CVE-2026-82058 in Server
Summary
by MITRE • 09/08/2026
A flaw in MongoDB's JSON Schema validation error generation code allows an authenticated user with readWrite privileges to crash the mongod server. When a BSON document containing an array with a malformed numeric field name fails a $jsonSchema items type constraint, the error generation path performs unsafe numeric conversion on the user-controlled field name without proper exception handling, resulting in an uncaught exception that terminates the server process. This is possible because incoming wire protocol BSON validation does not enforce that array element field names are valid, in-range numeric indices.
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Analysis
by VulDB Data Team • 09/08/2026
The vulnerability described constitutes a critical denial of service condition within MongoDB's JSON Schema validation subsystem, specifically affecting versions where this code path remains unpatched. The root cause lies in the handling of BSON documents during schema enforcement operations. When an authenticated user possessing readWrite privileges submits a document that violates a $jsonSchema items type constraint, the server attempts to generate a descriptive error message detailing which field caused the validation failure. In cases involving arrays with malformed numeric field names, this process triggers unsafe numeric conversion logic on user-controlled input without adequate exception handling mechanisms in place.
From a technical perspective, BSON documents representing arrays typically use integer indices as keys for their elements. However, MongoDB's incoming wire protocol does not strictly enforce that these array element field names are valid, in-range numeric indices before they reach the schema validation layer. This design choice allows an attacker to craft a malicious payload containing an array with non-standard or malformed string representations of numbers as keys. When the server processes this document against a JSON Schema definition requiring specific item types, it attempts to parse these malformed field names into integers for error reporting purposes. The conversion routine fails to handle edge cases where the input is not a valid integer representation, leading to an uncaught exception that crashes the mongod process immediately.
The operational impact of this vulnerability is severe due to its potential for remote denial of service attacks against database availability. Since authentication and readWrite privileges are required, the threat model assumes a compromised application server or insider threat scenario where an attacker has legitimate access but limited permissions. Despite these restrictions, the ability to crash the entire mongod instance disrupts all services relying on that database node, leading to significant downtime and potential data inconsistency if replication is not properly configured with automatic failover capabilities. This flaw effectively neutralizes the availability aspect of the CIA triad for any system dependent on this MongoDB deployment.
In terms of industry standard classifications, this vulnerability aligns with CWE-20 Improper Input Validation regarding the failure to validate array element field names during wire protocol ingestion and CWE-754: Improper Check for Unusual or Exceptional Conditions within the error generation logic itself. The exploitation technique maps directly to MITRE ATT&CK T1499 Endpoint Denial of Service, specifically under sub-techniques involving resource exhaustion through application crashes rather than traditional CPU or memory flooding methods. This highlights a shift in attack vectors where simple logical flaws can achieve high-impact availability disruption without requiring complex payload construction or privilege escalation beyond basic write access.
Mitigation strategies must focus on both immediate remediation and long-term architectural improvements. The primary defense is to apply the vendor-provided security patch that addresses this specific code path, ensuring that numeric conversion operations are wrapped in proper try-catch blocks or validated using safe parsing functions before being used in error messages. Additionally, administrators should enforce strict input validation at the application layer to prevent malformed BSON structures from reaching the database engine whenever possible. Implementing network-level access controls and restricting readWrite privileges to only essential service accounts can further reduce the attack surface by limiting the number of entities capable of triggering this flaw. Regular auditing of schema definitions and monitoring for unusual error logs related to JSON Schema validation failures will also aid in early detection of exploitation attempts or misconfigurations that might expose similar vulnerabilities.