CVE-2020-13927: Apache Airflow Auth Bypass Vulnerability

CVE-2020-13927 Overview

CVE-2020-13927 is a critical authentication bypass vulnerability in Apache Airflow's Experimental API. The previous default configuration allowed all API requests without authentication, exposing systems to unauthenticated remote access. This insecure default poses significant security risks to users who overlook this configuration detail, potentially allowing attackers to execute arbitrary code on vulnerable Airflow instances.

Critical Impact

This vulnerability allows unauthenticated remote attackers to access the Airflow Experimental API and potentially execute arbitrary code on affected systems. CISA has added this CVE to the Known Exploited Vulnerabilities catalog.

Affected Products

• Apache Airflow versions prior to 1.10.11
• Apache Airflow installations with default API authentication settings
• Existing Airflow deployments that have not updated their configuration after upgrading

Discovery Timeline

• 2020-11-10 - CVE-2020-13927 published to NVD
• 2025-10-23 - Last updated in NVD database

Technical Details for CVE-2020-13927

Vulnerability Analysis

This vulnerability stems from an insecure default configuration in Apache Airflow's Experimental API (CWE-306: Missing Authentication for Critical Function). Prior to version 1.10.11, the default setting for the [api]auth_backend configuration parameter was set to allow all API requests without any authentication mechanism. This design flaw creates a significant attack surface where remote unauthenticated attackers can interact with the Airflow API endpoints freely.

The vulnerability is particularly dangerous because it affects a workflow orchestration platform commonly used in data engineering and ETL pipelines. Successful exploitation can lead to complete system compromise, data exfiltration, and lateral movement within enterprise networks. Public exploits are available demonstrating remote code execution capabilities against vulnerable installations.

Root Cause

The root cause is an insecure default configuration where the Experimental API was configured to accept all requests without authentication. The [api]auth_backend setting defaulted to allowing unauthenticated access rather than implementing a secure-by-default approach. This configuration oversight was addressed in Airflow 1.10.11 by changing the default to airflow.api.auth.backend.deny_all, which denies all requests by default.

Attack Vector

The attack vector is network-based, requiring no authentication, no user interaction, and low complexity to exploit. Attackers can send unauthenticated HTTP requests to the Airflow Experimental API endpoints over the network. Once access is gained to the API, attackers can leverage various endpoints to trigger DAGs (Directed Acyclic Graphs), access sensitive configuration information, and ultimately achieve remote code execution on the underlying system.

The vulnerability has been documented in multiple public exploits available on Packet Storm Security, demonstrating the practical exploitability of this authentication bypass leading to remote code execution.

Detection Methods for CVE-2020-13927

Indicators of Compromise

• Unexpected or unauthorized API requests to Airflow's Experimental API endpoints (typically /api/experimental/*)
• Anomalous DAG trigger events without corresponding legitimate user activity
• Unusual process spawning or command execution originating from the Airflow webserver process
• Network connections to or from the Airflow instance from unknown or suspicious IP addresses

Detection Strategies

• Monitor HTTP access logs for requests to /api/experimental/* endpoints, especially from external or untrusted IP addresses
• Implement network-based intrusion detection rules to identify exploitation attempts targeting Airflow API endpoints
• Review Airflow configuration files to verify [api]auth_backend is set to a secure value
• Deploy web application firewalls (WAF) to detect and block suspicious API access patterns

Monitoring Recommendations

• Enable detailed logging for all Airflow API requests and centralize logs for analysis
• Set up alerts for any API authentication failures or bypasses
• Monitor for unexpected DAG executions or task completions that don't correlate with scheduled workflows
• Implement baseline monitoring for Airflow process behavior to detect anomalous command execution

How to Mitigate CVE-2020-13927

Immediate Actions Required

• Upgrade Apache Airflow to version 1.10.11 or later immediately
• For existing installations, update the configuration to set [api]auth_backend = airflow.api.auth.backend.deny_all or implement proper authentication
• Restrict network access to Airflow instances using firewall rules to limit exposure
• Audit Airflow logs for any signs of unauthorized API access or exploitation

Patch Information

Apache Airflow version 1.10.11 addresses this vulnerability by changing the default API authentication backend to deny all requests. New installations after 1.10.11 are protected by default. However, existing installations upgrading to 1.10.11 must manually update their configuration as the upgrade process does not automatically modify existing configuration files. Refer to the Apache Airflow Updating Guide for detailed migration instructions. Additional security documentation is available at the Airflow Security Documentation.

Workarounds

• Set [api]auth_backend = airflow.api.auth.backend.deny_all in airflow.cfg to disable the Experimental API entirely if not required
• Implement network segmentation to prevent external access to Airflow instances
• Configure a reverse proxy with authentication in front of Airflow to add an additional authentication layer
• Use the stable REST API with proper authentication instead of the Experimental API

# Configuration example
# Update airflow.cfg to secure the Experimental API
# Add or modify the following in your airflow.cfg file:

[api]
auth_backend = airflow.api.auth.backend.deny_all

# Alternatively, implement proper authentication:
# auth_backend = airflow.api.auth.backend.basic_auth

# After updating configuration, restart Airflow services:
# systemctl restart airflow-webserver
# systemctl restart airflow-scheduler