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95 lines
4.2 KiB
Markdown
95 lines
4.2 KiB
Markdown
# Google CTF 2018 - Shall We Play a Game?
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{% hint style="success" %}
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Learn & practice AWS Hacking:<img src="/.gitbook/assets/arte.png" alt="" data-size="line">[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)<img src="/.gitbook/assets/arte.png" alt="" data-size="line">\
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Learn & practice GCP Hacking: <img src="/.gitbook/assets/grte.png" alt="" data-size="line">[**HackTricks Training GCP Red Team Expert (GRTE)**<img src="/.gitbook/assets/grte.png" alt="" data-size="line">](https://training.hacktricks.xyz/courses/grte)
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<details>
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<summary>Support HackTricks</summary>
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* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
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* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** us on **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks\_live)**.**
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* **Share hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.
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</details>
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{% endhint %}
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Download the APK here:
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I am going to upload the APK to [https://appetize.io/](https://appetize.io) (free account) to see how the apk is behaving:
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.png>)
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Looks like you need to win 1000000 times to get the flag.
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Following the steps from [pentesting Android](./) you can decompile the application to get the smali code and read the Java code using jadx.
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Reading the java code:
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.png>)
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It looks like the function that is going print the flag is **m().**
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## **Smali changes**
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### **Call m() the first time**
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Lets make the application call m() if the variable _this.o != 1000000_ to do so, just cange the condition:
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```
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if-ne v0, v9, :cond_2
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```
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to:
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```
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if-eq v0, v9, :cond_2
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```
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.png>)
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.png>)
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Follow the steps of [pentest Android](./) to recompile and sign the APK. Then, upload it to [https://appetize.io/](https://appetize.io) and lets see what happens:
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.png>)
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Looks like the flag is written without being completely decrypted. Probably the m() function should be called 1000000 times.
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**Other way** to do this is to not change the instrucction but change the compared instructions:
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.png>)
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**Another way** is instead of comparing with 1000000, set the value to 1 so this.o is compared with 1:
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.png>)
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A forth way is to add an instruction to move to value of v9(1000000) to v0 _(this.o)_:
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.png>)
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.png>)
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## Solution
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Make the application run the loop 100000 times when you win the first time. To do so, you only need to create the **:goto\_6** loop and make the application **jump there if `this.o`** does not value 100000:
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.png>)
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You need to do this inside a physical device as (I don't know why) this doesn't work in an emulated device.
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{% hint style="success" %}
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Learn & practice AWS Hacking:<img src="/.gitbook/assets/arte.png" alt="" data-size="line">[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)<img src="/.gitbook/assets/arte.png" alt="" data-size="line">\
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Learn & practice GCP Hacking: <img src="/.gitbook/assets/grte.png" alt="" data-size="line">[**HackTricks Training GCP Red Team Expert (GRTE)**<img src="/.gitbook/assets/grte.png" alt="" data-size="line">](https://training.hacktricks.xyz/courses/grte)
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<details>
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|
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<summary>Support HackTricks</summary>
|
|
|
|
* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
|
|
* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** us on **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks\_live)**.**
|
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* **Share hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.
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</details>
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{% endhint %}
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