CVE-2026-55068 in Free5GC
Summary
by MITRE • 08/28/2026
free5GC is an open-source implementation of the 5G core network. In 4.2.2 and earlier, the NRF RegisterNFInstance handler at PUT /nnrf-nfm/v1/nf-instances/{nfInstanceID} accepts NF Profiles without enforcing UUID format, nfStatus enum values, heartBeatTimer ranges, mandatory profile fields, or nfServices.ipEndPoints address constraints. The invalid profiles are persisted in the MongoDB NfProfile collection and returned by NFDiscover, allowing an attacker with SBI access to advertise attacker-controlled network-function endpoints and redirect control-plane signaling. This can expose credentials and signaling, alter service discovery integrity, and deny service across network functions that trust the NRF. This issue is fixed in version 4.2.3.
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Analysis
by VulDB Data Team • 08/28/2026
The vulnerability identified within free5GC versions prior to 4.2.3 represents a critical failure in input validation at the Network Repository Function interface, specifically affecting the RegisterNFInstance handler exposed via the PUT /nnrf-nfm/v1/nf-instances/{nfInstanceID} endpoint. As an open-source implementation of the 5G core network, free5GC relies on strict adherence to 3GPP standards for service-based architecture interactions. The NRF serves as a central directory and discovery function within the 5G core, maintaining profiles of various Network Functions such as AMF, SMF, and UPF. By accepting NF Profiles without enforcing UUID format compliance, valid nfStatus enum values, proper heartBeatTimer ranges, mandatory profile fields, or correct ipEndPoints address constraints, the system allows for the injection of malformed data that violates fundamental structural integrity requirements defined in industry standards such as CWE-20 Improper Input Validation and CWE-749 Exposed Dangerous Method.
The operational impact of this flaw is severe due to the persistence mechanism employed by free5GC. Invalid profiles are not rejected but are instead stored directly into the MongoDB NfProfile collection, which serves as the authoritative source for service discovery queries. This design decision enables an attacker with access to the Service-Based Interface to register malicious or malformed network function entries that appear valid within the database structure despite lacking proper semantic correctness. When other network functions perform NFDiscover operations, they retrieve these compromised profiles from the NRF and proceed to establish connections based on the advertised endpoints. This effectively allows for service discovery integrity compromise, where the trust model of the 5G core is subverted by injecting rogue entries that redirect control-plane signaling traffic.
From a tactical perspective, this vulnerability aligns with MITRE ATT&CK techniques related to Resource Hijacking and Command and Control via Infrastructure Modifications. An attacker can exploit this misconfiguration to perform man-in-the-middle attacks or denial of service against specific network functions. By advertising attacker-controlled endpoints, the adversary can intercept sensitive signaling messages, potentially exposing user credentials and session data that traverse the control plane. Furthermore, because subsequent NFs trust the NRF for discovery results, the integrity of the entire service mesh is undermined. This can lead to widespread disruption as legitimate services attempt to connect to non-existent or maliciously controlled endpoints, resulting in a denial of service across multiple network functions that rely on accurate registry data for their operational continuity.
Mitigation strategies must prioritize immediate patching and architectural review. The primary remediation is upgrading free5GC to version 4.2.3 or later, where the RegisterNFInstance handler has been hardened to enforce strict validation rules consistent with 3GPP specifications. In environments where immediate upgrade is not feasible, network segmentation should be implemented to restrict access to the NRF Service-Based Interface exclusively to authorized internal services using mutual TLS authentication and IP whitelisting. Additionally, database-level monitoring can detect anomalous writes to the NfProfile collection that deviate from expected schema patterns, providing an additional layer of defense against exploitation attempts until the underlying software vulnerability is resolved.