Fetch-url-file-3a-2f-2f-2froot-2f.aws-2fconfig Jun 2026

SSRF occurs when a web application takes a user-supplied URL, fails to validate it, and commands the backend server to make an HTTP or file request to that URL.

: The target file path. In AWS environments, this file often contains sensitive information like AWS Access Keys, Secret Keys, and region settings for the root user. Why This is Significant

Then replace each 2F with / :

If an attacker reads files from the instance, they will find no long-term keys. However, they might still access the IMDS endpoint – so secure IMDSv2 with hop limits and disable IMDSv1. fetch-url-file-3A-2F-2F-2Froot-2F.aws-2Fconfig

If the application fails to restrict requests to external web addresses ( http:// or https:// ), the backend server will parse the file:// schema natively. If the web server process happens to run with root privileges, the application reads the system's root directory and prints the contents of .aws/config right back to the attacker. How to Detect and Remediate SSRF Attacks

: Developers should disable unused protocols like file:// in their HTTP clients and use allow-lists for specific external domains. AWS and HackerOne CTF write-up - Pawel Rzepa

Sanitize and validate all user inputs in web applications. Never allow end-user inputs to directly dictate the backend's URL-fetching or file-retrieval mechanisms (e.g., disallowing the file:// scheme entirely). SSRF occurs when a web application takes a

The following example demonstrates how a poorly configured back-end script allows this type of file fetching exploit to succeed:

In a typical SSRF vulnerability, an attacker leverages a server's "fetch" or "URL preview" functionality to make internal requests. By using the protocol instead of http:// , the attacker instructs the server to read its own local filesystem. Path Targeted: /root/.aws/config

On an AWS EC2 instance, the .aws directory typically contains two critical files: Why This is Significant Then replace each 2F

Never allow the file-fetching function to use arbitrary URI schemes. Explicitly enforce that only http or https protocols are permitted. Implement Input Sanitization

[profile prod] aws_access_key_id = YOUR_PROD_ACCESS_KEY aws_secret_access_key = YOUR_PROD_SECRET_KEY region = us-west-2

To understand this exploit attempt, it helps to break down the text into its functional components. Cybercriminals use URL encoding to disguise commands and bypass basic security filters like Web Application Firewalls (WAFs).

If your web server runs as www-data (non-root), an attacker exploiting file:// cannot read /root/.aws/config because the process lacks permissions. Follow the principle of least privilege: