CVE-2026-120678 in C Driver
Summary
by MITRE • 11/03/2026
A memory management flaw in the MongoDB C Driver's handling of compressed responses may cause the client library to hold on to memory that is never released. An unauthenticated party that controls the database endpoint a client application connects to may cause repeated, unbounded memory growth in that application, which may result in the application becoming unavailable. No credentials, transport security settings, or user interaction are required.
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Analysis
by VulDB Data Team • 11/03/2026
The vulnerability identified involves a critical memory management flaw within the MongoDB C Driver, specifically affecting its processing of compressed database responses. This issue stems from an improper handling mechanism where allocated memory buffers associated with decompressed data are not correctly released back to the system after use. In standard software operation, when a client application requests data from a database server, the driver receives the response, potentially compresses it for transmission efficiency, and then decompresses it on the client side before passing the usable data to the application logic. The flaw occurs during this lifecycle, where the memory allocated for the compressed payload or its intermediate states is retained rather than freed once the operation completes. This results in a classic memory leak scenario within the driver's internal state management structures.
From an operational perspective, this defect allows for unbounded memory growth on any client application utilizing the affected version of the MongoDB C Driver. Since no authentication credentials are required to trigger this behavior, an attacker does not need valid user accounts or elevated privileges to exploit the vulnerability. Furthermore, transport security settings such as TLS encryption do not mitigate the risk because the flaw exists in the post-decryption processing logic on the client side. The attack vector is straightforward: an unauthenticated party controlling a database endpoint can send specifically crafted compressed responses that trigger the memory retention bug repeatedly. Each interaction causes the application to consume additional system memory without releasing it, leading to a gradual but steady increase in resource consumption over time.
The impact of this vulnerability is primarily denial of service through resource exhaustion. As the client application continues to process these maliciously crafted responses, its resident set size grows continuously until it exhausts available physical RAM or swap space. Once system memory limits are reached, the operating system may begin killing processes or the application itself may crash due out-of-memory errors. This renders the affected service unavailable to legitimate users, disrupting business operations and potentially causing data loss if transactions were in progress at the time of failure. The severity is heightened by the fact that user interaction is not required; automated scripts can repeatedly exploit this flaw with minimal effort, making it a high-risk vector for persistent availability attacks against MongoDB-dependent infrastructure.
This vulnerability aligns with CWE-401, which describes Missing Release of Memory after Effective Lifetime, and falls under the broader category of resource exhaustion flaws often associated with CWE-770: Allocation of Resources Without Limits or Throttling. In terms of adversarial tactics, this exploit maps to MITRE ATT&CK technique T1498: Network Denial of Service, specifically involving resource consumption attacks that degrade service availability without necessarily compromising data integrity or confidentiality. The lack of authentication requirements places it in a high-severity category for remote exploitation scenarios where the database endpoint is accessible over the network.
Mitigation strategies must focus on immediate patching and architectural safeguards. Organizations should update their MongoDB C Driver dependencies to versions that include fixes for this memory management issue, ensuring that all client applications are running patched libraries. In environments where immediate patching is not feasible, implementing rate limiting at the database proxy or load balancer level can help mitigate the frequency of requests sent to vulnerable endpoints, thereby slowing down the rate of memory exhaustion. Additionally, deploying monitoring solutions that track application memory usage trends can provide early warning signs of such attacks, allowing administrators to restart affected services before total system failure occurs. Long-term resilience requires enforcing strict input validation and compression limits on database responses to prevent excessively large or malformed payloads from being processed by client drivers.