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Merge pull request #1386 from HackTricks-wiki/update_Demystifying_5G_Security__Understanding_the_Regist_20250905_011652
Demystifying 5G Security Understanding the Registration Prot...
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@ -141,17 +141,127 @@ rm -f /tmp/sh ; history -c
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* `Microsocks` + `ProxyChains` : lightweight SOCKS5 pivoting
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* `FRP` (≥0.37) : NAT traversal / asset bridging
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## 9. 5G NAS Registration Attacks: SUCI leaks, downgrade to EEA0/EIA0, and NAS replay
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The 5G registration procedure runs over NAS (Non-Access Stratum) on top of NGAP. Until NAS security is activated by Security Mode Command/Complete, initial messages are unauthenticated and unencrypted. This pre-security window enables multiple attack paths when you can observe or tamper with N2 traffic (e.g., on-path inside the core, rogue gNB, or testbed).
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Registration flow (simplified):
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- Registration Request: UE sends SUCI (encrypted SUPI) and capabilities.
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- Authentication: AMF/AUSF send RAND/AUTN; UE returns RES*.
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- Security Mode Command/Complete: NAS integrity and ciphering are negotiated and activated.
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- PDU Session Establishment: IP/QoS setup.
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Lab setup tips (non-RF):
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- Core: Open5GS default deployment is sufficient to reproduce flows.
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- UE: simulator or test UE; decode using Wireshark.
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- Active tooling: 5GReplay (capture/modify/replay NAS within NGAP), Sni5Gect (sniff/patch/inject NAS on the fly without bringing up a full rogue gNB).
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- Useful display filters in Wireshark:
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- ngap.procedure_code == 15 (InitialUEMessage)
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- nas_5g.message_type == 65 or nas-5gs.message_type == 65 (Registration Request)
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### 9.1 Identifier privacy: SUCI failures exposing SUPI/IMSI
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Expected: UE/USIM must transmit SUCI (SUPI encrypted with the home-network public key). Finding a plaintext SUPI/IMSI in the Registration Request indicates a privacy defect enabling persistent subscriber tracking.
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How to test:
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- Capture the first NAS message in InitialUEMessage and inspect the Mobile Identity IE.
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- Wireshark quick checks:
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- It should decode as SUCI, not IMSI.
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- Filter examples: `nas-5gs.mobile_identity.suci || nas_5g.mobile_identity.suci` should exist; absence plus presence of `imsi` indicates leakage.
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What to collect:
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- MCC/MNC/MSIN if exposed; log per-UE and track across time/locations.
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Mitigation:
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- Enforce SUCI-only UEs/USIMs; alert on any IMSI/SUPI in initial NAS.
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### 9.2 Capability bidding-down to null algorithms (EEA0/EIA0)
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Background:
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- UE advertises supported EEA (encryption) and EIA (integrity) in the UE Security Capability IE of the Registration Request.
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- Common mappings: EEA1/EIA1 = SNOW3G, EEA2/EIA2 = AES, EEA3/EIA3 = ZUC; EEA0/EIA0 are null algorithms.
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Issue:
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- Because the Registration Request is not integrity protected, an on-path attacker can clear capability bits to coerce selection of EEA0/EIA0 later during Security Mode Command. Some stacks wrongly allow null algorithms outside emergency services.
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Offensive steps:
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- Intercept InitialUEMessage and modify the NAS UE Security Capability to advertise only EEA0/EIA0.
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- With Sni5Gect, hook the NAS message and patch the capability bits before forwarding.
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- Observe whether AMF accepts null ciphers/integrity and completes Security Mode with EEA0/EIA0.
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Verification/visibility:
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- In Wireshark, confirm selected algorithms after Security Mode Command/Complete.
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- Example passive sniffer output:
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```
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Encyrption in use [EEA0]
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Integrity in use [EIA0, EIA1, EIA2]
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SUPI (MCC+MNC+MSIN) 9997000000001
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```
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Mitigations (must):
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- Configure AMF/policy to reject EEA0/EIA0 except where strictly mandated (e.g., emergency calls).
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- Prefer enforcing EEA2/EIA2 at minimum; log and alarm on any NAS security context that negotiates null algorithms.
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### 9.3 Replay of initial Registration Request (pre-security NAS)
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Because initial NAS lacks integrity and freshness, captured InitialUEMessage+Registration Request can be replayed to AMF.
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PoC rule for 5GReplay to forward matching replays:
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```xml
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<beginning>
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<property value="THEN"
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property_id="101"
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type_property="FORWARD"
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description="Forward InitialUEMessage with Registration Request">
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<!-- Trigger on NGAP InitialUEMessage (procedureCode == 15) -->
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<event value="COMPUTE"
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event_id="1"
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description="Trigger: InitialUEMessage"
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boolean_expression="ngap.procedure_code == 15"/>
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<!-- Context match on NAS Registration Request (message_type == 65) -->
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<event value="COMPUTE"
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event_id="2"
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description="Context: Registration Request"
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boolean_expression="nas_5g.message_type == 65"/>
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</property>
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</beginning>
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```
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What to observe:
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- Whether AMF accepts the replay and proceeds to Authentication; lack of freshness/context validation indicates exposure.
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Mitigations:
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- Enforce replay protection/context binding at AMF; rate-limit and correlate per-GNB/UE.
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### 9.4 Tooling pointers (reproducible)
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- Open5GS: spin up an AMF/SMF/UPF to emulate core; observe N2 (NGAP) and NAS.
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- Wireshark: verify decodes of NGAP/NAS; apply the filters above to isolate Registration.
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- 5GReplay: capture a registration, then replay specific NGAP + NAS messages as per the rule.
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- Sni5Gect: live sniff/modify/inject NAS control-plane to coerce null algorithms or perturb authentication sequences.
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### 9.5 Defensive checklist
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- Continuously inspect Registration Request for plaintext SUPI/IMSI; block offending devices/USIMs.
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- Reject EEA0/EIA0 except for narrowly defined emergency procedures; require at least EEA2/EIA2.
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- Detect rogue or misconfigured infrastructure: unauthorized gNB/AMF, unexpected N2 peers.
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- Alert on NAS security modes that result in null algorithms or frequent replays of InitialUEMessage.
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---
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## Detection Ideas
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1. **Any device other than an SGSN/GGSN establishing Create PDP Context Requests**.
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2. **Non-standard ports (53, 80, 443) receiving SSH handshakes** from internal IPs.
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3. **Frequent Echo Requests without corresponding Echo Responses** – might indicate GTPDoor beacons.
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4. **High rate of ICMP echo-reply traffic with large, non-zero identifier/sequence fields**.
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5. 5G: **InitialUEMessage carrying NAS Registration Requests repeated from identical endpoints** (replay signal).
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6. 5G: **NAS Security Mode negotiating EEA0/EIA0** outside emergency contexts.
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## References
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- [Palo Alto Unit42 – Infiltration of Global Telecom Networks](https://unit42.paloaltonetworks.com/infiltration-of-global-telecom-networks/)
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- 3GPP TS 29.060 – GPRS Tunnelling Protocol (v16.4.0)
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- 3GPP TS 29.281 – GTPv2-C (v17.6.0)
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- [Demystifying 5G Security: Understanding the Registration Protocol](https://bishopfox.com/blog/demystifying-5g-security-understanding-the-registration-protocol)
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- 3GPP TS 24.501 – Non-Access-Stratum (NAS) protocol for 5GS
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- 3GPP TS 33.501 – Security architecture and procedures for 5G System
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{{#include ../../banners/hacktricks-training.md}}
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