CVE-2026-82076: MongoDB Server DOS Vulnerability

CVE-2026-82076 is a denial of service vulnerability in MongoDB Server caused by an integer overflow in query planning. Authenticated users can craft queries that exhaust memory and crash the server. This article covers technical details, affected versions, impact analysis, and mitigation strategies.

CVE-2026-82076 Overview

CVE-2026-82076 is an integer overflow vulnerability [CWE-190] in the query planning component of MongoDB Server. An authenticated user holding standard database-level read/write privileges can submit a specially crafted query that bypasses an internal resource limit. The server then consumes memory without bound during query planning, and the resulting exhaustion terminates the mongod process. The impact is a denial of service affecting every database served by the affected node.

Critical Impact
A low-privileged authenticated user can crash a MongoDB node, disrupting availability across all databases hosted on that instance.

Affected Products

MongoDB Server (query planning component)
Deployments where authenticated users hold ordinary database-level read/write privileges
Refer to the MongoDB Jira Issue SERVER-128253 for fixed version details

Discovery Timeline

2026-09-08 - CVE-2026-82076 published to the National Vulnerability Database (NVD)
2026-09-08 - Last updated in NVD database

Technical Details for CVE-2026-82076

Vulnerability Analysis

The flaw resides in MongoDB Server's query planner. During planning, the server evaluates candidate execution plans and enforces internal limits intended to cap memory consumption. An integer overflow in the arithmetic that enforces this cap allows a crafted query to sidestep the limit. The planner then allocates memory without bound while enumerating candidate plans, leading to process termination once system memory is exhausted.

Because mongod serves every database on the node from a single process, termination affects all tenants and databases on the instance. In replica set or sharded deployments, cascading failovers may follow if adjacent nodes receive the same crafted query.

Root Cause

The root cause is an integer overflow [CWE-190] in the resource accounting logic of the query planning subsystem. Arithmetic operations that compute or check a resource ceiling wrap around, producing a value that satisfies the limit check while representing an effectively unbounded allocation budget. The planner proceeds under the incorrect assumption that memory usage remains within policy.

Attack Vector

Exploitation requires network access to the MongoDB endpoint and valid credentials with ordinary read/write privileges on at least one database. No elevated role such as dbAdmin, clusterAdmin, or root is required. The attacker issues a specially crafted query through any supported driver or the mongosh shell. The planner allocates memory until the operating system terminates the process. Refer to the MongoDB Jira Issue SERVER-128253 for technical specifics on the triggering query shape.

Detection Methods for CVE-2026-82076

Indicators of Compromise

Unexpected termination of mongod processes, particularly with out-of-memory (OOM) killer entries in dmesg or /var/log/messages
Sudden spikes in resident set size (RSS) for mongod immediately preceding a crash
Repeated replica set primary elections or shard node restarts without a preceding configuration change
MongoDB log entries showing long-running query planning operations followed by an abrupt shutdown

Detection Strategies

Enable MongoDB audit logging and correlate authenticated query submissions with process termination events
Alert on mongod process restarts and OOM kill events sourced from host telemetry
Baseline query planner latency and memory metrics via serverStatus and flag statistical outliers

Monitoring Recommendations

Ingest MongoDB logs, host process events, and kernel OOM events into a centralized analytics platform
Track per-user query patterns to identify accounts submitting anomalous or repeatedly failing queries
Monitor availability of replica set members and shard primaries for unexplained failovers

How to Mitigate CVE-2026-82076

Immediate Actions Required

Review the MongoDB Jira Issue SERVER-128253 and upgrade MongoDB Server to a fixed release as soon as it is available in your channel
Audit database users and remove read/write privileges that are not required for business function
Restrict network exposure of MongoDB endpoints to trusted application tiers only

Patch Information

MongoDB tracks the fix under Jira issue SERVER-128253. Consult the referenced advisory for the specific patched versions across supported release branches and apply the upgrade during a maintenance window. In replica set deployments, perform rolling upgrades to preserve availability.

Workarounds

Enforce least privilege by removing broad readWrite roles from users that do not require them
Place MongoDB behind a network policy that limits access to trusted application hosts
Configure host-level memory limits and cgroup constraints on mongod to contain the blast radius of a single crash
Enable audit logging to attribute crashing queries to a specific authenticated principal

bash

# Example: restrict MongoDB bind address and enable authentication in mongod.conf
net:
  bindIp: 10.0.0.5,127.0.0.1
  port: 27017
security:
  authorization: enabled
auditLog:
  destination: file
  format: JSON
  path: /var/log/mongodb/audit.json