CVE-2026-88035 in C Driver
Summary
by MITRE • 09/10/2026
A size check in the client-side authentication path of the MongoDB C Driver can wrap around, so an unusually large user-name value is accepted and copied past the end of a small buffer. A party able to set the driver's connection settings may cause the application that embeds the driver to terminate unexpectedly. Reaching this code requires a build in which the optional external SASL authentication backend is present and a connection configured to use it.
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Analysis
by VulDB Data Team • 09/10/2026
The MongoDB C Driver contains a critical integer overflow vulnerability within its client-side authentication logic, specifically affecting the handling of user-name values during SASL (Simple Authentication and Security Layer) negotiations. This flaw arises from an insufficient size check that fails to account for potential arithmetic wraparound when calculating buffer requirements or validating input lengths. Consequently, if an attacker can influence the connection settings to present an unusually large username value, the driver may interpret this oversized integer as a smaller positive number due to overflow behavior. This misinterpretation leads to the allocation of a memory buffer that is significantly smaller than required for storing the actual user-name string.
When the application proceeds with copying the full-length username into this undersized buffer, it triggers a heap-based or stack-based buffer overflow depending on the specific implementation details and build configuration. The vulnerability specifically impacts builds where the optional external SASL authentication backend is enabled and configured to handle connections using that mechanism. Because the memory copy operation exceeds the bounds of the allocated space, adjacent memory structures are overwritten with data from the username input. This corruption typically results in immediate application instability, manifesting as a crash or termination due to segmentation faults or other fatal exceptions triggered by the corrupted state of the process memory.
From an operational impact perspective, this vulnerability primarily facilitates Denial of Service (DoS) attacks against applications embedding the MongoDB C Driver. An attacker who has the ability to set connection settings for the driver can exploit this flaw to cause unexpected termination of the host application. While buffer overflows often carry risks of arbitrary code execution, in this specific context involving client-side authentication paths and typical memory protection mechanisms like ASLR and DEP/NX bits, the most immediate and reliable outcome is service disruption rather than remote code execution. However, the potential for more severe exploitation cannot be entirely ruled out without further analysis of the surrounding heap layout or stack canaries, as overwritten data could theoretically influence control flow if specific conditions are met during subsequent memory operations.
This vulnerability aligns with CWE-190 (Integer Overflow or Wraparound) and CWE-787 (Out-of-bounds Write), reflecting both the root cause in arithmetic validation and the resulting memory corruption. In terms of attack vectors, it relates to MITRE ATT&CK techniques involving resource hijacking through denial of service, specifically leveraging input validation failures within authentication modules. The requirement for an attacker to set connection settings implies that this is not a remotely exploitable vulnerability over the network directly but rather requires local access or control over the application's configuration parameters prior to establishing the database connection.
Mitigation strategies should focus on immediate patching of the MongoDB C Driver to versions where integer overflow checks are properly implemented in the SASL authentication path. Developers must ensure that all input lengths, particularly those related to usernames and other credential fields, are validated against maximum allowable limits before any memory allocation or copy operations occur. Implementing strict bounds checking using safe string handling functions that verify length constraints is essential. Additionally, applications should employ defense-in-depth measures such as Address Space Layout Randomization (ASLR) and stack canaries to mitigate the impact of potential buffer overflows. Regular security audits focusing on input validation in authentication modules are recommended to prevent similar integer-related vulnerabilities from being introduced or overlooked in future updates.