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

Attackers often pass URL-encoded strings into web applications to bypass simple text filters. If an application blocks the word file:/// , an attacker might try file%3A%2F%2F%2F to trick the application into executing the command anyway. Security Implications: The Threat of LFI and SSRF

To understand the whole, we must first break it down:

. If an application takes a URL as input and passes it to cURL without strict validation, an attacker can provide a URL to read sensitive system files, such as: /etc/passwd on Linux systems.

Next time you see %3A%2F%2F in the wild, you will not see chaos. You will see a colon, three slashes, and a story of how the web’s simplest tools can become its most dangerous attack surface—if left unchecked. curl-url-file-3A-2F-2F-2F

To resolve issues where this encoded string appears, the following steps are generally taken:

# Encoded version of curl file:///etc/passwd encoded="file%3A%2F%2F%2Fetc%2Fpasswd" curl "$encoded"

curl file:///absolute/path/to/file

Using three slashes ( file:/// ) is standard for absolute paths on Unix-based systems, but misquoting the string in a terminal can cause the shell to mangle the special characters.

Reason? curl expects a fully qualified path after file:/// . A dangling triple slash points to a directory, and by default, curl does not perform directory listing. However, the true danger emerges when you append a valid file path:

To help me tailor more relevant technical insights, tell me a bit more about how you encountered this string: If an application takes a URL as input

curl [options] URL

: To read a file on the C: drive (note the use of forward slashes): curl file:///C:/Users/Public/Documents/log.txt Use code with caution. Common Use Cases