Apache Airflow: Missing Authentication for Critical Function (CVE-2020-13927)

What is affected, what to do

The previous default setting for Airflow's Experimental API was to allow all API requests without authentication, but this poses security risks to users who miss this fact. From Airflow 1.10.11 the default has been changed to deny all requests by default and is documented at https://airflow.apache.org/docs/1.10.11/security.html#api-authentication.

The vulnerability is being actively exploited; treat it as a priority. Update python/cpython to version 3.6.13, Apache Airflow to version 1.10.13, airflow to version 1.10.15. Immediate actions, mitigation and detection rules are in the runbook below.

Affected

• Apache Airflow eq Apache Airflow <1.10.11..Apache Airflow <1.10.11

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Metrics

Response and mitigation

1. 01

   Runbook step 1

   Immediate response (0-24 h)

   • Inventory every Airflow deployment (pip show apache-airflow, container images, Helm releases) and flag versions < 1.10.11; schedule an upgrade to at least 1.10.11, preferably to a currently supported 2.x line.
   • Immediately set [api] auth_backend = airflow.api.auth.backend.deny_all in airflow.cfg (or airflow.api.auth.backend.basic_auth / Kerberos if the API is actively used) and restart scheduler and webserver. Upgrades of existing installs do NOT migrate this setting automatically.
   • Remove the webserver port (default TCP/8080) from the internet: adjust perimeter firewall, security group or ingress rule so only an admin VLAN or VPN can reach it. UI and Experimental API share the same port.
   • Compromise audit: review all DAGs for unknown tasks, newly added BashOperator/PythonOperator entries and altered dag_run objects; treat Connections, Variables and the Fernet key as potentially exposed and rotate them.
   • Rotate service accounts consumed by Airflow (DB users, cloud IAM keys, SSH keys stored in Connections), since an unauthenticated API call can trigger arbitrary DAGs and exfiltrate those credentials.
2. 02

   Runbook step 2

   Mitigation layers

   • Network segmentation: run the Airflow webserver only behind a reverse proxy (nginx, Traefik) fronted by mTLS or an SSO proxy (OAuth2-Proxy, Keycloak Gatekeeper); direct TCP/8080 access limited to a defined management CIDR.
   • WAF / reverse-proxy rule: outright block path /api/experimental/* while the API is not required. If required, allow only POST /api/experimental/dags/<dag_id>/dag_runs from an allowlisted source IP set and return HTTP 403 otherwise.
   • Configuration hardening: [webserver] expose_config = False, rbac = True, remove the default airflow/airflow admin, regenerate the Fernet key, and explicitly set [api] enable_experimental_api = False on 1.10.x where supported.
   • Container / host hardening: run Airflow workers in a dedicated namespace or network with no egress to production databases beyond what is needed; non-root Pod SecurityContext; read-only root filesystem for webserver containers.
   • IAM least privilege: the Linux service user running the webserver must not have write access to the DAGs folder, so API-triggered code injection cannot be made persistent.
   • Monitoring baseline: pipe Prometheus or StatsD metrics into an alert that fires on sudden spikes of dag_run.created.
3. 03

   Runbook step 3

   Detection rules

   • Reverse-proxy / webserver access logs for GET|POST /api/experimental/ without a preceding /login from the same session: index=web sourcetype=nginx uri_path="/api/experimental/*" | stats count by src_ip, uri_path, status. Any hit from external subnets is already an alert.
   • Sigma shape (process_creation): Airflow worker spawning /bin/sh -c or curl | sh shortly after an Experimental-API call — parent_image ends in airflow or python, child_image in sh|bash|curl|wget|nc. Maps to Sysmon EID 1 or auditd EXECVE.
   • Airflow-native logs ($AIRFLOW_HOME/logs/scheduler/*.log) for unexpected dag_run entries with external_trigger=True and a conf payload containing shell metacharacters — hourly diff against the baseline DAG list.
   • Network telemetry (Zeek http.log / Suricata): HTTP requests to port 8080 with URI pattern */dags/*/dag_runs lacking an Authorization header. Suricata skeleton: alert http any any -> $AIRFLOW_HOST 8080 (msg:"Airflow Experimental API unauth call"; http.uri; content:"/api/experimental/"; http.header; content:!"Authorization"; sid:1000013927;).
   • EDR process ancestry: unusual child processes under the Airflow scheduler, especially reverse-shell indicators (bash -i, python -c 'import socket', powershell -enc) — correlate as high severity with a preceding API hit.

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2

NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

Read in glossary

Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).

CRA

The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

Read in glossary

Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.

ISO/IEC 27001

ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

Read in glossary

Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

Description

The previous default setting for Airflow's Experimental API was to allow all API requests without authentication, but this poses security risks to users who miss this fact. From Airflow 1.10.11 the default has been changed to deny all requests by default and is documented at https://airflow.apache.org/docs/1.10.11/security.html#api-authentication. Note this change fixes it for new installs but existing users need to change their config to default `[api]auth_backend = airflow.api.auth.backend.deny_all` as mentioned in the Updating Guide: https://github.com/apache/airflow/blob/1.10.11/UPDATING.md#experimental-api-will-deny-all-request-by-default

Source: BSI WID Portal

Vendors and products

• Apache Software Foundation Apache Airflow
• Fortinet Fortinet FortiAnalyzer

Weakness classes (CWE)

• CWE-306Missing Authentication for Critical Function

  Base

  The product does not perform any authentication for functionality that requires a provable user identity or consumes a significant amount of resources.

  Entry at MITRE CWE-306

• CWE-1188Initialization of a Resource with an Insecure Default

  Base

  The product initializes or sets a resource with a default that is intended to be changed by the product's installer, administrator, or maintainer, but the default is not secure.

  Entry at MITRE CWE-1188

• CWE-1056Invokable Control Element with Variadic Parameters

  Base

  A named-callable or method control element has a signature that supports a variable (variadic) number of parameters or arguments.

  Entry at MITRE CWE-1056

References & sources

• fortiguard.fortinet.comFortinet Security Advisory vom 2022-06-07BSI
• lists.apache.orgthread.html/r53d6bd7b0a66f92ddaf1313282f10fec802e71246606dd30c1…web, x_refsource_MISC, Mailing list, Vendor advisory
• GitHub Security Advisoriesadvisories/GHSA-m6h2-jx9v-58w6advisory
• NVD (NIST)vuln/detail/CVE-2021-35936web
• github.comapache/airflow/commit/27265516d2b897585f5019ecd820cfe5471fd351web
• github.comapache/airflow/commit/7a5bb88ad78d600fbb1676a55752597928115bd8web
• github.comapache/airflow/commit/d772f38f843b9add5319a01cf51a844145b01f63web
• github.comapache/airflowpackage
• github.comapache/airflow/compare/2.1.1...2.1.2web
• github.compypa/advisory-database/tree/main/vulns/apache-airflow/PYSEC-202…web
• lists.apache.orgthread.html/r4656959c8ed06c1f6202d89aa4e67b35ad7bdba5a666caff3f…web, x_refsource_MISC, Issue tracking, Mailing list, Vendor advisory
• lists.apache.orgthread.html/r2892ef594dbbf54d0939b808626f52f7c2d1584f8aa1d81570…web
• lists.apache.orgthread.html/r4656959c8ed06c1f6202d89aa4e67b35ad7bdba5a666caff3f…web
• lists.apache.orgthread.html/r2892ef594dbbf54d0939b808626f52f7c2d1584f8aa1d81570…web
• openwall.com[oss-security] 20201211 CVE-2020-17515: Apache Airflow Reflected XSS via Origin Parameterweb, Mailing list, x_refsource_MLIST, Mailing list, Vendor advisory
• lists.apache.orgthread.html/r2892ef594dbbf54d0939b808626f52f7c2d1584f8aa1d81570…web
• lists.apache.orgthread.html/ra8ce70088ba291f358e077cafdb14d174b7a1ce9a9d86d1b33…web
• openwall.com[oss-security] 20210501 CVE-2021-28359: Apache Airflow Reflected XSS via Origin Query Argument in URLweb, Mailing list, x_refsource_MLIST, Mailing list, Third-party advisory
• lists.apache.orgthread.html/rc005f4de9d9b0ba943ceb8ff5a21a5c6ff8a9df52632476698…web
• GitHub Security Advisoriesadvisories/GHSA-86vp-x3pr-79rxadvisory