CVE-2026-41136

The HTTPUEContextTransfer handler in internal/sbi/api_communication.go does not include a default case in the Content-Type switch statement. When a request arrives with an unsupported Content-Type, the deserialization step is silently skipped, err remains nil, and the processor is invoked with a completely uninitialized UeContextTransferRequest object.

Details

In internal/sbi/api_communication.go, the HTTPUEContextTransfer function handles the Content-Type header with a switch statement that only covers application/json and multipart/related:

switch str[0] {
case applicationjson:
    err = openapi.Deserialize(ueContextTransferRequest.JsonData, requestBody, contentType)
case multipartrelate:
    err = openapi.Deserialize(&ueContextTransferRequest, requestBody, contentType)
// no default case
}

if err != nil {
    // skipped entirely when Content-Type is unsupported
    c.JSON(http.StatusBadRequest, rsp)
    return
}

s.Processor().HandleUEContextTransferRequest(c, ueContextTransferRequest)

This is inconsistent with the two analogous handlers in the same file, HTTPCreateUEContext and HTTPN1N2MessageTransfer, which both correctly include a default branch:

default:
    err = fmt.Errorf("wrong content type")

The fix is simply to add the same default case to HTTPUEContextTransfer.

PoC

With a free5GC deployment running, send a POST request to the UE context transfer endpoint using any unsupported Content-Type (e.g. text/plain):

curl -s -X POST "http://<AMF_IP>/namf-comm/v1/ue-contexts/<ueContextId>/transfer" \\
  -H "Content-Type: text/plain" \\
  -d '{"test":"data"}' \\
  -i

Expected (correct) behavior: 400 Bad Request from the SBI layer, rejecting the request due to unsupported Content-Type, consistent with HTTPCreateUEContext.

Actual (observed) behavior: The SBI-layer error check is bypassed and the processor is reached with an empty request object, returning:

HTTP/1.1 400 Bad Request
{"status": 400, "cause": "MANDATORY_IE_MISSING"}

The MANDATORY_IE_MISSING cause originates from the processor's internal validation, not from the SBI handler, confirming the processor was called with an uninitialized struct.

The endpoint is an inter-NF SBI API used during AMF-to-AMF UE context handover. It is not directly reachable from external UEs and requires access to the internal 5GC SBI network. The processor's secondary mandatory field validation prevents any unintended state modification, so there is no direct exploitability. However, the SBI handler layer is the intended first line of defense, relying on the processor to compensate for a missing input check increases fragility and violates defense in depth. Any future change to the processor's validation logic could inadvertently expose the system to processing completely empty request objects.

CVE-2026-41136 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.

Kodem intelligence

1. What is CVE-2026-41136? CVE-2026-41136 is a medium-severity security vulnerability in github.com/free5gc/amf (go), affecting versions <= 1.4.3. No fixed version is listed yet.
2. How severe is CVE-2026-41136? CVE-2026-41136 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/free5gc/amf are affected by CVE-2026-41136? github.com/free5gc/amf (go) versions <= 1.4.3 is affected.
4. Is there a fix for CVE-2026-41136? No fixed version is listed for CVE-2026-41136 yet. Monitor the advisory for updates and apply mitigations in the interim.
5. Is CVE-2026-41136 exploitable, and should I be worried? Whether CVE-2026-41136 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-41136 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.