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Points: 977 [1000]

Description

Korovax would like to keep its users informed about the latest updates of COViD, and there’s nothing better but to spam your emails!

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Solution

1. As a continuation from mobile/Contact Us!, we continue to analyze the code from sg.gov.tech.ctf.mobile.Contact.ContactForm.java
2. Unlike mobile/Contact Us!, it appears we have to look at the native functions that are called within the .java class itself.

    public native int check(String str);
   
    public native String retrieveFlag();
   
    public native int retrieveFlag2(String str, int i);
   

3. Googling about native functions tells us that there is usually a dynamic library attached to the program. In this case, there appears to be a libnative-lib.so attached in the apk at resource/lib/<archtecture types>/.
4. Opening the file in Cutter and scrolling through the functions, we will see the three functions above. When we click on sym.Java_sg_gov_tech_ctf_mobile_Contact_ContactForm_check, we can see a neat little flag sitting there.

Flag

govtech-csg{th3rE_15_nO_n0bIliTy_In_p0Vert7}

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