CVE-2026-120956 in C Driver
Summary
by MITRE • 11/03/2026
The MongoDB C Driver does not validate the type or format of a namespace field returned by the server in a query response. A MongoDB endpoint that a client application connects to, without needing any credentials, can return a malformed value in that field. This causes the client application process to terminate, and can also cause the driver to read memory outside an allocated buffer and to send a small amount of the application's own uninitialized heap memory back to the endpoint in a follow-up command. The impact is limited to the process that embeds the driver.
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Analysis
by VulDB Data Team • 11/03/2026
The MongoDB C Driver contains a critical input validation deficiency regarding the handling of namespace fields within query responses received from server endpoints. This vulnerability arises because the client-side library fails to rigorously verify the type and format of data returned by the database before processing it for internal use. Specifically, when an application connects to a MongoDB instance without requiring authentication credentials, the server can be manipulated or misconfigured to return a malformed value in the namespace field of a query response. This lack of strict schema validation allows unexpected data structures to propagate through the driver's logic flow, triggering undefined behavior within the client process rather than being safely rejected or sanitized by the library itself.
The operational impact of this flaw is severe for any application embedding the MongoDB C Driver, as it can lead directly to a denial of service condition where the client application process terminates unexpectedly due to an unhandled exception or segmentation fault caused by invalid memory access patterns. Beyond simple crashes, the vulnerability poses significant data confidentiality risks because the driver may read memory outside of allocated buffers during its attempt to parse or utilize the malformed namespace field. This out-of-bounds read operation can expose sensitive internal state information held in adjacent heap memory locations that were not intended for external exposure.
Furthermore, the consequences extend beyond local process stability and privacy leakage into active data exfiltration capabilities. The vulnerability enables a scenario where uninitialized heap memory from the application is inadvertently sent back to the remote endpoint via subsequent commands issued by the driver. This mechanism effectively allows an unauthenticated attacker connected to the MongoDB server to receive fragments of the client's own private memory contents, potentially revealing cryptographic keys, session tokens, or other sensitive data structures residing in the process address space. The impact remains confined strictly to the local process that embeds the affected driver version, meaning remote code execution is not directly facilitated by this specific flaw, but rather information disclosure and service disruption are the primary vectors of exploitation.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation, as the core failure lies in the application's inability to correctly validate data received from an external source before processing it. Additionally, the out-of-bounds memory access component corresponds closely to CWE-125 Out-of-bounds Read and CWE-787 Out-of-bounds Write if write operations are triggered by subsequent malformed states. In terms of adversary tactics, this flaw supports ATT&CK technique T1005 Data from Local System which involves the collection of data stored on local systems for exfiltration purposes. The lack of authentication requirement further exacerbates the risk profile as it lowers the barrier to entry for potential attackers seeking to probe or exploit vulnerable instances deployed in public-facing environments without prior credential acquisition.
Mitigation strategies must prioritize immediate patching of the MongoDB C Driver to versions that implement strict type checking and format validation for all fields returned by server responses, particularly those related to namespace identifiers. Developers should ensure they are using supported releases where this input sanitization logic has been hardened against malformed inputs. In addition to software updates, organizations should enforce authentication requirements on all MongoDB endpoints wherever possible to prevent unauthenticated access that could trigger the specific conditions required for exploitation. Network segmentation and firewall rules restricting direct client-to-database communication can also serve as effective compensating controls to limit exposure until patches are fully deployed across infrastructure environments.