CVE-2026-114653 in C# Driver
Summary
by MITRE • 10/23/2026
A client-side encryption schema construction component in the MongoDB C# Driver places caller-supplied field identifiers into a position that is interpreted as a pattern expression, without normalizing or validating them. As a result, an application that designates certain fields for client-side field-level encryption may have the protection silently fail to apply, so data intended to be encrypted is stored and returned in cleartext; conversely, the rule may apply more broadly than intended. No user action is required to cause the condition, and any party with ordinary read access to the stored data — without possession of the encryption keys — can observe the unprotected values.
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Analysis
by VulDB Data Team • 10/23/2026
The vulnerability identified within the MongoDB C# Driver represents a critical failure in input validation logic specifically affecting the client-side field-level encryption schema construction component. This flaw arises from an improper neutralization of special elements used in pattern expressions, where caller-supplied field identifiers are inserted directly into query structures without adequate sanitization or normalization. In the context of MongoDB's query language, certain characters and sequences hold specific syntactic meaning for regular expression matching or key specification. When user-controlled input is treated as a literal string rather than being escaped or validated against expected formats, it can be interpreted by the database engine as part of an active pattern expression. This misinterpretation allows attackers to manipulate the scope and target of encryption rules through crafted field names that exploit these syntactic ambiguities.
The operational impact of this vulnerability is severe due to its silent nature. Typically, security failures in encryption libraries result in explicit errors or exceptions that alert administrators to configuration issues. However, in this scenario, the application does not throw an error when the schema construction fails as intended; instead, it proceeds with a flawed understanding of which fields are protected. Consequently, data designated for client-side field-level encryption may be stored and returned in cleartext without any indication that the protection mechanism has failed. This silent failure creates a false sense of security, leading organizations to believe their sensitive data is encrypted when it is actually exposed. Conversely, if an attacker can inject patterns that match unintended fields, the encryption rules may apply more broadly than intended, potentially causing performance degradation or logical errors in applications relying on specific field structures.
From a threat modeling perspective, this vulnerability aligns with CWE-79, which covers Improper Neutralization of Input During Web Page Generation, although adapted here for database query construction rather than HTML output. It also relates to CWE-20, the improper input validation category, as the driver fails to restrict or validate the format of field identifiers before embedding them into encryption schemas. In terms of attack vectors and techniques, this flaw facilitates data exposure that can be exploited via ATT&CK technique T1537, specifically under the sub-category of Data Encrypted for Transit if the cleartext is transmitted over a network, or more accurately T1048, Exfiltration Over Alternative Protocol, as attackers with read access to the database can harvest unencrypted sensitive data. The lack of user action required to trigger this condition means that any interaction involving schema definition or field selection based on dynamic input poses a risk.
Mitigation strategies must focus on rigorous input validation and defense-in-depth principles. Developers should implement strict allow-listing for field identifiers, ensuring they conform to expected naming conventions such as alphanumeric characters only, thereby preventing the injection of special regex metacharacters. Additionally, utilizing parameterized queries or dedicated API methods that abstract away direct string concatenation in schema definitions can reduce the risk of syntactic confusion between data and code-like structures. It is also critical to implement monitoring and logging for encryption operations to detect anomalies where expected fields are not encrypted as per policy. Organizations should review their current usage of the MongoDB C# Driver, particularly any dynamic generation of field names based on user input or external configuration sources, and apply patches provided by the driver maintainers that address this validation gap. Regular security audits focusing on data classification and encryption coverage can help identify instances where cleartext storage has occurred due to such silent failures.