free5GC: UE Security Capability bypass on NGAP PathSwitchRequest

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 verify the UE Security Capabilities received in NGAP PathSwitchRequest messages against its locally stored values, as mandated by 3GPP TS 33.501 §6.7.3.1. A malicious gNB can overwrite the AMF's stored UE security capabilities with arbitrary values, which are then propagated in PathSwitchRequest Acknowledge messages and subsequent Handover Request messages. This leads to persistent handover denial-of-service for affected UEs. This vulnerability is fixed in 4.2.2.

Source published

27 May 2026 15:59:58 UTC

Source modified

27 May 2026 17:56:05 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · 6.1 CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/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 verify the UE Security Capabilities received in NGAP PathSwitchRequest messages against its locally stored values, as mandated by 3GPP TS 33.501 §6.7.3.1. A malicious gNB can overwrite the AMF's stored UE security capabilities with arbitrary values, which are then propagated in PathSwitchRequest Acknowledge messages and subsequent Handover Request messages. This leads to persistent handover denial-of-service for affected UEs. This vulnerability is fixed in 4.2.2.

Source published

May 27, 2026, 3:59:58 PM (timezone not stated)

Source modified

May 27, 2026, 5:56:05 PM (timezone not stated)

Observed here

9 Nov 2026 10:10:50 UTC

Source terms

ENISA EUVD · source terms and attribution apply

Original source record · Cite this exact observation · Complete original publisher JSON

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

EUVD CVSS 3.1 · 6.1 CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/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 verify the UE Security Capabilities received in NGAP PathSwitchRequest messages against its locally stored values, as mandated by 3GPP TS 33.501 §6.7.3.1. A malicious gNB can overwrite the AMF's stored UE security capabilities with arbitrary values, which are then propagated in PathSwitchRequest Acknowledge messages and subsequent Handover Request messages. This leads to persistent handover denial-of-service for affected UEs. This vulnerability is fixed in 4.2.2.

Source published

27 May 2026 17:16:34 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

Original source record · Cite this exact observation · Complete original publisher JSON

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 · 6.1 CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:L

CVSS 3.1 · [email protected] · Primary · 7.1 CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H

### Summary The AMF in Free5GC v4.2.1 does not verify the UE Security Capabilities received in NGAP PathSwitchRequest messages against its locally stored values, as mandated by 3GPP TS 33.501 §6.7.3.1. A malicious gNB can overwrite the AMF's stored UE security capabilities with arbitrary values, which are then propagated in PathSwitchRequest Acknowledge messages and subsequent Handover Request messages. This leads to persistent handover denial-of-service for affected UEs. ### Details **Affected File:** `amf/internal/ngap/handler.go` — `handlePathSwitchRequestMain` function **Root Cause:** When the AMF receives a PathSwitchRequest during an Xn-handover, it processes the UESecurityCapabilities IE by directly overwriting the stored values without comparing them to the previously stored capabilities: ```go if uESecurityCapabilities != nil { amfUe.UESecurityCapability.SetEA1_128_5G(uESecurityCapabilities.NRencryptionAlgorithms.Value.Bytes[0] & 0x80) amfUe.UESecurityCapability.SetEA2_128_5G(uESecurityCapabilities.NRencryptionAlgorithms.Value.Bytes[0] & 0x40) amfUe.UESecurityCapability.SetEA3_128_5G(uESecurityCapabilities.NRencryptionAlgorithms.Value.Bytes[0] & 0x20) amfUe.UESecurityCapability.SetIA1_128_5G(uESecurityCapabilities.NRintegrityProtectionAlgorithms.Value.Bytes[0] & 0x80) amfUe.UESecurityCapability.SetIA2_128_5G(uESecurityCapabilities.NRintegrityProtectionAlgorithms.Value.Bytes[0] & 0x40) amfUe.UESecurityCapability.SetIA3_128_5G(uESecurityCapabilities.NRintegrityProtectionAlgorithms.Value.Bytes[0] & 0x20) } ``` **3GPP TS 33.501 §6.7.3.1 requires three actions, none of which are implemented:** 1. **Verification (SHALL):** "The AMF shall verify that the UE's 5G security capabilities received from the target gNB/ng-eNB are the same as the UE's 5G security capabilities that the AMF has locally stored." → Not implemented. The AMF unconditionally overwrites stored values. 2. **Correction (SHALL):** "If there is a mismatch, the AMF shall send its locally stored 5G security capabilities of the UE to the target gNB/ng-eNB in the Path-Switch Acknowledge message." → Not implemented. The PathSwitchRequestAcknowledge contains the corrupted values. 3. **Logging (SHALL):** "The AMF shall support logging capabilities for this event and may take additional measures, such as raising an alarm." → Not implemented. No mismatch detection or logging exists. **Propagation:** The corrupted values are propagated in: - **PathSwitchRequestAcknowledge:** Contains corrupted UESecurityCapabilities (demonstrated in pcap) - **Subsequent HandoverRequest messages:** AMF sends corrupted capabilities to target gNBs Per TS 38.413 §8.4.2.4, if the supported algorithms in the UE Security Capabilities do not match any allowed algorithms configured in the target gNB, the target gNB is required to reject the procedure using a HANDOVER FAILURE message. ### PoC **Environment:** - Free5GC v4.2.1 AMF (Docker container) with full NF stack (NRF, AUSF, UDM, UDR, NSSF, PCF, SMF, UPF) - UERANSIM v3.2.7 gNB with custom inspection-tool extension - tshark for packet capture **Reproduction Steps:** 1. Start Free5GC full stack and register a UE through a gNB (NG Setup → Registration → PDU Session Setup). 2. Send a normal HandoverRequired from the gNB. Capture the resulting HandoverRequest from the AMF and confirm `nRintegrityProtectionAlgorithms = 0xe000` (NIA1, NIA2, NIA3 all supported). This is the baseline. 3. Send a PathSwitchRequest with `nRintegrityProtectionAlgorithms = 0x0000` (all integrity algorithms set to not supported). The AMF responds with PathSwitchRequestAcknowledge. 4. Observe that the PathSwitchRequestAcknowledge contains `nRintegrityProtectionAlgorithms = 0x0000` — the corrupted values are propagated back. **Observed Result (from pcap capture):** | Packet | Message | nRintegrityProtectionAlgorithms | |--------|---------|-------------------------------| | #20 | HandoverRequest (AMF→gNB) | `0xe000` (NIA1 ✓ NIA2 ✓ NIA3 ✓) — **baseline** | | #30 | PathSwitchRequest (gNB→AMF) | `0x0000` — **poison** | | #47 | PathSwitchRequestAcknowledge (AMF→gNB) | `0x0000` (NIA1 ✗ NIA2 ✗ NIA3 ✗) — **corrupted** | ### Impact **Availability (HIGH):** A malicious gNB can send a single PathSwitchRequest message to corrupt the AMF's stored UE security capabilities for any UE. All subsequent inter-gNB handovers for the affected UE are expected to fail (per TS 38.413 §8.4.2.4), resulting in denial-of-service that persists until the UE performs a new registration. **Integrity (LOW):** The AMF's internal UE security context is corrupted with attacker-controlled values. These corrupted values are propagated to other network elements via PathSwitchRequestAcknowledge and HandoverRequest messages. **Who is impacted:** Any deployment using Free5GC as the AMF where a gNB could be compromised or where untrusted gNBs exist (e.g., O-RAN multi-vendor deployments).

Source published

7 May 2026 01:53:47 UTC

Source modified

25 Jun 2026 19:56:07 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

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

Publisher rating · MODERATE

Free5GC AMF Bypasses UE Security Capabilities on NGAP PathSwitchRequest in github.com/free5gc/amf

Source published

25 Jun 2026 18:43:15 UTC

Source modified

25 Jun 2026 19:45:15 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

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.