Apple macOS/iOS - NSUnarchiver Heap Corruption Due to Lack of Bounds Checking in [NSBuiltinCharacterSet initWithCoder:]

EDB-ID:

42050




Platform:

Multiple

Date:

2017-05-23


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Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1170

Via NSUnarchiver we can read NSBuiltinCharacterSet with a controlled serialized state.
It reads a controlled int using decodeValueOfObjCType:"i" then either passes it to
CFCharacterSetGetPredefined or uses it directly to manipulate __NSBuiltinSetTable.
Neither path has any bounds checking and the index is used to maniupulate c arrays of pointers.

Attached python script will generate a serialized NSBuiltinCharacterSet with a value of 42
for the character set identifier.

tested on MacOS 10.12.3 (16D32)


Proof of Concept:
https://github.com/offensive-security/exploitdb-bin-sploits/raw/master/bin-sploits/42050.zip