Curl-url-file-3a-2f-2f-2f -

The keyword "curl-url-file-3A-2F-2F-2F" refers to a URL-encoded representation of the curl command using the file:/// protocol handler. In URL encoding, the character : is represented as %3A and / as %2F. Thus, the string decodes to file:///, which is the standard URI scheme for accessing files on a local file system.

While curl is primarily known for network transfers (HTTP, FTP, etc.), its support for the FILE protocol is a powerful, though often overlooked, feature that carries significant security implications. Understanding the file:/// Protocol in curl

The file:/// scheme allows a user to "fetch" data from their own computer’s storage as if it were a remote server. This is useful for testing scripts locally or automating tasks that involve reading local system files. Syntax Example: Standard: curl file:///etc/passwd

Encoded: curl file%3A%2F%2F%2Fetc%2Fpasswd (often used in web-based parameters or logs) curl-url-file-3A-2F-2F-2F

On Windows, the syntax can include drive letters, such as file:///C:/Users/name/file.txt. Security Risks: Arbitrary File Read and SSRF

The primary danger associated with this keyword is its use in Server-Side Request Forgery (SSRF) attacks. If a web application allows users to provide a URL that is then processed by a backend curl (or libcurl) instance, an attacker can use the file:/// protocol to read sensitive local files from the server. curl overwrite local file with -J - CVE-2020-8177

5. Important Limitations

| Issue | Detail | |-------|--------| | No directory listing | curl file:///home/ → error (unlike file:// in a browser) | | No globbing | curl file:///tmp/*.txt won’t expand; use shell glob first | | Permissions | Must have read access to the file | | No network | Works offline (local files only) | | No recursive download | Use cp -r or tar for directories | Output: curl: (3) URL using bad/illegal format or

2. Using curl with Local Files

Normally, curl works with HTTP/HTTPS. But it also supports the file:// protocol.

Attempt 1: The exact decoded command

curl file:///

Output: curl: (3) URL using bad/illegal format or missing URL

Attempt 3: List directory contents (requires special handling)

curl cannot list directories natively. Use --ftp-method for FTP, but for file://, you need a URL that points to a directory with a trailing slash and rely on libcurl’s fallback. Better yet, use ls. This limitation is why file:/// alone fails. file:// – protocol for local files / after

Guide: Using curl with the file:// Protocol

1. What is file:///?

The string url-file-3A-2F-2F-2F is URL-encoded text.

| Encoded | Decoded | Meaning | |---------|---------|---------| | file%3A%2F%2F%2F | file:/// | File URI scheme |

So file:///etc/passwd means “the file /etc/passwd on this computer”.