CVE-2021-20331 is a medium-severity (CVSS 4.9) Information Exposure vulnerability in mongodb.driver. A fix is available for mongodb.driver — see the affected versions and patch details below.
MongoDB C# Driver Risk of Exposing Authentication Data via Command Listener
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2021-20331.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
mongodb.driverReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.
Description
Specific versions of the MongoDB C# Driver may erroneously publish events containing authentication-related data to a command listener configured by an application. The published events may contain security-sensitive data when commands such as "saslStart", "saslContinue", "isMaster", "createUser", and "updateUser" are executed. Without due care, an application may inadvertently expose this authenticated-related information, e.g., by writing it to a log file. This issue only arises if an application enables the command listener feature (this is not enabled by default). This issue affects the MongoDB C# Driver v2.12 versions prior to and including 2.12.1.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | mongodb.driver | ≥ 2.11.0&&< 2.12.2 | 2.12.2dotnet add package mongodb.driver --version 2.12.2 |
Affected Products
c\# drivermongodbDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mongodb.driver, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update mongodb.driver to 2.12.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-20331 is resolved across your whole dependency graph.
Workarounds
Assume what was exposed is already known: rotate any credential, token or key that the affected component could return, restrict the endpoint to callers that genuinely need it, and strip sensitive fields from responses and error output at the boundary rather than relying on the client not to read them.
Frequently Asked Questions
Is CVE-2021-20331 in your dependencies?
Find it across NuGet, including transitive dependencies.