CVE-2026-120684 in C Driver
Summary
by MITRE • 11/03/2026
A memory-initialization flaw in the legacy GridFS file handling of the MongoDB C Driver can cause uninitialized process memory to be treated as valid file content and stored on the server. A database user holding ordinary write access to a shared storage area can arrange conditions under which an application later appends to such a file and writes that memory into records the same user is permitted to read, which may result in unintended disclosure of sensitive information from the application's process, including credentials.
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Analysis
by VulDB Data Team • 11/03/2026
The vulnerability identified as CVE-2019-20345 represents a critical security flaw within the legacy GridFS file handling mechanism of the MongoDB C Driver, specifically affecting versions prior to 1.7.0 on Linux and macOS platforms. This issue stems from improper memory initialization practices during the processing of large files or specific chunking operations inherent to the GridFS protocol. When an application utilizes this driver to store data via GridFS, a segment of process memory is allocated for buffering file contents but fails to be properly zeroed out before being written to disk if certain conditions regarding buffer size and alignment are met. Consequently, any residual data previously held in that memory location remains intact within the newly created or updated file chunks stored on the server's storage subsystem. This behavior constitutes a classic instance of information disclosure through uninitialized memory exposure, aligning with CWE-908 which describes the use of uninitialized resource values leading to unintended information leakage.
The operational impact of this vulnerability is severe because it allows for the potential exfiltration of sensitive data from the application process running on the server hosting MongoDB. An attacker who possesses ordinary write access to a shared storage area within the database can exploit this flaw by uploading files that trigger the memory initialization bug. Once such a file is stored, subsequent operations where an authorized user appends additional content to the same GridFS file or reads its contents may inadvertently expose the uninitialized memory segments. These segments often contain remnants of previous application activities, including but not limited to authentication credentials, session tokens, private keys, and other proprietary data structures that were previously loaded into RAM by the application before being overwritten partially by new input. This scenario effectively bypasses standard access controls because the attacker does need elevated privileges; they only require write permissions to trigger the storage of sensitive memory dumps which can then be read back or accessed through normal file retrieval operations if the user has appropriate read rights on that specific resource.
From a threat modeling perspective, this vulnerability facilitates data exfiltration and credential theft without requiring direct exploitation of buffer overflow conditions typically associated with more complex attacks. It leverages the persistence mechanism of MongoDB to store sensitive artifacts in plain text within database files, making them accessible through standard query operations if access control policies are not strictly enforced per collection or bucket. This aligns with MITRE ATT&CK technique T1005 which involves data from local system retrieval and potentially T1530 for data from cloud storage objects if the underlying infrastructure is virtualized or containerized in a way that exposes these files to other processes. The flaw highlights the risks associated with legacy code paths in widely used database drivers, where performance optimizations may inadvertently sacrifice security hygiene such as memory sanitization.
Mitigation strategies must focus on immediate software updates and architectural reviews. Organizations running MongoDB C Driver versions earlier than 1.7.0 should upgrade to version 1.7.0 or later immediately, as this release includes the necessary fixes for proper memory initialization in GridFS operations. For environments where upgrading is not instantly feasible, administrators should enforce strict least-privilege access controls on database collections and buckets, ensuring that write-only users cannot inadvertently create files readable by others unless explicitly intended. Additionally, application-level mitigations include avoiding the use of legacy GridFS implementations for storing sensitive data until patches are applied and implementing rigorous input validation to minimize the surface area for memory manipulation attacks. Regular auditing of database permissions and monitoring for unusual patterns in file uploads can also help detect potential exploitation attempts before significant data loss occurs.