free5gc UDR improper path validation allows unauthenticated creation and modification of Traffic Influence Subscriptions
Date: 2026-04
Affected: go/github.com/free5gc/udr
Attack vector: auth-bypass
Category: vulnerability-disclosure
Severity: High
CVE: CVE-2026-40248
CWE: CWE-285
CWE-636
CVSS: 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N)

### Summary An improper path validation vulnerability in the UDR service allows any unauthenticated attacker with access to the 5G Service Based Interface (SBI) to create or overwrite Traffic Influence Subscriptions by supplying an arbitrary value in place of the expected `subs-to-notify` path segment. ### Details The endpoint `PUT /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 `HandleApplicationDataInfluenceDataSubsToNotifySubscriptionIdPut`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, the request body is still parsed, and the handler calls `s.Processor().ApplicationDataInfluenceDataSubsToNotifySubscriptionIdPutProcedure(c, subscriptionId, &trafficInfluSub)`. 4. The processor creates or updates 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 `40


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