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CVE-2026-55068 – NF Registration Poisoning / Signaling Traffic Redirection – free5GC NRF (≤ 4.2.2)

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Summary

CVE-2026-55068 is a critical improper input validation vulnerability (CWE-20) in the Network Repository Function (NRF) of free5GC, an open-source 5G core network implementation. The NRF’s RegisterNFInstance handler accepts Network Function (NF) profiles without enforcing 3GPP TS 29.510 field constraints, allowing an attacker with access to the Service-Based Interface (SBI) to register fraudulent NF profiles with attacker-controlled service endpoints. The issue is rated CRITICAL with a CVSS v4.0 base score of 9.3.

Technical details

  • Root cause: the NRF endpoint PUT /nnrf-nfm/v1/nf-instances/{nfInstanceID} accepts NF Profiles without enforcing UUID format for nfInstanceId, valid nfStatus enum values, heartBeatTimer range limits, presence of mandatory profile fields, or address constraints on nfServices.ipEndPoints.
  • Trigger condition: an attacker with network access to the SBI can submit a crafted NF registration request; malformed and malicious profiles are accepted and persisted (returning HTTP 200/201) rather than being rejected.
  • Attack vector: network-based, no privileges or user interaction required.
  • Impact: the invalid/malicious NF profiles are stored in the NRF’s backing datastore and returned to legitimate NFs via NFDiscover, enabling "NF Registration Poisoning." Attacker-controlled endpoints can be advertised as legitimate network functions, allowing interception of control-plane signaling, harvesting of OAuth2 credentials, and denial of service to subscribers relying on NFs that trust the NRF.

Affected software

  • free5GC (github.com/free5gc/free5gc) versions prior to 4.2.3
  • free5GC NRF component (github.com/free5gc/nrf) versions prior to 1.4.5

Severity

CVSS v4.0 Base Score: 9.3 (Critical)
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate: Upgrade free5GC to version 4.2.3 or later, and the NRF component to v1.4.5 or later, which add validation for UUID format, enum values, numeric ranges, mandatory fields, and IP endpoint constraints on NF registration requests.
  • If patching is not immediately possible: restrict network access to the SBI (Service-Based Interface) to trusted network functions only, place the NRF behind strict network segmentation/firewalling so untrusted hosts cannot reach nnrf-nfm endpoints, and monitor NF registrations/NFDiscover results for unexpected or malformed NF profiles.

References

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