free5GC: Missing Concurrent NAS SMC Validation During NGAP Handover

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

free5GC is an open-source implementation of the 5G core network. Prior to 4.2.2, the AMF in Free5GC does not enforce the concurrent security procedure rules defined in 3GPP TS 33.501 §6.9.5.1. The AMF does not check for ongoing N2 handover procedures before initiating a NAS Security Mode Command, and vice versa. This can lead to mismatches between NAS and AS security contexts in the network and the UE. This vulnerability is fixed in 4.2.2.

Source published

27 May 2026 15:59:21 UTC

Source modified

28 May 2026 14:47:44 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 3.1 · 3.7 CVSS:3.1/AV:A/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L

free5GC is an open-source implementation of the 5G core network. Prior to 4.2.2, the AMF in Free5GC does not enforce the concurrent security procedure rules defined in 3GPP TS 33.501 §6.9.5.1. The AMF does not check for ongoing N2 handover procedures before initiating a NAS Security Mode Command, and vice versa. This can lead to mismatches between NAS and AS security contexts in the network and the UE. This vulnerability is fixed in 4.2.2.

Source published

May 27, 2026, 3:59:21 PM (timezone not stated)

Source modified

May 28, 2026, 2:47:44 PM (timezone not stated)

Observed here

9 Nov 2026 10:10:51 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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EUVD CVSS 3.1 · 3.7 CVSS:3.1/AV:A/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L

free5GC is an open-source implementation of the 5G core network. Prior to 4.2.2, the AMF in Free5GC does not enforce the concurrent security procedure rules defined in 3GPP TS 33.501 §6.9.5.1. The AMF does not check for ongoing N2 handover procedures before initiating a NAS Security Mode Command, and vice versa. This can lead to mismatches between NAS and AS security contexts in the network and the UE. This vulnerability is fixed in 4.2.2.

Source published

27 May 2026 17:16:35 UTC

Source modified

14 Oct 2026 20:10:00 UTC

Observed here

25 Oct 2026 10:17:10 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 3.7 CVSS:3.1/AV:A/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L

CVSS 3.1 · [email protected] · Primary · 5.4 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L

### Summary The AMF in Free5GC v4.2.1 does not enforce the concurrent security procedure rules defined in 3GPP TS 33.501 §6.9.5.1. The AMF does not check for ongoing N2 handover procedures before initiating a NAS Security Mode Command, and vice versa. This can lead to mismatches between NAS and AS security contexts in the network and the UE. ### Details **Vulnerability Type:** CWE-358 (Improperly Implemented Security Check for Standard) **Affected File:** `internal/ngap/handler.go` — `handleHandoverRequiredMain()` and `internal/gmm/sm.go` — `SecurityMode()` **Root Cause:** 3GPP TS 33.501 §6.9.5.1 states: > "Concurrent runs of security procedures may, in certain situations, lead to mismatches between security contexts in the network and the UE. In order to avoid such mismatches, the following rules shall be adhered to: > 1. AMF shall not initiate any of the N2 procedures including a new key towards a UE if a NAS Security Mode Command procedure is ongoing with the UE. > 2. The AMF shall not initiate a NAS Security Mode Command towards a UE if one of the N2 procedures including a new key is ongoing with the UE." Free5GC AMF uses an `OnGoing` state tracking mechanism (`SetOnGoing()`, `GetOnGoing()`) with `OnGoingProcedureN2Handover` type. However, the cross-procedure checks required by §6.9.5.1 are not implemented: **Rule 2 violation:** `SecurityMode()` in `internal/gmm/sm.go` sends SMC on `EntryEvent` without checking if N2 handover is ongoing. **Rule 1 violation:** `handleHandoverRequiredMain()` in `internal/ngap/handler.go` calls `SetOnGoing(OnGoingProcedureN2Handover)` without checking if SMC is ongoing. **Why NH/NCC and SMC are related:** SMC activates a new KAMF, which changes the basis for NH key derivation. The N2 HandoverRequest includes NH/NCC derived from the old KAMF. If both procedures run concurrently, the target gNB and UE derive different KgNB keys, breaking AS security. ### PoC **Source code evidence:** Free5GC AMF `internal/gmm/sm.go` — `SecurityMode()`: ```go func SecurityMode(state *fsm.State, event fsm.EventType, args fsm.ArgsType) { switch event { case fsm.EntryEvent: // No check for OnGoing N2 procedure // Directly proceeds to SMC ``` Free5GC AMF `internal/ngap/handler.go` — `handleHandoverRequiredMain()`: ```go amfUe.SetOnGoing(sourceUe.Ran.AnType, &context.OnGoing{ Procedure: context.OnGoingProcedureN2Handover, }) // No check for ongoing SMC before setting N2 ``` **Packet Evidence (pcap available):** | Packet | Time | Message | Description | |--------|------|---------|-------------| | #1 | 0.000s | HandoverRequired | gNB_A requests handover | | #18 | 0.002s | **HandoverRequest** | **N2 started (NH/NCC included)** | | | | *(no response from gNB_B)* | **N2 ongoing** | | #28 | 2.062s | Registration request | UE re-registers (same SUPI) | | #63 | 2.069s | Authentication request | | | #64 | 2.070s | Authentication response | | | #71 | 2.072s | **Security mode command** | **SMC during N2 ongoing = Rule 2 violation** | [NGAPHandover-N2-SMC-Concurrent.zip](https://github.com/user-attachments/files/26735421/NGAPHandover-N2-SMC-Concurrent.zip) ### Impact **Integrity (MEDIUM):** Concurrent NAS and AS security procedures can cause security context mismatches between UE, AMF, and gNB. The SMC activates a new KAMF while the N2 HandoverRequest carries NH/NCC derived from the old KAMF, resulting in KgNB derivation mismatch. **Availability (LOW):** Security context mismatch may cause handover failure or security verification failures.

Source published

7 May 2026 01:56:13 UTC

Source modified

25 Jun 2026 23:11:09 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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CVSS_V3 · CVSS:3.1/AV:A/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L

Publisher rating · LOW

Free5GC AMF has Missing Concurrent NAS SMC Validation During NGAP Handover in github.com/free5gc/amf

Source published

25 Jun 2026 22:34:38 UTC

Source modified

25 Jun 2026 23:01:26 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.