CVE-2026-89099: MongoDB Server Race Condition Vulnerability

CVE-2026-89099 Overview

CVE-2026-89099 is a race condition in the document value layer of MongoDB Server. Concurrent server threads can operate on the same internal memory without synchronization, resulting in memory corruption. An authenticated user with ordinary read-write privileges on a database can trigger the condition over the standard client protocol. Successful exploitation terminates the server process and can corrupt process memory with attacker-influenced content. The vulnerability affects the confidentiality, integrity, and availability of the affected MongoDB Server process. The issue is tracked under CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization and is documented in MongoDB Jira Issue SERVER-134063.

Critical Impact
Any authenticated database user with read-write access can crash the MongoDB Server process and potentially influence corrupted memory contents, impacting service availability and data integrity.

Affected Products

MongoDB Server (specific version ranges tracked in SERVER-134063)
Deployments exposing the client wire protocol to authenticated users
Environments where standard read-write roles are granted to application or third-party accounts

Discovery Timeline

2026-09-11 - CVE-2026-89099 published to the National Vulnerability Database
2026-09-18 - Last updated in NVD database

Technical Details for CVE-2026-89099

Vulnerability Analysis

The flaw resides in the document value layer of MongoDB Server, the internal component responsible for representing and manipulating BSON document values in memory. Multiple server threads can access shared value structures concurrently without appropriate synchronization primitives. When two threads interleave operations on the same allocation, the state of that memory becomes undefined. The result is memory corruption that can crash the server process. Because the corrupted region may contain content derived from user-supplied input, the fault can be reached and shaped through the ordinary client wire protocol rather than through administrative interfaces.

Root Cause

The root cause is a missing or insufficient synchronization boundary around shared document value memory [CWE-362]. Server threads read and mutate the same internal buffers without holding a lock, atomic guard, or equivalent ordering primitive. Under concurrent workloads that exercise the same document values, this produces a data race that manifests as memory corruption and process termination.

Attack Vector

Exploitation requires network access to the MongoDB client protocol and authenticated credentials with ordinary read-write privileges on at least one database. No administrative role, elevated permission, or user interaction is required. An attacker issues concurrent operations crafted to interleave against the vulnerable value layer. A successful race terminates the mongod process, producing a denial-of-service condition and, in some cases, corrupted process memory reflecting attacker-controlled data. See MongoDB Jira Issue SERVER-134063 for vendor tracking details.

No public proof-of-concept code is available at this time. The EPSS score for CVE-2026-89099 is 0.182%.

Detection Methods for CVE-2026-89099

Indicators of Compromise

Unexpected mongod process crashes or restarts, particularly under multi-client concurrent workloads
Core dumps or fatal assertion messages in MongoDB logs referencing document value or BSON handling paths
Repeated authenticated sessions from a single client issuing high-concurrency operations against the same documents
Sudden replica set primary step-downs or secondary resyncs caused by primary termination

Detection Strategies

Monitor MongoDB server logs for F (fatal) severity entries, invariant failures, and stack traces originating in value or BSON code paths.
Alert on abnormal restart counts for mongod processes across the cluster within short time windows.
Correlate authentication events with process termination timestamps to identify the originating client credential.
Track query and command rates per authenticated principal to surface anomalous concurrent write patterns against shared documents.

Monitoring Recommendations

Enable MongoDB audit logging to capture authenticated operations and the roles used to execute them.
Forward mongod logs and process supervisor events to a centralized logging or SIEM platform for retention and correlation.
Baseline normal client concurrency levels so that deviations from application patterns can be flagged.
Monitor replica set health metrics for unplanned elections that correlate with server crashes.

How to Mitigate CVE-2026-89099

Immediate Actions Required

Inventory all MongoDB Server deployments and identify instances exposed to authenticated users with read-write roles.
Apply the fixed MongoDB Server release referenced in SERVER-134063 as soon as it is available for your deployment channel.
Audit database role assignments and revoke read-write privileges from accounts that only require read access.
Restrict network reachability of mongod to trusted application tiers using firewall rules or private networking.

Patch Information

Refer to the MongoDB Jira Issue SERVER-134063 for the authoritative list of fixed versions and backport branches. Upgrade all replica set members and sharded cluster components to a patched build. Rolling upgrades should follow MongoDB's documented procedure to preserve availability during remediation.

Workarounds

Enforce least-privilege role assignments so that only trusted service accounts hold read-write privileges on production databases.
Terminate mongod client connections from untrusted networks using network segmentation and IP allowlists.
Rate-limit or throttle concurrent write operations per authenticated principal at the application or proxy layer where feasible.
Increase monitoring sensitivity on mongod availability so that exploitation attempts are detected and contained quickly.

bash

# Example: restrict a MongoDB user to read-only access on a database
mongosh --eval 'db.getSiblingDB("admin").updateUser("app_user", { roles: [ { role: "read", db: "appdb" } ] })'

# Example: bind mongod to a private interface and require authentication
# /etc/mongod.conf
# net:
#   bindIp: 127.0.0.1,10.0.0.10
# security:
#   authorization: enabled