CVE-2026-84965 in C Driver
Summary
by MITRE • 09/03/2026
An integer wraparound in an allocation size calculation in the BSON library's JSON parsing code can cause a buffer to be released while a following copy operation still writes through the stale pointer. On builds where sizes are 32 bits, an unauthenticated party able to supply a sufficiently large JSON input to an application that links the library may cause that application to terminate unexpectedly, resulting in denial of service.
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Analysis
by VulDB Data Team • 09/05/2026
The vulnerability described involves a critical integer wraparound flaw within the BSON library's JSON parsing logic, specifically during memory allocation size calculations. This type of error typically occurs when a value exceeds the maximum limit representable by an unsigned 32-bit integer, causing it to overflow and wrap around to a small positive number rather than triggering an appropriate error or exception. In this specific context, the parser calculates the required buffer size based on input data but fails to validate that the calculated size remains within safe bounds before proceeding with memory allocation. Consequently, when an unauthenticated attacker supplies a JSON payload containing sufficiently large values, the arithmetic operation overflows, resulting in the allocation of a significantly smaller buffer than actually needed for the subsequent copy operations.
The operational impact stems directly from this mismatch between allocated and expected sizes. Once the undersized buffer is allocated, the library proceeds to parse the input data and performs memory copy operations that write beyond the boundaries of the newly allocated heap space. However, due to the specific implementation details mentioned in the description, there appears to be a sequence where the original or intermediate buffer state leads to premature release while subsequent writes are still attempted against stale pointers. This use-after-free condition allows an attacker to corrupt memory structures within the application process. The immediate consequence of this corruption is often catastrophic for the application's stability, leading to crashes and unexpected terminations. While such vulnerabilities can sometimes be leveraged for arbitrary code execution depending on heap layout and exploitation techniques, the primary documented impact here is a denial of service caused by the abrupt termination of the affected service or application.
From a classification perspective, this vulnerability aligns with CWE-190, which defines integer overflow or wraparound errors that can lead to other weaknesses such as buffer overflows or use-after-free conditions. The attack vector falls under CWE-20, improper input validation, as the system fails to adequately sanitize and validate the size parameters derived from untrusted JSON inputs before performing memory operations. In terms of adversary tactics, this aligns with MITRE ATT&CK techniques related to resource exhaustion for denial of service impacts, specifically leveraging software flaws to disrupt availability without requiring authentication credentials. The lack of authentication requirement makes this a high-severity remote vulnerability that can be exploited by any network-accessible attacker targeting the vulnerable component.
Mitigation strategies must focus on both immediate patching and long-term defensive coding practices. Organizations relying on the affected BSON library should immediately update to a patched version where developers have implemented rigorous bounds checking for all integer arithmetic operations related to memory allocation sizes. Developers should utilize safe math libraries or compiler flags that detect overflow conditions at runtime, ensuring that any calculation exceeding the maximum representable value triggers an error rather than wrapping around. Furthermore, implementing strict input validation on JSON payloads before they reach the parsing engine can prevent maliciously crafted inputs from reaching vulnerable code paths. For applications where immediate patching is not feasible, deploying web application firewalls or intrusion detection systems to detect and block unusually large JSON fields may provide a temporary layer of defense against exploitation attempts aimed at triggering this integer overflow condition.