CVE-2026-82060 in MongoDB
Summary
by MITRE • 09/08/2026
In MongoDB, insufficient validation of shard key values during document insertion allowed authenticated users to store documents with specially crafted, operator-shaped objects as shard key values in sharded collections. When change stream events for such documents were processed with the updateLookup full document mode, the crafted values were embedded into internal post-image lookup queries without proper sanitization, causing them to be interpreted as query operators rather than literal equality values. This could result in change stream consumers receiving incorrect post-image documents or encountering non-resumable fatal errors.
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Analysis
by VulDB Data Team • 09/08/2026
The vulnerability described involves a critical flaw in MongoDB's handling of shard key validation within sharded cluster environments, specifically affecting authenticated users who possess the ability to insert documents into collections that utilize range-based sharding strategies. The core technical issue stems from insufficient sanitization and type checking during the document insertion phase for shard keys. While standard field values are typically validated against expected data types such as strings or integers, this flaw allows an attacker to inject specially crafted BSON objects containing query operators directly into the shard key fields of a collection. This bypasses normal validation logic because the system fails to distinguish between literal data intended for storage and structural elements that modify database query behavior when those values are later processed by internal mechanisms.
The operational impact becomes most severe during the processing of change stream events, particularly when configured with the updateLookup full document mode. In this configuration, MongoDB generates post-image documents that represent the state of a record after an update operation to provide consumers with comprehensive context about changes. When the system processes these updates for documents containing the maliciously crafted shard keys, it embeds the unsanitized operator-shaped objects into internal lookup queries used to retrieve or verify document states. Because these embedded values are not properly escaped or converted back to their literal representations, they are interpreted by the query engine as active MongoDB query operators rather than static data fields. This misinterpretation fundamentally alters how the database processes the post-image generation logic for that specific record.
This architectural flaw leads to two primary negative outcomes for change stream consumers and system stability. First, it can result in the delivery of incorrect or corrupted post-image documents to downstream applications relying on these streams for real-time data synchronization or auditing purposes. Applications expecting consistent schema structures may fail to parse the response correctly if unexpected operator objects appear where simple values were anticipated. Second, and more critically, this condition triggers non-resumable fatal errors within the change stream pipeline. These errors disrupt the continuity of event processing, forcing consumers to restart their cursors from scratch or potentially losing data events entirely depending on how the client library handles such interruptions. This degradation in reliability undermines the integrity guarantees that change streams are designed to provide for critical business processes.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation and CWE-74 Injection: Incorrect Escape of Special Elements. The failure lies in the application's inability to properly validate input data (the shard key) before using it in subsequent operations that interpret its structure as code or query logic. In terms of MITRE ATT&CK, this behavior relates to techniques involving Command Injection or Data Manipulation via injection flaws, although here the exploitation is limited by authentication requirements and specific configuration states like updateLookup mode. The attack vector requires an authenticated user with write access to a sharded collection, which limits the scope but does not eliminate the risk for internal threats or compromised service accounts.
Mitigation strategies must focus on both immediate remediation and long-term architectural hardening. Administrators should apply vendor-provided patches that enforce strict type checking and sanitization of shard key values during insertion, ensuring that only primitive data types are accepted as valid shard keys rather than complex BSON objects containing operators. Additionally, organizations relying heavily on change streams for critical operations should evaluate whether the updateLookup full document mode is strictly necessary; if not, switching to a less resource-intensive or safer event format can reduce exposure to this specific code path. Regular auditing of sharded collection schemas and monitoring for anomalous changes in shard key distributions can also help detect potential exploitation attempts early before they cause significant disruption to data pipelines.