Curl-url-file-3a-2f-2f-2f ((link))

On Windows installations, curl allows you to swap the third slash or add a drive letter immediately following the authority divider, ensuring cross-platform utility for automation scripts.

While curl is widely known for pulling files down from remote web servers over HTTP or HTTPS , the underlying libcurl library natively supports the file:// protocol . Engineers leverage this functionality for several distinct use cases:

This position has been tested repeatedly. When a path traversal vulnerability in curl file:// handling was disclosed on HackerOne with (no authentication required, any attacker can craft a malicious URL), the curl team maintained their classification despite external disagreement.

On Windows, the syntax can include drive letters, such as file:///C:/Users/name/file.txt . Security Risks: Arbitrary File Read and SSRF curl-url-file-3A-2F-2F-2F

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When passing a URL as a parameter to an API, the system may double-encode the colons and slashes, turning a standard file path into the encoded string 3A-2F-2F-2F .

If you want to copy a file from one directory to another using cURL: curl file:///home/user/document.txt -o /tmp/document.txt Use code with caution. 3. Using Encoded Syntax ( curl-url-file-3A-2F-2F-2F ) On Windows installations, curl allows you to swap

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

This is a command designed to use curl to retrieve the contents of a file located using the file:// protocol, with three slashes after the protocol name.

The debate between the curl development team's position ("this is expected behavior, not a security flaw") and the security community's concerns ("this feature is too dangerous for applications that accept user input") is likely to continue. What is not disputed is that anyone using cURL—especially in application contexts—must be aware of what file:// can do and take appropriate precautions. When a path traversal vulnerability in curl file://

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. Standard: curl file:///etc/passwd

This prevents file:// from ever being honored.

Why write file:/// as file%3A%2F%2F%2F ? This is where URL encoding, also known as percent-encoding, comes into play. Certain characters, such as the colon ( : ) and forward slash ( / ), have reserved meanings in URLs. The colon separates the protocol from the rest of the address, while forward slashes denote different parts of the path.

| Use Case | Reason | |----------|--------| | Testing scripts | Same command works for http:// and file:// | | Fetching configs | curl file:///path/config.json | | Mixing sources | Download from web + read local fallback | | Debugging | See how your tool handles file:// URIs |

curl -X POST -T curl-url-file-3A-2F-2F-2Fexample.txt http://example.com/upload