CVE-2026-93765 in Mongoid
Summary
by MITRE • 09/18/2026
Mongoid contains an unsafe reflection weakness in the document persistence layer of its object-document mapping code. Input whose keys are passed through from an unauthenticated party by an embedding application can cause unintended internal method invocation instead of the intended array field update. This may result in unintended removal of stored records and in the embedding application becoming unresponsive.
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Analysis
by VulDB Data Team • 09/18/2026
The vulnerability identified within Mongoid, a popular Object-Document Mapping (ODM) library for Ruby applications interacting with MongoDB, represents a critical unsafe reflection weakness located specifically within its document persistence layer. This flaw stems from how the framework handles input data during object updates and insertions. In typical usage, developers expect that when an application receives user-supplied parameters to update a model instance, only the explicitly defined fields of that model are modified in the database. However, due to this reflection weakness, if an embedding application passes unauthenticated or insufficiently validated input keys directly into Mongoid's persistence methods without strict filtering, the library may interpret these keys not as data values for standard attributes but as instructions for internal method invocation. This behavior deviates significantly from the intended design where such inputs should result in simple array field updates or attribute assignments rather than triggering complex backend operations.
From a technical perspective, this issue exploits the dynamic nature of Ruby's reflection capabilities combined with Mongoid's flexible schema handling. When an attacker provides specially crafted input keys that mimic internal method names or specific structural identifiers recognized by the persistence layer, the ODM engine bypasses standard validation checks. Instead of treating these inputs as data to be stored in a specified field, the system executes them as commands against the document structure. This misinterpretation allows for unintended side effects during what should be routine database operations. The core technical flaw is essentially an improper neutralization of special elements used in an object-oriented programming context, which aligns with CWE-470: Use of Externally-Controlled Input to Select Classes or Code. By leveraging this reflection mechanism, the application logic is subverted, allowing external actors to dictate internal behavior rather than merely supplying data values.
The operational impact of this vulnerability is severe and multifaceted. Primarily, it can lead to the unintended removal of stored records from the MongoDB database. Because the malicious input triggers methods that alter the document structure or delete associated embedded documents, critical business data can be permanently lost without any audit trail indicating a deliberate deletion action by an authorized user. Furthermore, the vulnerability can cause the embedding application to become unresponsive. This denial-of-service condition arises because the execution of unintended internal methods may trigger infinite loops, resource exhaustion, or exceptions that halt the request processing pipeline. For applications relying on high availability and data integrity, such as financial services platforms or content management systems using Mongoid, this represents a significant risk to both confidentiality through potential information leakage via error states and availability due to service disruption.
This vulnerability is also relevant to broader security frameworks beyond just code quality metrics. In the context of the MITRE ATT&CK framework, this behavior can be categorized under techniques involving command injection or exploitation of software vulnerabilities for impact on system integrity and availability. Specifically, it relates to T1496: Resource Hijacking if the unresponsiveness leads to resource exhaustion, or more broadly to initial access vectors where an attacker might use such a flaw as part of a larger attack chain to escalate privileges or pivot within a networked environment by destabilizing critical backend services. The lack of authentication requirement for this specific vector makes it particularly dangerous in web applications that expose API endpoints directly to end-users without sufficient input sanitization layers between the HTTP request and the ODM layer.
Mitigation strategies must focus on strict input validation and limiting the scope of data accepted by Mongoid's persistence methods. Developers should avoid passing raw user parameters directly into update operations; instead, they should use whitelisting techniques to ensure that only predefined model attributes are updated. Utilizing strong parameter patterns in Ruby frameworks like Rails can help filter out unexpected keys before they reach the ODM layer. Additionally, upgrading to versions of Mongoid where this reflection weakness has been patched is essential if available for the specific version in use. Security teams should also implement comprehensive logging and monitoring to detect anomalous database operations that do not correspond to standard application workflows, which could indicate an active exploitation attempt. Regular security audits focusing on object-document mapping configurations will further reduce the risk of similar vulnerabilities arising from improper handling of dynamic inputs.