Callback-url-file-3a-2f-2f-2fhome-2f-2a-2f.aws-2fcredentials 2021

callback-url-file-3A-2F-2F-2Fhome-2F-2A-2F.aws-2Fcredentials → callback-url-file:///home/*/.aws/credentials

The most effective way to protect local credentials files is to ensure they do not exist on production servers. The redirect and authorization endpoint - Amazon Cognito

Once an attacker extracts an active aws_access_key_id and aws_secret_access_key , they can bypass perimeter firewalls entirely. They can issue direct API requests via the AWS CLI from any remote machine.

: In OAuth 2.0 and API systems, a callback URL (or redirect URI) tells the server where to send an authorization code or data payload after completing an action. callback-url-file-3A-2F-2F-2Fhome-2F-2A-2F.aws-2Fcredentials

If for some reason file:// callbacks must be supported (not recommended), never allow wildcards or path traversal sequences. Normalize the path and check that it stays within an allowed sandbox directory.

: URL-decoded ( %2F*%2F ), this translates to /home/*/ , targeting standard Linux user home directories.

Most developers know to block http:// and https:// for callback URLs that aren't their own domain. But many forget about file:// . callback-url-file-3A-2F-2F-2Fhome-2F-2A-2F

: This is the URL-encoded representation of :/// .

When an attacker passes a URL-encoded string like file:///home/ubuntu/.aws/credentials into a vulnerable callback-url field, they are leveraging an SSRF vulnerability to achieve a .

: The target application parameter responsible for handling post-authentication redirect URIs . : In OAuth 2

The final part of the URL, credentials , points to a specific file within the .aws directory. The credentials file is a text file that stores AWS access keys and other authentication details. This file is used by AWS CLI and SDKs to authenticate requests.

Use static analysis tools (SAST) to detect dangerous URI scheme usage in source code. Dynamic scanning (DAST) can fuzz callback parameters with file:// payloads to test for vulnerabilities.

[default] aws_access_key_id = AKIAIOSFODNN7EXAMPLE aws_secret_access_key = wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY Use code with caution. Severe Architectural Risks

Imagine a CI/CD pipeline tool that allows users to specify a callback URL to receive build notifications. The tool runs on a Linux server with AWS credentials stored in ~/.aws/credentials (e.g., for deploying artifacts to S3). An attacker, aware of this configuration, supplies the following payload in a webhook registration form: