loknop

Solving "includer's revenge" from hxp ctf 2021 without controlling any files

The challenge

The challenge was to achieve RCE with this file:

<?php ($_GET['action'] ?? 'read' ) === 'read' ? readfile($_GET['file'] ?? 'index.php') : include_once($_GET['file'] ?? 'index.php');

Some additional hardening was applied to the php installation to make sure that previously known solutions wouldn't work (for further information read this writeup from the challenge author).

I didn't solve the challenge during the competition - here is a writeup from someone who did - but since the idea I had differed from the techniques used in the published writeups I read (and I thought it was cool :D), here is my approach.

fnky

ANSI Escape Sequences

Standard escape codes are prefixed with Escape:

• Ctrl-Key: ^[
• Octal: \033
• Unicode: \u001b
• Hexadecimal: \x1B
• Decimal: 27

HarmJ0y

# PowerView's last major overhaul is detailed here: http://www.harmj0y.net/blog/powershell/make-powerview-great-again/
#   tricks for the 'old' PowerView are at https://gist.github.com/HarmJ0y/3328d954607d71362e3c

# the most up-to-date version of PowerView will always be in the dev branch of PowerSploit:
#   https://github.com/PowerShellMafia/PowerSploit/blob/dev/Recon/PowerView.ps1

# New function naming schema:
#   Verbs:
#       Get : retrieve full raw data sets
#       Find : ‘find’ specific data entries in a data set

amitsaha

How does ls work?

I wanted to be really able to explain to a fair amount of detail how does the program :command:`ls` actually work right from the moment you type the command name and hit ENTER. What goes on in user space and and in kernel space? This is my attempt and what I have learned so far on Linux (Fedora 19, 3.x kernel).

How does the shell find the location of 'ls' ?