A NoSQL injection weakness exists in the LINQ-to-aggregation translation layer of the MongoDB C# Driver. The vulnerability arises because unquoted constant GroupBy keys are not properly escaped, allowing special elements in application‑supplied values to be interpreted by the database as query logic rather than data. This can lead to unintended data being returned or query results being altered, representing a data exposure and manipulation risk (CWE-943).

Affected systems include the MongoDB C# Driver. No specific version range is provided in the data, but the issue is known to impact at least the version referenced by nuget.org/packages/MongoDB.Driver/3.11.1.

The CVSS score of 6.9 classifies this as a moderate severity vulnerability with unknown exploit probability (EPSS not available) and no listing in the CISA KEV catalog. The likely attack vector is through application‑supplied input that is incorporated into LINQ queries; a user who can control such input can exploit the injection flaw, potentially requiring authenticated access to the application. Because the injection occurs within the driver’s query translation, exploitation does not depend on database configuration but on the application's use of the driver.