CVE-2026-18693 in MongoDB
Summary
by MITRE • 08/11/2026
An issue in MongoDB Server's handling of timeseries collections could allow an authenticated user with write privileges to cause an internal data structure to become inconsistent through certain document insertions. A subsequent insert into the affected bucket could then result in the server accessing memory outside its intended bounds, potentially causing a server crash (denial of service), exposure of limited memory contents, or memory corruption.
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Analysis
by VulDB Data Team • 08/11/2026
This vulnerability exists within MongoDB Server's implementation of timeseries collections, representing a critical data integrity flaw that can be exploited through authenticated write operations. The issue stems from inadequate validation during document insertion processes where specific sequence of writes can corrupt internal data structures. When an authenticated user with appropriate write privileges performs certain document insertions, the server's timeseries bucket management logic fails to properly maintain consistency between its internal metadata and actual data storage structures. This inconsistency becomes particularly dangerous when subsequent insertions target the same affected bucket, as it triggers memory access violations that can lead to unpredictable behavior.
The technical flaw manifests as a buffer overread condition within MongoDB's timeseries collection handling code, where the server attempts to access memory locations beyond its allocated boundaries during document processing operations. This type of vulnerability falls under CWE-125: Uncontrolled Buffer Access and aligns with ATT&CK technique T1499.004: Endpoint Denial of Service, specifically targeting service availability through memory corruption. The root cause appears to be insufficient bounds checking in the timeseries bucket management subsystem, particularly when handling document insertion sequences that modify existing data structures.
The operational impact of this vulnerability extends beyond simple denial of service scenarios to potentially expose sensitive memory contents and cause persistent system instability. When the server experiences a memory access violation during subsequent insertions, it may crash and restart automatically, leading to extended downtime for applications relying on MongoDB timeseries functionality. Additionally, the memory corruption could potentially expose confidential data stored in adjacent memory regions, though the extent of information disclosure would depend on the specific memory layout at the time of the overflow. This vulnerability affects MongoDB deployments using timeseries collections, particularly those with high write throughput scenarios where multiple concurrent insertions might trigger the condition.
Organizations should immediately implement mitigations including applying the latest MongoDB security patches that address this specific buffer overread issue in timeseries collection handling. Access controls should be strictly enforced to limit write privileges to only trusted users and applications, while monitoring systems should be deployed to detect unusual insertion patterns that might indicate exploitation attempts. Network segmentation can help limit the attack surface by restricting direct access to MongoDB instances from untrusted networks. Database administrators should also consider implementing regular backups and establishing incident response procedures specifically for handling memory corruption events. The vulnerability demonstrates the importance of thorough testing for edge cases in time-series data management systems, particularly when dealing with concurrent write operations that modify shared internal data structures. Organizations using MongoDB timeseries collections should conduct immediate security assessments to identify potentially affected deployments and prioritize patching efforts based on their risk exposure levels.