Vulnerability-Lookup

CVE-2026-42081 (GCVE-0-2026-42081)

Vulnerability from cvelistv5 – Published: 2026-05-27 15:59 – Updated: 2026-05-27 17:56

Title

free5GC: UE Security Capability bypass on NGAP PathSwitchRequest

Summary

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.

Severity

6.1 (Medium)


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

SSVC

Exploitation: poc Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-05-27 17:55 UTC

CWE

CWE-358 - Improperly Implemented Security Check for Standard

Assigner

GitHub_M CNA under the mitre root

CNA scorecard C 72/100 over 7730 records in the last 180 days details

References

1 reference

URL	Tags
https://github.com/free5gc/free5gc/security/advis…	x_refsource_CONFIRM

Impacted products

1 product

Vendor	Product	Version	CPE status
free5gc	free5gc	Affected: < 4.2.2	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-42081

Vulnerability from fkie_nvd - Published: 2026-05-27 17:16 - Updated: 2026-10-14 20:10

Severity

6.1 (Medium) - CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:L
7.1 (High) - CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/free5gc/free5gc/security/advisories/GHSA-77x9-rf64-92gv	Exploit, Vendor Advisory
	134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/free5gc/free5gc/security/advisories/GHSA-77x9-rf64-92gv	Exploit, Vendor Advisory

Impacted products

	Vendor	Product	Version
	free5gc	free5gc	*

JSON

To clipboard

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          "product": "free5gc",
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GHSA-77X9-RF64-92GV

Vulnerability from github – Published: 2026-05-07 01:53 – Updated: 2026-06-08 23:46

Summary

Free5GC AMF Bypasses UE Security Capabilities on NGAP PathSwitchRequest

Details

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:

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:

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.
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.
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:

Start Free5GC full stack and register a UE through a gNB (NG Setup → Registration → PDU Session Setup).
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.
Send a PathSwitchRequest with nRintegrityProtectionAlgorithms = 0x0000 (all integrity algorithms set to not supported). The AMF responds with PathSwitchRequestAcknowledge.
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).

Severity

6.1 (Medium)


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

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{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/free5gc/amf"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "1.4.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-42081"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-358"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-07T01:53:47Z",
    "nvd_published_at": "2026-05-27T17:16:34Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\nThe 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 \u00a76.7.3.1. A malicious gNB can overwrite the AMF\u0027s 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.\n\n### Details\n**Affected File:** `amf/internal/ngap/handler.go` \u2014 `handlePathSwitchRequestMain` function\n\n**Root Cause:**\n\nWhen 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:\n\n```go\nif uESecurityCapabilities != nil {\n    amfUe.UESecurityCapability.SetEA1_128_5G(uESecurityCapabilities.NRencryptionAlgorithms.Value.Bytes[0] \u0026 0x80)\n    amfUe.UESecurityCapability.SetEA2_128_5G(uESecurityCapabilities.NRencryptionAlgorithms.Value.Bytes[0] \u0026 0x40)\n    amfUe.UESecurityCapability.SetEA3_128_5G(uESecurityCapabilities.NRencryptionAlgorithms.Value.Bytes[0] \u0026 0x20)\n    amfUe.UESecurityCapability.SetIA1_128_5G(uESecurityCapabilities.NRintegrityProtectionAlgorithms.Value.Bytes[0] \u0026 0x80)\n    amfUe.UESecurityCapability.SetIA2_128_5G(uESecurityCapabilities.NRintegrityProtectionAlgorithms.Value.Bytes[0] \u0026 0x40)\n    amfUe.UESecurityCapability.SetIA3_128_5G(uESecurityCapabilities.NRintegrityProtectionAlgorithms.Value.Bytes[0] \u0026 0x20)\n}\n```\n\n**3GPP TS 33.501 \u00a76.7.3.1 requires three actions, none of which are implemented:**\n\n1. **Verification (SHALL):** \"The AMF shall verify that the UE\u0027s 5G security capabilities received from the target gNB/ng-eNB are the same as the UE\u0027s 5G security capabilities that the AMF has locally stored.\"\n   \u2192 Not implemented. The AMF unconditionally overwrites stored values.\n\n2. **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.\"\n   \u2192 Not implemented. The PathSwitchRequestAcknowledge contains the corrupted values.\n\n3. **Logging (SHALL):** \"The AMF shall support logging capabilities for this event and may take additional measures, such as raising an alarm.\"\n   \u2192 Not implemented. No mismatch detection or logging exists.\n\n**Propagation:**\n\nThe corrupted values are propagated in:\n- **PathSwitchRequestAcknowledge:** Contains corrupted UESecurityCapabilities (demonstrated in pcap)\n- **Subsequent HandoverRequest messages:** AMF sends corrupted capabilities to target gNBs\n\nPer TS 38.413 \u00a78.4.2.4, 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.\n\n### PoC\n**Environment:**\n- Free5GC v4.2.1 AMF (Docker container) with full NF stack (NRF, AUSF, UDM, UDR, NSSF, PCF, SMF, UPF)\n- UERANSIM v3.2.7 gNB with custom inspection-tool extension\n- tshark for packet capture\n\n**Reproduction Steps:**\n\n1. Start Free5GC full stack and register a UE through a gNB (NG Setup \u2192 Registration \u2192 PDU Session Setup).\n\n2. 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.\n\n3. Send a PathSwitchRequest with `nRintegrityProtectionAlgorithms = 0x0000` (all integrity algorithms set to not supported). The AMF responds with PathSwitchRequestAcknowledge.\n\n4. Observe that the PathSwitchRequestAcknowledge contains `nRintegrityProtectionAlgorithms = 0x0000` \u2014 the corrupted values are propagated back.\n\n**Observed Result (from pcap capture):**\n\n| Packet | Message | nRintegrityProtectionAlgorithms |\n|--------|---------|-------------------------------|\n| #20 | HandoverRequest (AMF\u2192gNB) | `0xe000` (NIA1 \u2713 NIA2 \u2713 NIA3 \u2713) \u2014 **baseline** |\n| #30 | PathSwitchRequest (gNB\u2192AMF) | `0x0000` \u2014 **poison** |\n| #47 | PathSwitchRequestAcknowledge (AMF\u2192gNB) | `0x0000` (NIA1 \u2717 NIA2 \u2717 NIA3 \u2717) \u2014 **corrupted** |\n\n### Impact\n**Availability (HIGH):** A malicious gNB can send a single PathSwitchRequest message to corrupt the AMF\u0027s stored UE security capabilities for any UE. All subsequent inter-gNB handovers for the affected UE are expected to fail (per TS 38.413 \u00a78.4.2.4), resulting in denial-of-service that persists until the UE performs a new registration.\n\n**Integrity (LOW):** The AMF\u0027s internal UE security context is corrupted with attacker-controlled values. These corrupted values are propagated to other network elements via PathSwitchRequestAcknowledge and HandoverRequest messages.\n\n**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).",
  "id": "GHSA-77x9-rf64-92gv",
  "modified": "2026-06-08T23:46:37Z",
  "published": "2026-05-07T01:53:47Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/free5gc/free5gc/security/advisories/GHSA-77x9-rf64-92gv"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-42081"
    },
    {
      "type": "WEB",
      "url": "https://github.com/free5gc/amf/blame/v1.4.3/internal/ngap/handler.go"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/free5gc/free5gc"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Free5GC AMF Bypasses UE Security Capabilities on NGAP PathSwitchRequest"
}

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Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

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CVE-2026-42081 (GCVE-0-2026-42081)

FKIE_CVE-2026-42081

GHSA-77X9-RF64-92GV

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