The underlying vulnerability typically manifests as a Server-Side Request Forgery (SSRF) flaw.
. Attackers use these sequences to "break out" of the intended web directory and navigate the server's internal file system. /proc/self/environ callback-url-file-3A-2F-2F-2Fproc-2Fself-2Fenviron
: A virtual path on Linux operating systems that contains the environment variables configuration for the currently running process. The Security Vulnerabilities Behind the Payload callback-url-file-3A-2F-2F-2Fproc-2Fself-2Fenviron
In plain English, it’s a command that tries to trick a server into "calling back" to its own internal files—specifically its environment variables —and handing them over to an outsider. callback-url-file-3A-2F-2F-2Fproc-2Fself-2Fenviron