF 400, which in this example is a hacker or an attacker, sends an AMF location service request to V-SEPP 126B, which is the SEPP for the visited network where the UE is currently roaming. V-SEPP 126B classifies the AMF location service request as being a location tracking or DoS attack using the steps described above. To reiterate, the AMF location service request may be classified as a location tracking attack if the source PLMN of the message does not match the home PLMN in the SUPI, the SUPI is not present in the AMF location service validation database, or as a DoS attack if the SUPI is present in the AMF location service validation database and the authentication result stored for the SUPI indicates that the UE has not been successfully authenticated. In this case, V-SEPP 126B prevents the AMF location service request from being forwarded to AMF 110 and may discard the location service request and optionally generate a record of the location service request for delivery to the network operator. Thus, using the steps in FIG. 6, a SUPI and authentication result stored during an Namf authentication procedure triggered by registration of a UE at an AMF is used to validate an AMF location service request (in step 3) and to reject an AMF location service request from an attacker (in line 8).

(39) FIG. 7 is a block diagram illustrating an exemplary architecture for an SEPP capable of validating AMF location service request messages using the methodology described herein. Referring to FIG. 7, an SEPP that implements the subject matter described herein may be a visited SEPP of the UE whose location or positioning information is being protected. In the examples described above, AMF location service validation is performed by V-SEPP 126B for a roaming subscriber that is registered with an AMF in a VPLMN.

(40) In the example architecture illustrated in FIG. 7, SEPP 126B includes at least one processor 700 and a memory 702. SEPP 126B includes an AMF location service validation database 704 that stores SUPIs and authentication result information obtained from the Nausf authentication procedure described above. Home or visited SEPP 126B further includes a UE authentication results collector 706 for performing the steps described above with regard to FIG. 5 for obtaining UE authentication information and SUPI information and storing the information in database 704. SEPP 126A further includes an AMF location service validator 708 for validating or rejecting AMF location service messages using the SUPI and authentication result information stored in database 704. In one exemplary implementation, UE authentication results collector 706 and AMF location service validator 708 may be implemented using computer executable instructions embodied in memory 702 and executable by processor 700.

(41) FIG. 8 is a flow chart illustrating an exemplary process for mitigating location tracking and DoS attacks. Referring to FIG. 8, in step 800, the process includes receiving, at a network function, an authentication response message from a home public land mobile network of a UE. For example, an SEPP, such as visited SEPP 126B may receive an Nausf_UEAuthentication response message, as indicated by line 14 in FIG. 5.

(42) In step 802, the process includes extracting, by the NF and from the authentication response message, a subscription identifier and an indicator of an authentication result for the UE. For example, visited SEPP 126B may extract the SUPI and the value of an authentication result parameter from the Nausf_UEAuthentication response message.

(43) In step 804, the process includes storing, by the NF and in an AMF location service validation database, the subscription identifier and the authentication result. For example, visited SEPP 126B may store the SUPI and the value of the authentication result parameter extracted from the Nausf_UEAuthentication response message in the AMF location service validation database.

(44) In step 806, the process includes receiving, by the NF, an AMF location service message. For example, visited SEPP 126B may receive an AMF location service message, where the AMF location service message is any of the message types illustrated in Table 1 that request or subscribe to receive location or position information regarding a UE. Examples of such messages may include messages carrying the ProvidePositioningInfo service operation identifier, the ProvideLocationInfo service operation identifier, or the EventNotify service operation identifier.

(45) In step 808, the process includes using at least one of: the subscription identifier from the AMF location service message and contents of the AMF location service validation database to classify the AMF location service message as a location tracking or DoS attack. For example, visited SEPP 126B may determine that the source PLMN of the message does not match the home PLMN in the SUPI extracted from the message to identify the message as a location tracking attack. If the source PLMN of the message matches the home PLMN included in the SUPI, the SEPP may perform a lookup in the AMF location service validation database using the SUPI extracted from the AMF location service message. If the SUPI is not present in the database or if the authentication result obtained from the database does not indicate that the UE was authenticated, the AMF location service message may be classified as a DoS attack.

(46) In step 810, the process includes, in response to classifying the AMF location service message as a location tracking or DoS attack, preventing the location tracking or DoS attack. For example, visited SEPP 126B, in response to classifying the AMF location service message as being a location tracking or DoS attack, may prevent the attack by discarding the message. Visited SEPP 126B may also store the message and send a message to the network operator identifying the message as being associated with a location tracking attack or DoS.

(47) Advantages of the subject matter described herein include mitigating or reducing successful location tracking attacks where the location of a UE can be obtained without authorization. The subject matter described herein also mitigates or reduces successful denial of service attacks at the AMF because unauthorized AMF location service messages identified as being associated with a location tracking or DoS attack will be stopped at the SEPP and prevented from being forwarded to the AMF. The subject matter described herein can be implemented at any NF that processes or forwards AMF location service messages, including a visited SEPP of the UE and the AMF at which the UE is registered. The subject matter described herein may also be extended to validate other types of inter-PLMN messaging towards the visited SEPP.

(48) The disclosure of each of the following references is hereby incorporated herein by reference in its entirety.

REFERENCES

(49) 1. 3GPP TS 33.501 V17.0.0 (2020 December) 3.sup.rd Generation Partnership Project; Technical Specification Group Services and System Aspects; Security Architectures and Procedures for 5G System (Release 17). 2. 3GPP TS 29.573 V16.5.0 (2020 December) 3.sup.rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; 5G System; Public Land Mobile Network (PLMN) Interconnection; Stage 3 (Release 16). 3. 3GPP TS 29.572 V16.5.0 (2020 December) 3.sup.rd Generation Partnership Project Technical Specification Group Core Network and Terminals; 5G System; Location Management Services; Stage 3 (Release 16). 4. 3GPP TS 29.518 V17.0.0 (2020 December) 3.sup.rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; 5G System; Access and Mobility Management Services; Stage 3 (Release 17). 5. 3GPP TS 23.502 V16.7.1 (2021 January), 3.sup.rd Generation Partnership Project; Technical Specification Group Services and System Aspects; Procedures for the 5G System (5GS); Stage 2 (Release 16). 6. 3GPP TS 23.501 V16.7.0 (2020 December), 3.sup.rd Generation Partnership Project; Technical Specification Group Services and System Aspects; System Architecture for the 5G System (5GS), Stage 2 (Release 16).

(50) It will be understood that various details of the subject matter described herein may be changed without departing from the scope of the subject matter described herein. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation, as the subject matter described herein is defined by the claims as set forth hereinafter.