CVE-2026-104004 in Server
Summary
by MITRE • 10/13/2026
MongoDB Server's collection validation feature may not properly handle certain expressions stored in a validator. In some cases, this can cause the server process to stop running when a document is later inserted. The behavior can occur for authenticated users with write access.
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Analysis
by VulDB Data Team • 10/13/2026
The vulnerability identified within MongoDB Server pertains specifically to its collection validation mechanism, which serves as a critical control for enforcing data integrity and schema compliance at the database level. This feature allows administrators to define JSON Schema validators that restrict the structure, type, or content of documents inserted into a collection. The core technical flaw lies in the improper handling of specific expressions embedded within these validator definitions. When a document is subsequently inserted into a validated collection, the server attempts to evaluate the stored expression against the incoming data. Due to insufficient validation or error handling logic during this evaluation phase, certain malformed or edge-case expressions can trigger an unhandled exception within the database engine. This internal failure results in the termination of the MongoDB server process, effectively causing a denial of service for all clients connected to that instance.
From a technical perspective, this issue represents a classic case of improper input validation leading to application crash, which aligns with CWE-20 Improper Input Validation and potentially CWE-400 Resource Exhaustion if the repeated crashes lead to system instability. The vulnerability is particularly severe because it can be exploited by authenticated users who possess write access to the affected collection. This means that an attacker does not need administrative privileges or full server control; rather, standard application-level credentials are sufficient to trigger the crash. By crafting a document with specific fields that match the problematic validator expression pattern, an adversary can force the database engine into a fatal error state. The operational impact is immediate and significant, as the cessation of the MongoDB process disrupts all read and write operations for any service relying on that instance, leading to potential data loss if transactions are in progress or extended downtime while the service is restarted and recovered.
This behavior also maps directly to MITRE ATT&CK technique T1499 Endpoint Denial of Service, specifically under sub-techniques involving application exhaustion or resource consumption through crash-inducing inputs. The ability for a lower-privileged user to impact the availability of the entire database server highlights a critical gap in privilege separation and fault isolation within the validation subsystem. In production environments where high availability is paramount, such vulnerabilities can be leveraged by malicious insiders or compromised applications to disrupt business continuity without needing to exfiltrate sensitive data. The severity is further compounded if the MongoDB instance is exposed directly to untrusted networks, although authentication requirements typically limit this attack surface to internal network threats or authenticated API consumers.
Mitigation strategies must focus on both immediate remediation and long-term architectural improvements. The primary solution involves upgrading to a patched version of MongoDB Server where the validation engine has been hardened against these specific expression patterns. Database administrators should also review existing collection validators for complex or custom expressions, ensuring they adhere strictly to supported JSON Schema specifications without relying on edge-case behaviors that might trigger parser errors. Implementing robust monitoring and alerting systems is essential to detect unexpected process restarts quickly, allowing for rapid incident response. Furthermore, applying the principle of least privilege ensures that only trusted applications have write access to collections with strict validation rules, reducing the attack surface available to potential adversaries. Regular security audits of database configurations and validator schemas can help identify similar risky patterns before they are exploited in live environments.