Callback-url-file-3a-2f-2f-2fhome-2f-2a-2f.aws-2fcredentials

Understanding the Components

1. Callback URL: A callback URL is a URL that an application redirects to after completing a task or process, often used in OAuth flows. The application (client) redirects the user to a server (authorization server), which then redirects back to the client with an authorization code or token via the callback URL.

2. File Path /home/*/.aws/credentials: This path refers to a file on a Unix-like system (including Linux and macOS) where AWS CLI (Command Line Interface) stores access keys for AWS accounts. The ~/.aws/credentials file is specifically where the AWS CLI looks for credentials by default. The path can be broken down as:

   • /home/: This typically represents the home directory of a user on a Unix-like system. The asterisk (*) likely represents a wildcard for any user.
   • /.aws/: A hidden directory within the user's home directory where AWS CLI stores its configuration and credentials.
   • credentials: A file within the .aws directory that stores the AWS access key ID and secret access key.

3. URL Encoding 3A-2F-2F: The string 3A-2F-2F represents URL-encoded characters:

   • 3A = :
   • 2F = /

   So, 3A-2F-2F translates to :/, which might appear in a URL or path to indicate a protocol and path but seems misplaced or incorrectly represented in your context. callback-url-file-3A-2F-2F-2Fhome-2F-2A-2F.aws-2Fcredentials

Callback Acknowledgment

• Even though it’s a file write, the auth server expects a confirmation (e.g., 200 OK over a dummy HTTP or via log entry).

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The Serious Security Risk: Why this specific string is dangerous

If your software actually interprets callback-url-file:///home/*/.aws/credentials as a valid location to read files from, your system is critically vulnerable.

An attacker who can force your server to read ~/.aws/credentials can steal your Amazon Web Services (AWS) Access Keys. With those keys, the attacker can:

• Delete all your S3 buckets.
• Spin up expensive cryptocurrency mining instances.
• Exfiltrate your entire database.
• Take over your AWS account.

The * wildcard makes it worse – an attacker could potentially read credentials for any system user without knowing the exact username. Understanding the Components

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A Real-World Analogy

Imagine you run a concierge service. You tell the concierge, "Anyone who brings a valid ticket can ask you to read any document."

An attacker hands you a ticket that says: "Read the file at /home/*/.aws/credentials."

If your concierge does it, they just handed over the keys to your castle. Callback URL : A callback URL is a

The file:// callback is that malicious ticket.

1. Feature Overview

Feature name:
Local File URI Callback for Credential Delivery

Callback URL format:
callback-url-file:///home/*/.aws/credentials

Purpose:
Securely deliver temporary AWS credentials (or other tokens) from a web auth flow directly into a local credentials file on disk, using a file-based callback instead of an HTTP local server.

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Atomic Write

• Write to temporary file → rename() to target → prevent partial reads.

How to Fix This (The Developer Checklist)

If you see file:///home/*/.aws/credentials in your logs (or any file:// callback), take immediate action:

1. Explicitly block the file protocol. Your redirect URI validation should only allow https (and http only for localhost debugging).
2. Never use wildcards in file paths for callbacks. Whitelists should be exact strings, not glob patterns.
3. Update your OAuth library. Many older libraries had default "open redirect" vulnerabilities that allowed file:// tricks. Modern versions strip non-HTTP schemes by default.
4. Rotate your AWS keys. If this log entry appeared from an external source (not your own testing), assume the attacker already tried to read that file. Rotate your ~/.aws/credentials immediately.