NSKeyedUnarchiver - Info Leak in Decoding SGBigUTF8String Exploit

There is an info leak when decoding the SGBigUTF8String class using [SGBigUTF8String initWithCoder:]. This class initializes the string using [SGBigUTF8String initWithUTF8DataNullTerminated:] even though there is no guarantee the bytes provided to the decoder are null terminated. It should use [SGBigUTF8String initWithUTF8Data:] instead.

While this class is included in iMessage, it is more likely that this bug could be useful in local attacks.

To reproduce this issue:

1) Compile decodeleak.m

clang -o decodeleak -g decodeleak.m -fobjc-arc -framework CoreSuggestionsInternals -F/System/Library/PrivateFrameworks

2) Run:

./decodeleaks obj

leaked memory will be printed to the screen.


Proof of Concept:
https://github.com/offensive-security/exploitdb-bin-sploits/raw/master/bin-sploits/47257.zip