CVE-2026-40249

A fail-open request handling flaw in the UDR service causes the /nudr-dr/v2/policy-data/subs-to-notify/{subsId} PUT handler to continue processing requests even after request body retrieval or deserialization errors.

This may allow unintended modification of existing Policy Data notification subscriptions with invalid, empty, or partially processed input, depending on downstream processor behavior.

Details

The endpoint PUT /nudr-dr/v2/policy-data/subs-to-notify/{subsId} is intended to update an existing Policy Data notification subscription only after the HTTP request body has been successfully read and parsed into a valid PolicyDataSubscription object. [file:93]

In the free5GC UDR implementation, the function HandlePolicyDataSubsToNotifySubsIdPut inNFs/udr/internal/sbi/api_datarepository.go does not terminate execution after input-processing failures. [file:93]

The request flow is:

1. The handler calls c.GetRawData() to read the HTTP request body. [file:93]
2. If GetRawData() fails, the handler sends an HTTP 500 error response, but does not return. [file:93]
3. The handler then calls openapi.Deserialize(policyDataSubscription, reqBody, "application/json"). [file:93]
4. If deserialization fails, the handler sends an HTTP 400 error response, but again does not return. [file:93]
5. Execution continues and the handler still invokes s.Processor().PolicyDataSubsToNotifySubsIdPutProcedure(c, subsId, policyDataSubscription). [file:93]

As a result, the endpoint operates in a fail-open manner: request processing may continue after fatal input validation or body handling errors, instead of being safely aborted. [file:93]

The issue is compounded by the handler's deserialization call, which passes policyDataSubscription directly to openapi.Deserialize(...) instead of passing a pointer to the destination object. This inconsistent usage further increases the risk that request processing continues with an empty, partially initialized, or otherwise unintended subscription object. [file:93]

This differs from safer handlers in the same file, which use a helper pattern that explicitly returns on body read or deserialization failure before calling the corresponding processor routine. [file:93]

Security Impact

This issue affects a write-capable API that updates Policy Data notification subscriptions identified by subsId. [file:93]
Because execution continues after body read or parsing failure, the processor may receive an uninitialized, partially initialized, or otherwise unintended PolicyDataSubscription object for persistence. [file:93]

The exact runtime impact depends on downstream processor behavior and storage validation. [file:93]
At minimum, this is a security-relevant robustness flaw that can lead to inconsistent request handling or unintended modification attempts; under certain runtime conditions it may allow updates that should not be processed after an input error. [file:93]

Reproduction Status

The code path has been statically confirmed. [file:93] A complete runtime proof of unintended subscription modification after
GetRawData() or deserialization failure has not yet been established. [file:93]

CVE-2026-40249 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

The handler should immediately terminate after sending an error response for body read or deserialization failure. [file:93]

A minimal fix is to add missing return statements in HandlePolicyDataSubsToNotifySubsIdPut and pass a pointer to the destination
object during deserialization: [file:93]

reqBody, err := c.GetRawData()
if err != nil {
    logger.DataRepoLog.Errorf("Get Request Body error: %+v", err)
    pd := openapi.ProblemDetailsSystemFailure(err.Error())
    c.Set(sbi.IN_PB_DETAILS_CTX_STR, pd.Cause)
    c.JSON(http.StatusInternalServerError, pd)
    return
}

err = openapi.Deserialize(&policyDataSubscription, reqBody, "application/json")
if err != nil {
    logger.DataRepoLog.Errorf("Deserialize Request Body error: %+v", err)
    pd := util.ProblemDetailsMalformedReqSyntax(err.Error())
    c.Set(sbi.IN_PB_DETAILS_CTX_STR, pd.Cause)
    c.JSON(http.StatusBadRequest, pd)
    return
}

1. What is CVE-2026-40249? CVE-2026-40249 is a medium-severity security vulnerability in github.com/free5gc/udr (go), affecting versions <= 1.4.2. No fixed version is listed yet.
2. How severe is CVE-2026-40249? CVE-2026-40249 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/udr are affected by CVE-2026-40249? github.com/free5gc/udr (go) versions <= 1.4.2 is affected.
4. Is there a fix for CVE-2026-40249? No fixed version is listed for CVE-2026-40249 yet. Monitor the advisory for updates and apply mitigations in the interim.
5. Is CVE-2026-40249 exploitable, and should I be worried? Whether CVE-2026-40249 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-2026-40249 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.