CVE-2026-82059 in Server
Summary
by MITRE • 09/08/2026
An internal aggregation expression in MongoDB Server was incorrectly registered as accessible to any authenticated user rather than being restricted to internal cluster operations. By crafting a malformed index specification within this expression, an authenticated user with read-only privileges could trigger an assertion failure in the index key generation code path. In certain build configurations, this assertion failure results in termination of the mongod process, causing a denial of service to all connected clients.
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Analysis
by VulDB Data Team • 09/08/2026
The vulnerability described involves a critical misconfiguration within MongoDB Server's internal aggregation expression framework, specifically concerning access control and privilege escalation boundaries. The core issue stems from an incorrect registration of certain internal expressions that were inadvertently exposed as accessible to any authenticated user rather than being strictly reserved for internal cluster operations. This architectural flaw creates a significant gap in the expected security model where administrative or read-only users are assumed to have limited interaction with low-level system components. By exploiting this misconfiguration, an attacker who possesses even minimal authentication credentials can invoke these restricted functions, effectively bypassing intended privilege restrictions and gaining access to code paths that should remain isolated from standard user interactions.
The technical exploitation of this flaw relies on the manipulation of index specifications within the affected aggregation expression. When a malicious actor crafts a malformed or specifically designed index specification payload, it triggers an assertion failure deep within the MongoDB server's index key generation logic. Assertions in software development are typically used to catch programming errors and invalid states during execution; however, when these assertions fail due to external input rather than internal bugs, they often lead to unhandled exceptions or forced process termination depending on the build configuration of the database instance. In this specific scenario, the malformed index specification causes the server's assertion mechanism to activate, leading directly to the abrupt termination of the mongod process. This behavior transforms what might otherwise be a simple error response into a severe stability issue for the entire database service.
The operational impact of this vulnerability is primarily characterized by a denial of service condition affecting all connected clients and applications relying on the MongoDB instance. Because the exploitation results in the termination of the main server process, any active connections are immediately dropped, and ongoing transactions are aborted without proper cleanup or rollback mechanisms visible to the client layer. This leads to significant downtime for services dependent on real-time data access from that specific node. In environments utilizing replica sets or sharded clusters, while high availability features might mitigate total service loss by promoting a secondary member, the immediate effect remains a disruption of write and read operations until failover completes. Furthermore, repeated exploitation attempts could lead to resource exhaustion if not properly rate-limited, exacerbating the denial of service impact across the infrastructure.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation, as the server fails to adequately sanitize or validate the structure and content of index specifications provided by authenticated users before processing them in critical code paths. Additionally, it relates to CWE-787 Out-of-bounds Write if the assertion failure stems from memory corruption issues triggered by the malformed data, although the primary manifestation here is process termination via assertion logic. In terms of attack vectors, this falls under MITRE ATT&CK technique T1499 Endpoint Denial of Service, specifically involving resource exhaustion or service disruption through application-level exploits rather than network flooding. The vulnerability also touches upon CWE-269 Improper Privilege Management due to the incorrect exposure of internal-only functions to lower-privileged users.
Mitigation strategies for this issue require immediate attention from database administrators and security teams responsible for MongoDB deployments. The primary remediation is to apply vendor-provided patches or upgrade to a version where the access control logic for aggregation expressions has been corrected to properly restrict these operations to internal cluster contexts only. Until patching can be performed, organizations should implement strict network-level controls such as firewall rules to limit direct database port exposure and ensure that all MongoDB instances are protected by strong authentication mechanisms with minimal privilege assignments. Additionally, enabling comprehensive logging and monitoring for assertion failures or abnormal process restarts can help in early detection of exploitation attempts. It is also advisable to review application code interacting with the database to ensure that index creation operations use validated schemas and do not pass untrusted input directly into aggregation pipelines without rigorous validation layers at the application level.