CVE-2026-82056 in MongoDB
Summary
by MITRE • 09/08/2026
A race condition in MongoDB server's text index query parsing can cause a heap use-after-free read when handling upsert retry paths. Under certain concurrent index lifecycle operations, a raw pointer to internal text index metadata may be dereferenced after the underlying structures have been freed, leading to a server crash. An authenticated user with readWrite privileges can trigger this condition through specific concurrent text-search and index management operations, resulting in denial of service for all connected clients. This
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Analysis
by VulDB Data Team • 09/08/2026
The vulnerability identified involves a critical race condition within the MongoDB server's handling of text index query parsing, specifically during upsert retry paths. This flaw manifests as a heap use-after-free read, where a raw pointer to internal text index metadata is dereferenced after the underlying memory structures have already been deallocated by concurrent operations. The root cause lies in the complex interaction between the database engine's concurrency control mechanisms and its dynamic indexing subsystems. When multiple threads operate simultaneously on text indexes, particularly during lifecycle changes such as creation or dropping while queries are being executed, the synchronization primitives fail to maintain consistent state references across all execution paths. This lack of proper atomicity allows a thread to retain a reference to memory that has been freed by another thread managing index metadata, leading to undefined behavior and ultimately a server crash when that stale pointer is accessed.
From an operational perspective, this vulnerability poses a severe risk to the availability of MongoDB instances running vulnerable versions. The impact is characterized as a denial of service for all connected clients because the process termination caused by the segmentation fault or memory corruption halts database operations entirely. An authenticated user possessing readWrite privileges can exploit this condition by orchestrating specific concurrent text-search queries alongside index management operations, such as creating or dropping text indexes on collections involved in those searches. The attacker does not need to execute arbitrary code but simply needs to trigger the race condition through legitimate administrative actions combined with high-concurrency query patterns. This makes detection and prevention challenging for administrators who may not anticipate that standard maintenance tasks could destabilize the server under load.
In terms of industry standards, this vulnerability aligns closely with CWE-416, Use After Free, which describes situations where a program continues to use a pointer after it has been freed, often leading to crashes or potential code execution if controlled data is written before reallocation. Additionally, the exploitation vector relates to ATT&CK technique T1529, System Shutdown/Reboot, as the successful exploitation results in service unavailability through process termination. While typically classified under availability impacts rather than confidentiality or integrity breaches due to the read-only nature of the initial dereference, the instability introduced can have cascading effects on data consistency if transactions are interrupted mid-flight during a crash recovery scenario.
Mitigation strategies primarily involve upgrading to patched versions of MongoDB where the race condition has been resolved through improved synchronization mechanisms and safer pointer management practices within the text index subsystem. Administrators should also consider implementing operational mitigations such as limiting concurrent access patterns that mix heavy read-write workloads with schema changes on collections utilizing text indexes. Monitoring for high rates of index creation or deletion during peak query times can help identify potential trigger conditions before they result in a crash. Furthermore, ensuring that database processes are monitored by robust restart services like systemd or supervisord can minimize downtime by automatically recovering the service after an unexpected termination, although this does not prevent data loss from interrupted transactions.