CVE-2026-9742 Overview
CVE-2026-9742 is a pre-authentication denial-of-service vulnerability affecting MongoDB server deployments configured with OpenID Connect (OIDC) authentication. Unauthenticated clients can send the authenticate command with specific crafted values in the mechanism parameter, causing the server process to crash. The flaw is tracked under CWE-1287: Improper Validation of Specified Type of Input and is documented in MongoDB JIRA Issue SERVER-124183. Because the authenticate command is reachable before authentication completes, any network-adjacent attacker can trigger the crash without credentials.
Critical Impact
Remote unauthenticated attackers can crash MongoDB instances that have OIDC authentication enabled, breaking database availability for all dependent applications.
Affected Products
- MongoDB Server deployments with OIDC authentication enabled in configuration
- Applications and services that rely on affected MongoDB instances for data persistence
- Clustered MongoDB topologies where the authenticate command path is exposed to clients
Discovery Timeline
- 2026-06-09 - CVE-2026-9742 published to NVD
- 2026-06-10 - Last updated in NVD database
Technical Details for CVE-2026-9742
Vulnerability Analysis
The vulnerability resides in the handling of the mechanism parameter inside the MongoDB authenticate command when OIDC authentication is configured. The server fails to properly validate the type or contents of values supplied for mechanism, and certain inputs drive the server into an unrecoverable state that terminates the process. The authenticate command is exposed to unauthenticated clients by design, so exploitation requires no prior access, credentials, or user interaction. A single crafted command produces a full crash of the affected mongod process, denying service to all connected clients and consumers.
Root Cause
The root cause is improper validation of the input type accepted for the mechanism field [CWE-1287]. When OIDC is enabled, the authentication dispatch code path accepts values that it cannot safely process, leading to a fatal error during command handling. Input validation does not constrain the parameter to the expected set of mechanism identifiers before downstream logic attempts to act on it.
Attack Vector
An attacker connects to an exposed MongoDB endpoint over the network and issues a single authenticate command containing a crafted mechanism value. No credentials are required because the command itself is the authentication entry point. The MongoDB process terminates, producing a denial-of-service condition. Replaying the request after restart sustains the outage. Technical details are tracked in MongoDB JIRA Issue SERVER-124183.
Detection Methods for CVE-2026-9742
Indicators of Compromise
- Repeated unexpected terminations of mongod processes shortly after receiving client connections
- authenticate command entries in MongoDB audit or diagnostic logs immediately preceding crash events
- Connection attempts from unfamiliar source IPs targeting MongoDB ports (default 27017) without successful authentication
Detection Strategies
- Monitor MongoDB diagnostic logs for fatal assertions or signal-based shutdowns correlated with inbound authenticate traffic
- Inspect packet captures or proxy logs for authenticate commands carrying unusual mechanism values that do not match supported OIDC mechanism names
- Alert on abnormal restart frequency of mongod services managed by systemd, Kubernetes, or replica set orchestration
Monitoring Recommendations
- Enable MongoDB audit logging for authentication events and forward records to a centralized analytics platform
- Track replica set primary step-downs and unplanned elections, which can indicate repeated crashes of cluster members
- Baseline expected authentication mechanisms in use and alert on deviations to unexpected mechanism strings
How to Mitigate CVE-2026-9742
Immediate Actions Required
- Identify all MongoDB deployments with OIDC authentication enabled and prioritize them for patching
- Restrict network exposure of MongoDB ports to trusted client subnets using firewall rules or security groups
- Apply the vendor fix referenced in MongoDB JIRA Issue SERVER-124183 once the corresponding server release is deployed
Patch Information
MongoDB tracks the fix under SERVER-124183. Operators should upgrade to the MongoDB server release that includes the validation fix for the mechanism parameter in the authenticate command. Consult the MongoDB release notes for the exact fixed versions corresponding to each supported major branch.
Workarounds
- Disable OIDC authentication in the MongoDB configuration until the fixed version is deployed, falling back to alternative supported authentication mechanisms
- Place MongoDB behind a network proxy or service mesh that filters or rate-limits authenticate commands with non-standard mechanism values
- Limit accepted client source addresses through bindIp, firewalls, or private network segmentation to reduce pre-auth exposure
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
