CVE-2026-114650 in C# Driver
Summary
by MITRE • 10/22/2026
A flaw in the client-side encryption support of the MongoDB .NET/C# driver can cause data designated for client-side field-level encryption to be written without encryption. Under certain platform text-encoding configurations, an internal name conversion loses information, so the encryption layer fails to associate the operation with its configured encryption rules and the operation proceeds without an error being raised. An application user with the ability to write data through an affected application can therefore have sensitive fields persisted in plaintext, defeating the confidentiality guarantee that client-side encryption is intended to provide. No integrity or availability impact was observed.
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Analysis
by VulDB Data Team • 10/23/2026
The vulnerability described involves a critical failure in the MongoDB .NET/C# driver's implementation of client-side field-level encryption, specifically within its internal name conversion mechanisms under certain platform text-encoding configurations. Client-side encryption is designed to ensure that sensitive data fields are encrypted before they leave the application layer, thereby maintaining confidentiality even if the database infrastructure or storage backend is compromised. This security model relies on a strict mapping between logical field names in the application code and their corresponding encryption rules defined within the driver's configuration. The flaw arises when an internal name conversion process loses information due to specific encoding discrepancies, causing the encryption engine to fail in associating the write operation with its designated encryption policy. Consequently, instead of encrypting the data as intended, the system proceeds to persist the sensitive fields in plaintext without raising any error or warning, creating a silent failure mode that undermines the entire security posture of the application's data protection strategy.
From a technical perspective, this issue represents a classic case where encoding assumptions lead to information loss during string processing, which directly impacts security controls dependent on exact string matching for policy enforcement. The vulnerability allows an attacker with write access through the affected application to inject or modify records containing sensitive information that will be stored unencrypted in the database. This defeats the primary confidentiality guarantee provided by client-side encryption, as unauthorized parties who gain read access to the database can view this data in clear text. It is important to note that while the integrity and availability of the system remain unaffected, the breach of confidentiality is severe because it exposes proprietary or personal information that was explicitly protected by design. The silent nature of the failure means that standard error handling mechanisms will not alert administrators or developers to the misconfiguration, allowing the exposure to persist undetected for potentially long periods until a data audit reveals plaintext records where encrypted ones were expected.
This vulnerability aligns with CWE-200, which classifies it as an Information Exposure Vulnerability, specifically relating to unintended information disclosure through configuration errors or implementation flaws in security features. Furthermore, from the perspective of the MITRE ATT&CK framework, this flaw facilitates data exfiltration by compromising confidentiality controls, potentially falling under techniques related to unauthorized access to sensitive data or exploitation of misconfigured permissions and policies. The lack of error reporting exacerbates the risk, as it prevents immediate detection and remediation, allowing attackers who have compromised application credentials to harvest large volumes of unencrypted sensitive data without triggering alarms that would typically accompany failed encryption operations.
To mitigate this vulnerability, organizations must immediately update their MongoDB .NET/C# drivers to a version where this encoding-related name conversion flaw has been resolved. It is crucial to verify the platform text-encoding configurations used in production environments and ensure they are compatible with the driver's expectations for field name processing. Developers should implement rigorous testing procedures that include validation of encryption policies against various input strings, particularly those involving non-standard or complex character encodings, to detect silent failures early in the development lifecycle. Additionally, implementing database-level auditing logs can help identify instances where data was written without corresponding encryption markers, providing a secondary layer of detection for any remaining affected systems until all software components are fully patched and reconfigured according to best practices for secure client-side encryption deployment.