Threat Level: green Handler on Duty: Renato Marinho

SANS ISC: VBA and P-code SANS ISC InfoSec Forums

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VBA and P-code

I want to draw your attention to some great work Dr. Bontchev did.

pcodedmp.py is a VBA P-code disassembler. Microsoft Office documents contain VBA macros in several forms. They contain the source code, but also compiled P-code. Dr. Bontchev created a proof-of-concept document that executes P-code and does not contain the corresponding source code. Here is the output from his pcodedmp.py tool for his PoC document:

python pcodedmp.py -d poc2b.doc

Processing file: poc2b.doc
===============================================================================
Module streams:
Macros/VBA/ThisDocument - 1949 bytes
Line #0:
        FuncDefn (Sub / Property Set) func_00000078
Line #1:
        LitStr 0x001D "This could have been a virus!"
        Ld vbInformation
        Ld vbOKOnly
        Add
        LitStr 0x0006 "Virus!"
        ArgsCall MsgBox 0x0003
Line #2:
        LitStr 0x0008 "calc.exe"
        Paren
        ArgsCall Shell 0x0001
Line #3:
        EndSub

 

Dr. Bontchev also coded a plugin for oledump.

Didier Stevens
Microsoft MVP Consumer Security
blog.DidierStevens.com DidierStevensLabs.com

DidierStevens

464 Posts
ISC Handler
Sep 26th 2016
Do you know if the AV vendors tend to scan for Malware/Viruses based on Source of P-code content ?
Anonymous
sorry, should have been "Source OR P-Code content ?"
Anonymous
From the few tests that I did, I say source code.
DidierStevens

464 Posts
ISC Handler

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