VirtualBox 5.2.6.r120293 - VM Escape









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Oracle fixed some of the issues I reported in VirtualBox during the Oracle Critical Patch Update - April 2018. CVE-2018-2844 was an interesting double fetch vulnerability in VirtualBox Video Acceleration (VBVA) feature affecting Linux hosts. VBVA feature works on top of VirtualBox Host-Guest Shared Memory Interface (HGSMI), a shared memory implemented using Video RAM buffer. The VRAM buffer is at physical address 0xE0000000 

I didn't see such optimization in VirtualBox for Windows and OSX. Only Linux hosts are affected. 

Find a value in (assume as some fake jump table), which during relative address calculation will point into the 16MB shared VRAM buffer. For the proof-of-concept exploit fill the entire VRAM with NOP's and place the shellcode at the final pages of the mapping. No ASLR bypass is needed since the jump is relative. 

In the guest, add vboxvideo to /etc/modprobe.d/blacklist.conf. vboxvideo.ko driver has a custom allocator to manage VRAM memory and HGSMI guest side implementations. Blacklisting vboxvideo reduces activity on VRAM and keeps the payload intact. The exploit was tested with Ubuntu Server as Guest and Ubuntu Desktop as host running VirtualBox 5.2.6.r120293.

The proof-of-concept exploit code with process continuation and connect back over network can be found at virtualbox-cve-2018-2844