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Offset2lib: bypassing full ASLR on 64bit Linux



Hi,

This is a disclosure of a weakness of the ASLR Linux implementation.
The problem appears when the executable is PIE compiled and it has an
address leak belonging to the executable. We named this weakness:
offset2lib.

In this scenario, an attacker is able to de-randomize all mmapped
areas (libraries, mapped files, etc.) by knowing only an address
belonging to the application and the offset2lib value.

We have built a PoC which bypasses on a 64 bit Linux system, the three
most widely adopted and effective protection techniques: No-eXecutable
bit (NX), address space layout randomization (ASLR) and stack smashing
protector (SSP). The exploit obtains a remote shell in less than one
second.

We have proposed the ASLRv3 which is a small Linux patch which removes
the offset2lib weakness.

Details of the weakness, steps to exploit the offset2lib weakness, a working
proof of concept exploit, recommendations and a demonstrative video has been
publish at: http://cybersecurity.upv.es/attacks/offset2lib/offset2lib.html


Hector Marco.

http://cybersecurity.upv.es