CVE-2026-13055 in MongoDB
Summary
by MITRE • 07/22/2026
The `$_internalIndexKey` aggregation expression can be used by any authenticated user to crash a MongoDB server (mongod). The expression fails to handle compound wildcard index specifications, triggering an internal consistency check that aborts the server process. The user must be able to run an aggregation pipeline.
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Analysis
by VulDB Data Team • 07/22/2026
This vulnerability represents a critical denial-of-service condition in MongoDB database systems where authenticated users can trigger a server crash through manipulation of the $_internalIndexKey aggregation expression. The flaw specifically manifests when processing compound wildcard index specifications, causing an internal consistency check to fail and subsequently abort the mongod process. The vulnerability requires no special privileges beyond authentication to exploit, making it particularly dangerous as any authenticated user with aggregation pipeline execution capabilities can potentially disrupt database services.
The technical root cause lies in MongoDB's insufficient input validation within the $_internalIndexKey expression handling mechanism. When the system encounters compound wildcard index specifications, the internal consistency check fails to properly validate or handle these complex index structures, leading to an abrupt process termination. This behavior aligns with CWE-248, representing an unchecked exception that results in abnormal program termination. The vulnerability demonstrates a classic lack of proper error handling in database query processing systems where edge cases are not adequately considered during the implementation phase.
The operational impact of this vulnerability extends beyond simple service disruption as it can affect database availability and potentially compromise data integrity in environments where MongoDB serves critical business functions. Attackers can repeatedly exploit this vulnerability to cause persistent service interruptions, leading to cascading failures in applications dependent on the database. The crash occurs at the server process level rather than just individual query execution, meaning that even a single malicious aggregation pipeline can bring down an entire database instance. This makes the vulnerability particularly attractive to attackers seeking to disrupt operations without requiring elevated privileges or complex exploitation techniques.
Security professionals should implement immediate mitigations including restricting aggregation pipeline access to only trusted users, monitoring for unusual aggregation patterns that might indicate exploitation attempts, and applying vendor-provided patches as soon as they become available. Organizations using MongoDB should also consider implementing network-level controls to limit access to database servers and establish robust monitoring protocols for detecting abnormal server termination events. The vulnerability highlights the importance of thorough edge case testing in database query processing systems and demonstrates how seemingly minor implementation flaws can result in major operational disruptions. This issue relates to ATT&CK technique T1499.004 which involves network denial of service attacks through resource exhaustion or process termination, emphasizing the need for robust error handling mechanisms in database server implementations.