Accéder au contenu principal

ASIS CTF Quals 2015 - Sawthis Writeup - Srand Remote Prediction


The remote service ask for a name, if you send more than 64 bytes, a memory leak happens.
The buffer next to the name's is the first random value used to init the srand()


If we get this value, and set our local srand([leaked] ^ [luckyNumber]) we will be able to predict the following randoms and win the game, but we have to see few details more ;)

The function used to read the input until the byte \n appears, but also up to 64 bytes, if we trigger this second condition there is not 0x00 and the print shows the random buffer :)

The nickname buffer:



The seed buffer:



So here it is clear, but let's see that the random values are computed with several gpu instructions which are decompiled incorrectly:







We tried to predict the random and aply the gpu divisions without luck :(



There was a missing detail in this predcitor, but there are always other creative ways to do the things.
We use the local software as a predictor, we inject the leaked seed on the local binary of the remote server and got a perfect syncronization, predicting the remote random values:




The process is a bit ugly becouse we combined automated process of leak exctraction and socket interactive mode, with the manual gdb macro.




The macro:



















Related news

Commentaires

Posts les plus consultés de ce blog

HTML5 Games On Android

On my last hollidays, I made two HTML5 games, and published on android market. Nowadays javascript has powerful libraries for doing almost everything, and also there are several compilers from java or c code to javascript, converting opengl c code to html5 canvas, but definitely, javascript execution is slower than dalvik applications, and of course much slower than arm c libs. For improving the speed of sounds and images loader, I have used javascript asynchronous execution and scheduling priority has been controlled with setTimeout/setInterval which deprioritize or priorize a code block. This games are published on the android market here: Android Planets and here: Far Planet Related news Hacker Hardware Tools Pentest Tools Port Scanner Hacker Tools For Mac Tools Used For Hacking Hacker Techniques Tools And Incident Handling Easy Hack Tools Hacking Tools Kit Hacking Tools Usb Hacker Hardware Tools Hacker Tools Hardware Hack Tools For Windows Hacking Tools For G...

BeEF: Browser Exploitation Framework

"BeEF is the browser exploitation framework. A professional tool to demonstrate the real-time impact of XSS browser vulnerabilities. Development has focused on creating a modular structure making new module development a trivial process with the intelligence residing within BeEF. Current modules include the first public Inter-protocol Exploit, a traditional browser overflow exploit, port scanning, keylogging, clipboard theft and more." read more... Website: http://www.bindshell.net/tools/beef Related links Pentest Automation Tools Ethical Hacker Tools Hacking Tools For Windows Free Download Pentest Reporting Tools Hack Tool Apk No Root Nsa Hack Tools Download Beginner Hacker Tools Hacking Tools For Windows Free Download Hack Tools For Mac Hack Tool Apk No Root Kik Hack Tools Hacking App Pentest Tools List Nsa Hacker Tools Hack Tools Mac Hacking Tools Kit Pentest Tools For Android Hack Tools For Windows Hackrf Tools Tools 4 Hack Hacking Tools Mac Hacking ...

Abdominal pain after a motor vehicle accident

CASE A 22-year-old man was brought to the ED complaining of abdominal pain after a rollover motor vehicle accident. He was the front seat passenger and was wearing a seat belt. Although he was trapped in the vehicle and it caught on fire, he did not suffer any cutaneous burns. History  The patient's past medical history was significant for attention-deficit hyperactivity disorder. He admitted to using tobacco and alcohol socially, but denied illicit drug use. He denied any medication use or drug allergies. A review of systems was positive for complaints of abdominal pain and anxiety. Physical examination  The patient's vital signs were: BP, 112/51 mm Hg; heart rate, 110 beats/minute; respirations, 23; SpO 2 , 95% on room air; and temperature, 37.4° C (99.3° F). On ED arrival, he was awake, alert, and oriented but appeared anxious and agitated. His pupils were equal, round, and reactive to light. His head was normocephalic with a 2-cm laceration on the left ear. The pati...