# CVE-2026-40249: free5gc UDR fail-open request handling in PolicyDataSubsToNotifySubsIdPut may allow unintended subscription updates after input errors

> Attackers can modify Policy Data notification subscriptions in free5GC UDR by exploiting fail-open error handling that continues execution despite invalid input.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 16 Apr 2026
- **Updated:** 18 Apr 2026
- **Also known as:** GHSA-gx38-8h33-pmxr, GO-2026-5407

## What is CVE-2026-40249?

CVE-2026-40249 is a medium-severity vulnerability in Free5gc Free5gc, published on 16 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

free5GC is an open-source implementation of the 5G core network. In versions 4.2.1 and below of the UDR service, the PUT handler for updating Policy Data notification subscriptions at /nudr-dr/v2/policy-data/subs-to-notify/{subsId} does not return after request body retrieval or deserialization errors. Although HTTP 500 or 400 error responses are sent, execution continues and the processor is invoked with a potentially uninitialized or partially initialized PolicyDataSubscription object. This fail-open behavior may allow unintended modification of existing Policy Data notification subscriptions with invalid or empty input, depending on downstream processor and storage behavior. A patched version was not available at the time of publication.

Weakness: CWE-754 (Improper Check for Unusual or Exceptional Conditions), CWE-636 (Not Failing Securely)

## Which versions are affected by CVE-2026-40249?

3 open source packages ship an affected version, including github.com/free5gc/udr. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/free5gc/udr` | Go | All versions | None |
| `github.com/free5gc/udr` | Go | All versions to 1.4.2 | None |
| `github.com/free5gc/udr` | Go | All versions to 1.4.2 | None |

Products: Free5gc Free5gc.

## How do I fix CVE-2026-40249?

No fix published yet.

## Is CVE-2026-40249 being exploited?

There is no known exploitation of CVE-2026-40249 in the wild and no public exploit code.

## Other vulnerabilities in Free5gc Free5gc

- [CVE-2026-44327](https://insights.sbomify.com/CVE-2026-44327/): free5GC: NEF nnef-oam route group is unauthenticated; no-token requests reach the OAM handler (critical 10.0)
- [CVE-2026-44329](https://insights.sbomify.com/CVE-2026-44329/): free5GC's SMF UPI management interface lacks auth middleware; unauthenticated topology read/write requests reach handlers (critical 10.0)
- [CVE-2026-44330](https://insights.sbomify.com/CVE-2026-44330/): free5GC's NEF nnef-pfdmanagement API is unauthenticated; forged bearer tokens can read PFD data and create/delete PFD subscriptions (critical 10.0)
- [CVE-2025-63679](https://insights.sbomify.com/CVE-2025-63679/): Memory corruption in n/a (critical 9.8)
- [CVE-2026-44315](https://insights.sbomify.com/CVE-2026-44315/): free5GC's NEF 3gpp-pfd-management API is unauthenticated; forged bearer tokens can create, read, and delete PFD transactions (critical 9.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-40249 and fix it if it is affected.

What it is: CVE-2026-40249 is a medium-severity vulnerability in Free5gc Free5gc, published on 16 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-40249 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/free5gc/udr (Go): affected all versions; no fix listed
- github.com/free5gc/udr (Go): affected all versions up to 1.4.2; no fix listed
- github.com/free5gc/udr (Go): affected all versions up to 1.4.2; no fix listed

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-40249/ (Markdown: https://insights.sbomify.com/CVE-2026-40249/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40249
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40249
- OSV: https://osv.dev/vulnerability/CVE-2026-40249

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-40249/
Summaries are generated and may contain mistakes; the official description above is the record.