CVE-2026-114651 in C# Driver
Summary
by MITRE • 10/22/2026
A memory-handling weakness in the BSON deserialization component of the MongoDB C# Driver may cause data left over from previously processed content to be returned when specially crafted serialized input is parsed. An unauthenticated party able to supply serialized data to an application that maps certain primitive collection types can cause residual bytes from unrelated data processed earlier on the same execution thread to be surfaced as legitimate values. This can result in disclosure of a limited amount of information belonging to other requests or principals of the consuming application. No authentication or special privileges within the application are required.
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Analysis
by VulDB Data Team • 10/22/2026
The vulnerability described constitutes a critical memory safety flaw within the BSON deserialization logic of the MongoDB C# Driver, specifically affecting how primitive collection types handle buffer allocation and reuse during parsing operations. This issue stems from an improper initialization of internal data structures where previously allocated memory buffers are not fully cleared or overwritten before being repurposed for new deserialization tasks. When a specially crafted serialized input is processed, the driver fails to zero out residual bytes that remain in these reused memory segments from prior execution contexts on the same thread. Consequently, instead of returning nulls or default values for missing fields, the parser inadvertently exposes stale data left over from earlier requests handled by the same application thread. This behavior creates a direct pathway for information leakage, as sensitive context-specific data can be misinterpreted as legitimate field values in subsequent operations.
From an operational perspective, this flaw enables unauthenticated attackers to extract confidential information belonging to other users or system processes without requiring any form of authentication or elevated privileges within the target application. The attack vector relies on the ability to supply crafted BSON payloads that trigger the specific deserialization path involving primitive collections such as lists or arrays of integers and strings. Because MongoDB drivers often utilize connection pooling and thread reuse for performance optimization, an attacker can exploit this race condition by sending requests in a manner that ensures their malicious payload is processed immediately after another user's sensitive data on the same worker thread. The result is the disclosure of limited but potentially high-value information, such as session tokens, internal identifiers, or other private fields, which are then surfaced as part of the response to the attacker’s request. This type of vulnerability aligns with CWE-200: Information Exposure and falls under the broader category of Improper Memory Handling often associated with CWE-134: Use of Externally-Controlled Format String in combination with memory management errors, though it is more accurately classified as a logical error in buffer initialization rather than a classic buffer overflow.
The impact extends beyond simple data disclosure to include potential integrity issues if the residual data influences application logic that relies on these fields for decision-making processes. For instance, if an internal flag or permission level is inadvertently populated with stale values from another user's context, it could lead to unauthorized access patterns or incorrect state transitions within the application layer. This scenario mirrors techniques observed in ATT&CK tactic T1530: Data from Cloud Storage Object and specifically relates to data exfiltration methods where attackers leverage memory corruption flaws to read sensitive information that should remain isolated per request scope. The lack of authentication requirements makes this vulnerability particularly dangerous, as it can be exploited remotely by any actor capable of interacting with the MongoDB interface exposed through the application.
Mitigation strategies must focus on ensuring strict isolation between deserialization contexts and enforcing rigorous initialization practices within the driver's codebase. Developers should verify that all memory buffers used for parsing are explicitly cleared or reallocated before being reused, thereby eliminating the possibility of residual data leakage. Upgrading to a patched version of the MongoDB C# Driver is the primary remediation step, as vendors typically address such issues by implementing proper zeroing routines and bounds checking during object mapping. Additionally, application-level defenses can include validating input lengths strictly against expected schemas and employing runtime protection mechanisms that detect anomalous memory access patterns. Security teams should also consider deploying Web Application Firewalls configured to inspect BSON payloads for irregularities in field sizes or unexpected data types that might indicate exploitation attempts. Regular security audits focusing on deserialization libraries are essential, as these components frequently serve as attack surfaces for complex logic flaws that bypass traditional perimeter defenses.