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

callback-url-file:///home/*/.aws/credentials

Alex grinned. "Hey, that's what makes life interesting, right?"

As a developer, you may have stumbled upon a peculiar callback URL while working with AWS services: /home/*/.aws/credentials . At first glance, this URL seems to be related to AWS authentication, but its purpose and structure might be unclear. In this blog post, we'll demystify this callback URL and explore its significance in the context of AWS and authentication.

AWS (Amazon Web Services) provides a comprehensive cloud computing platform that offers a wide range of services. When interacting with AWS services, applications need to authenticate themselves to ensure they're accessing resources securely. AWS credentials, comprising an access key ID and a secret access key, are essential for this authentication.

async function handleCallback(userSuppliedUrl) // axios does not support file:// by default, but a custom adapter might // Or if using 'request' library with allowFileSchemes flag const response = await axios.get(userSuppliedUrl); console.log(response.data); callback-url-file-3A-2F-2F-2Fhome-2F-2A-2F.aws-2Fcredentials

: Use established libraries like OWASP's Security Logging or built-in language parsers to validate that a URL is a valid web address before processing it.

This exploit relies on a multi-step vulnerability chain that bridges misconfigured identity routing with server-side local file read access.

If successful, the attacker gains the identity of the server.

If you are trying to automate a post using AWS services, here are the standard ways to handle it: 1. Using AWS SDKs (Recommended) callback-url-file:///home/*/

While the Capital One breach did not involve a file:// callback vulnerability, it perfectly illustrates the stakes. A misconfigured web application firewall (WAF) allowed an attacker to perform an SSRF attack that read AWS metadata credentials from an internal endpoint ( http://169.254.169.254/latest/meta-data/iam/security-credentials/ ). Those credentials gave access to an S3 bucket containing 100+ million customer records.

To prevent an application from ever being able to read its own credentials via a URL:

Never allow user‑supplied URLs to use arbitrary schemes. Maintain an explicit allowlist:

When decoded, the URL portion translates to file:///home/*/.aws/credentials . This path targets the standardized location where the AWS CLI stores secret access keys . If a web application or OAuth client accepts local file system protocols ( file:// ) within its redirect configurations, malicious actors can leverage this oversight to exfiltrate highly sensitive cloud configuration files. Anatomy of the Payload In this blog post, we'll demystify this callback

– Even if the asterisk isn’t a true wildcard, an attacker might use it to bypass weak filters. For instance, a filter that blocks ../ might not block a wildcard that later gets resolved.

The implementation of home/*/.aws/credentials relies on the host system evaluating the wildcard ( * ) to locate an active user profile folder (e.g., /home/ubuntu/ or /home/admin/ ). If the server's backend parsing language interprets this pattern directly or allows path traversal, it opens the door to access critical cloud credentials. Security Consequences: The Cloud Blast Radius

| 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 |

The Danger in Your Debug Log: Why file:///home/*/.aws/credentials is a Red Flag

home-2F-2A-2F : The URL-encoded path for /home/*/ , targeting user profile directories on Linux-based servers.

[default] aws_access_key_id = AKIAIOSFODNN7EXAMPLE aws_secret_access_key = wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY