Executive brief
A vulnerability in the free5GC Network Repository Function (NRF) allows an unauthenticated attacker to cause a service error by sending a specially crafted request to the token issuance endpoint. The NRF is a core component of 5G networks used for service discovery and authorization. While the system automatically recovers from these errors, a sustained attack could degrade performance, increase processing costs, and flood system logs with diagnostic data.
Technical details
A type-confusion vulnerability (CWE-843) exists in the `POST /oauth2/token` handler within `NFs/nrf/internal/sbi/api_accesstoken.go`. The parser uses Go reflection to map form-encoded body fields to the `models.NrfAccessTokenAccessTokenReq` struct but fails to validate that the input types match the destination field types. Specifically, it attempts to use `reflect.Value.Set()` to assign a `*models.PlmnId` type to fields expecting slices or different pointer types (e.g., `[]models.PlmnId`, `[]string`), leading to a runtime panic. While the Gin web framework catches these panics to prevent a full process crash, an unauthenticated attacker can repeatedly trigger this expensive failure path to cause resource exhaustion and log pollution. The issue is fixed in version 1.4.3.
Affected products
- free5GC nrf < 1.4.3
Timeline
- 2026-03-22: other: Vulnerability validated in lab environment
- 2026-05-07: advisory: GitHub Advisory published
- 2026-05-08: disclosed: Public disclosure