free5GC is an open-source implementation of the 5G core network. In versions 1.4.2 and below of the UDR service, the handler for deleting Traffic Influence Subscriptions checks whether the influenceId path segment equals subs-to-notify, but does not return after sending the HTTP 404 response when validation fails. Execution continues and the subscription is deleted regardless. An unauthenticated attacker with access to the 5G Service Based Interface can delete arbitrary Traffic Influence Subscriptions by supplying any value for the influenceId path segment, while the API misleadingly returns a 404 Not Found response. A patched version was not available at the time of publication.

Affected: Go: github.com/free5gc/udr

### Summary An improper path validation vulnerability in the UDR service allows any unauthenticated attacker with access to the 5G Service Based Interface (SBI) to delete Traffic Influence Subscriptions by supplying an arbitrary value in place of the expected `subs-to-notify` path segment.

### Details The endpoint `DELETE /nudr-dr/v2/application-data/influenceData/{influenceId}/{subscriptionId}` is intended to only operate on Traffic Influence Subscription resources when `influenceId` is exactly `subs-to-notify`.

In the free5GC UDR implementation, the path validation is present but ineffective because the handler does not return after sending the HTTP 404 response. The request handling flow is:

1. The function `HandleApplicationDataInfluenceDataSubsToNotifySubscriptionIdDelete` in `./free5gc_4-2-1/free5gc/NFs/udr/internal/sbi/api_datarepository.go` checks whether `influenceId != "subs-to-notify"`. 2. If the value is different, it calls `c.String(http.StatusNotFound, "404 page not found")`, **but it does not return afterwards**. 3. Execution continues and the handler still calls `s.Processor().ApplicationDataInfluenceDataSubsToNotifySubscriptionIdDeleteProcedure(c, subscriptionId)`. 4. The processor deletes the subscription identified by `subscriptionId` even though the path is invalid and the request should have been rejected.

As a result, an attacker can send a request to an invalid path, receive an apparent `404 page not found` response, and still successfully delete t…