CVE-2026-82064: MongoDB Server DOS Vulnerability

CVE-2026-82064 Overview

CVE-2026-82064 is a denial of service vulnerability in MongoDB Server. An unauthenticated network attacker can crash a specific type of replica set member by triggering a reachable assertion in the read concern processing logic. The assertion holds assumptions about internal state that do not apply to all member configurations, causing the server process to terminate when violated. The flaw is classified as [CWE-617] Reachable Assertion.

Critical Impact
Remote, unauthenticated attackers can terminate MongoDB replica set member processes, disrupting database availability without any credentials or user interaction.

Affected Products

MongoDB Server (replica set deployments)
Specific replica set member configurations exposing read concern processing
Refer to MongoDB JIRA SERVER-130759 for exact affected versions

Discovery Timeline

2026-09-08 - CVE-2026-82064 published to the National Vulnerability Database (NVD)
2026-09-08 - Last updated in NVD database

Technical Details for CVE-2026-82064

Vulnerability Analysis

The vulnerability resides in MongoDB Server's read concern processing logic. The code contains an assertion that validates internal state assumptions before continuing execution. When a client submits a request that reaches this code path on a replica set member whose configuration does not satisfy those assumptions, the assertion fails and the server process terminates.

Because the assertion is reachable prior to authentication, any network-adjacent attacker who can send traffic to the MongoDB port can trigger the crash. The impact is limited to availability. Confidentiality and integrity of stored data are not affected by this issue.

Repeated exploitation forces continuous process restarts, degrading replica set quorum and potentially forcing failover cycles. For deployments with a small number of voting members, sustained crashes can lead to loss of write availability.

Root Cause

The root cause is a reachable assertion [CWE-617] in the read concern handler. The assertion assumes an internal state invariant that is true for typical primary and secondary members but not for all replica set member types. When the invariant does not hold, MongoDB's assertion machinery treats the condition as unrecoverable and terminates the process rather than returning an error to the client.

Attack Vector

An attacker sends a crafted read operation over the network to a vulnerable replica set member. No authentication or user interaction is required. The request traverses the read concern processing path, evaluates the assertion, and forces the mongod process to exit. The MongoDB JIRA tracker SERVER-130759 contains vendor-controlled technical details.

No public proof-of-concept exploit is currently listed for CVE-2026-82064, and the vulnerability is not present on the CISA Known Exploited Vulnerabilities catalog.

Detection Methods for CVE-2026-82064

Indicators of Compromise

Unexpected mongod process termination entries in system logs or systemd journal
MongoDB log entries showing assertion failures within read concern handling code paths
Repeated replica set member state transitions (SECONDARY to STARTUP2, primary step-downs) without operator action
Elevated inbound traffic to MongoDB listener ports (default 27017) from unexpected sources

Detection Strategies

Monitor MongoDB server logs for fatal assertion messages and abnormal shutdown events correlated with recent client activity
Baseline replica set member uptime and alert on short-lived processes or crash loops
Inspect network flows to MongoDB endpoints for unauthenticated sessions that immediately precede process exits
Correlate mongod exit codes with preceding client commands using centralized logging

Monitoring Recommendations

Ingest MongoDB and operating system logs into a centralized SIEM for correlation of crash events with client sources
Configure alerts for replica set health changes, including member state flapping and unplanned failovers
Track process restart counts per host and trigger investigation when thresholds are exceeded
Enforce network-level allowlists so only trusted application hosts can reach MongoDB ports

How to Mitigate CVE-2026-82064

Immediate Actions Required

Review MongoDB JIRA SERVER-130759 to identify fixed versions applicable to your deployment
Restrict network access to MongoDB replica set members using firewall rules or security groups, permitting only authorized application hosts
Enable authentication and TLS on all MongoDB deployments to reduce exposure of the pre-authentication code path
Audit replica set topologies to identify member types that match the vulnerable configuration described in the advisory

Patch Information

Apply the MongoDB Server updates referenced in SERVER-130759. Fixed versions and upgrade guidance are maintained by MongoDB in that tracker. Coordinate rolling upgrades across replica set members to preserve quorum during the patch process.

Workarounds

Place MongoDB behind a network segment that blocks untrusted clients from reaching listener ports
Require authentication (security.authorization: enabled) on all replica set members to shrink the pre-authenticated attack surface where feasible
Increase the number of voting members so that a single crashed member does not eliminate write availability
Deploy connection rate limiting and anomaly detection in front of MongoDB endpoints

bash

# Configuration example: restrict MongoDB exposure and require authentication
# /etc/mongod.conf
net:
  bindIp: 127.0.0.1,10.0.0.10
  port: 27017
  tls:
    mode: requireTLS
    certificateKeyFile: /etc/ssl/mongodb.pem
security:
  authorization: enabled

# Example host firewall rule: allow only the application subnet
iptables -A INPUT -p tcp --dport 27017 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 27017 -j DROP