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

It looks like you are working with a Local File Inclusion (LFI) Server-Side Request Forgery (SSRF) payload designed to exfiltrate AWS credentials. The URL encoded string file-3A-2F-2F-2Fhome-2F-2A-2F.aws-2Fcredentials translates to file:///home/*/.aws/credentials

. This is a classic security research pattern used to demonstrate how an application might inadvertently leak sensitive configuration files.

Below is a draft post formatted for a technical audience (like on Security Blog ) that explains this vulnerability.

Security Alert: Preventing AWS Credential Leakage via SSRF/LFI

I’ve been looking into how common "callback URL" parameters can be weaponized to exfiltrate sensitive cloud metadata. A common payload I'm seeing in logs looks like this: ?callbackUrl=file:///home/*/.aws/credentials 🔍 What is happening? Attackers use the

protocol to trick an application into reading local files instead of fetching a remote URL. If the application has enough permissions, it may return the contents of the AWS credentials file, exposing: Access Key IDs Secret Access Keys Session Tokens 🛡️ How to Protect Your Infrastructure Validate Protocol Schemes : Only allow for callback URLs. Explicitly block Use an Allowlist

: Don’t just "sanitize" input. Only permit callbacks to a strict list of pre-approved domains. : If you are on EC2, enforce Instance Metadata Service Version 2 (IMDSv2)

. It requires a session token, making it much harder for SSRF to steal credentials. Least Privilege callback-url-file-3A-2F-2F-2Fhome-2F-2A-2F.aws-2Fcredentials

: Ensure your application's IAM role has the absolute minimum permissions required. Never run web servers as the 💡 Pro-Tip for Researchers

If you are testing this in a bug bounty program, always use a Canary Token or a benign file like /etc/hostname

first to prove the vulnerability without touching sensitive production secrets. #CyberSecurity #AWS #CloudSecurity #AppSec #BugBounty #SSRF If you'd like to tailor this further, let me know: Who is the target audience

? (e.g., developers, C-level executives, or security researchers) What is the

of the post? (e.g., educational, a security advisory, or a "look what I found" post) code snippets for a specific fix (like in Python/Node.js)?

It is not possible to write a meaningful, long-form article about the specific string callback-url-file-3A-2F-2F-2Fhome-2F-2A-2F.aws-2Fcredentials as a legitimate technology keyword or standard.

Here is why, followed by what you likely need to know instead. It looks like you are working with a

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.

The "Home/*" Wildcard

Notice the * in /home/*/.aws/credentials. Attackers use this because they don’t know if the app runs as ubuntu, ec2-user, admin, or user.

By using a wildcard (or attempting path traversal like ../../*), they hope the application logic will resolve the path globally.

8. Comparison with Standard Callbacks

| Feature | HTTP callback (http://localhost) | File callback (file://) | |---------|--------------------------------------|----------------------------| | Port required | Yes | No | | Browser redirect works | Yes | No (needs OS handler) | | Supports multiple profiles | Via query params | Via file section parsing | | Security | Localhost bound | Filesystem permissions | | Ease of debugging | Network logs | File write logs | Callback URL : A callback URL is a

Step 4 – CLI uses credentials

The tool reads the updated credentials file and uses it for AWS API calls.

Final Thought

If you are scanning your codebase for "callback-url-file-3A-2F-2F-2Fhome-2F-2A-2F.aws-2Fcredentials" and found it in a log file but not in your source code—it means someone probed you.

Check your access logs. Check your SSRF filters. And for the love of Bezos, don’t let your servers read local files via callback URLs.

Have you seen similar file:// callback attempts in the wild? Share your war stories in the comments below.

3. Why you are seeing this string

You likely encountered this string in one of three places:

  1. Web Server Logs – Someone attempted to exploit your application by injecting this string as a redirect URL or callback parameter.
  2. A Security Scanner Report (e.g., Burp Suite, OWASP ZAP, Nessus) – The scanner automatically generated this to test for path traversal or SSRF vulnerabilities.
  3. A Malformed OAuth/Login Configuration – You may have incorrectly configured an OAuth callback URL in a development environment, and the system URL-encoded the path.

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.

Step 3 – Writing credentials to file

The callback “handler” (OS-level helper or CLI daemon) interprets the file:// scheme: