CVE-2026-106430 in C++ Driver
Summary
by MITRE • 10/08/2026
The MongoDB C++ Driver discards content after an embedded NUL byte in certain field and collection names accepted by the collection API. This can cause the driver and the calling application to interpret the same name differently. An authenticated actor who can influence a name passed by an affected application can cause the application to read distinct values from an unintended field or rename an unintended collection. These operations use the application's existing database credentials.
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Analysis
by VulDB Data Team • 10/08/2026
The MongoDB C++ Driver contains a critical input handling flaw where it fails to properly validate string boundaries for embedded NUL bytes within field and collection names submitted through the collection API. In many programming environments, particularly those rooted in C or C++, strings are traditionally null-terminated, meaning processing often stops at the first zero byte encountered. However, MongoDB's internal data structures and wire protocol support arbitrary binary content, including NUL characters, as valid parts of identifiers under specific conditions. The vulnerability arises because the driver truncates these names upon encountering an embedded NUL byte during parsing or transmission preparation, while the server may interpret the full string including the NUL character depending on how it is processed in subsequent operations. This discrepancy creates a state divergence between the client-side application logic and the database engine's interpretation of identifiers.
This technical flaw leads to significant security implications regarding data integrity and access control bypasses. An authenticated attacker who has the ability to influence or inject specific field names or collection names into queries executed by an affected application can exploit this inconsistency. For instance, if a developer constructs a query using a user-supplied string that contains a NUL byte followed by malicious content, the driver might truncate the name before sending it to the database, while the server processes the full identifier differently in other contexts or when accessed via different drivers. This allows an attacker to trick the application into reading data from unintended fields or renaming collections that were not originally targeted. Since these operations are performed using the application's existing database credentials, the attack leverages legitimate authentication tokens, making it difficult for standard intrusion detection systems to distinguish between authorized administrative actions and malicious exploitation attempts.
From a classification perspective, this vulnerability aligns with CWE-697, which describes incorrect comparison in software logic, specifically involving string handling discrepancies that lead to unintended behavior. It also relates closely to CWE-1345, an issue where the processing of input data leads to inconsistent states between components. In terms of offensive security frameworks such as MITRE ATT&CK, this technique falls under Tactic TA0006 (Credential Access) and Technique T1078 (Valid Accounts), as it exploits valid credentials through manipulation of application logic rather than breaking authentication mechanisms directly. It can also be viewed as a form of injection where the payload is embedded within an identifier field to alter execution context, similar in concept to SQL injection but operating at the driver-level parsing layer instead of query syntax interpretation.
The operational impact extends beyond simple data leakage or misdirection. Because MongoDB relies heavily on precise key-value mappings for document structure and collection management, any ambiguity introduced by truncated names can lead to severe logical errors within applications that depend on strict schema adherence. Attackers could potentially escalate privileges if the application performs privilege checks based on truncated identifiers while granting access based on full identifiers elsewhere in the codebase. Furthermore, renaming unintended collections due to this parsing error can result in data loss or corruption of critical system metadata, disrupting business continuity and requiring complex recovery procedures.
Mitigation strategies must focus on rigorous input validation at both the application layer and potentially within custom driver wrappers before passing strings to the MongoDB C++ Driver APIs. Developers should explicitly sanitize all field names and collection identifiers by rejecting any string containing NUL bytes or other control characters that are not strictly required for business logic, adhering to a principle of least privilege regarding identifier composition. Additionally, upgrading to patched versions of the MongoDB C++ driver where this parsing behavior has been corrected is essential if available. Organizations should also implement comprehensive logging and monitoring around database operations involving dynamic identifiers to detect anomalies in field access patterns or collection renaming events that deviate from expected application workflows. Regular security code reviews focusing on string handling practices across all layers interacting with the database are recommended to prevent similar discrepancies arising from assumptions about null-termination behavior versus binary-safe processing requirements.