28 Jun

Bugs in Enigma Virtual Box

While working on a new version of my static EnigmaVB unpacker, I tried to generate test files to cover most of the Enigma Virtual Box features. In the process, I ran into quite a few bugs in Enigma Virtual Box v7.40.

So, here's a short list:

Registry virtualization

1. Importing REG file with wrapped lines:

Data get truncated at the end of first line.

2. Importing REG file with entry type REG_NONE:

It gets virtualized as a string value "hex(0):"

File virtualization

1. If size of any embedded file > 4GB: creates invalid x86 executable;
2. If total size of all embedded files > 4GB: creates invalid x86 executable;
3. If size of main EXE > 2 GB: creates executable that seems to be valid but won't run;
..and that's only for x86 executables. I wonder how many more issue will surface when I start testing x64 executables. wink

TLS callbacks

Since Enigma Virtual Box uses TLS callbacks to initialize its hooks and handlers, it will (accidentally?) break any executable that also uses TLS callbacks. However, it preserves TLS StartAddressOfRawData, EndAddressOfRawData and AddressofIndex fields. Very weird.. smile

Have fun (and remember to test your software properly)!

20 Jun

Six-factor authentication (it’s not)

Today I read an article in The Register called Tor torpedoed! Tesco Bank app won't run with privacy tool installed.

It's a fun read about Tesco's Android banking app and how it refuses to run when Tor application is installed on your mobile. But what really caught my attention, is this comment to the article:

I did a count of my account with a certain bank and when I use a PC which does not store their funky cookies, I get 6 (yes really, 6) steps for authentication.

  • Initial Customer code
  • Security password as there is no cookie so PC is not recognised
  • pre-agreed image
  • pre-agreed phrase
  • Customer Number
  • Security code

and if I use a Windows PC it whinges that I don't have cRapport which would 'improve my security'
So 6-Factor security isn't good enough and you want an extra package to help???????

Sir, if you ever read what a multi-factor authentication is, you wouldn't be stating such nonsense. All six of the steps you mentioned are of the same factor - "something you know". As such, they provide no additional security, as one keylogger/screengrabber will capture them all.

Why your bank insists on you jumping over so many redundant hoops, remains a mystery..

08 Jun

What’s wrong with this file – ASLR is tricky!

I love magic tricks. My absolute favorites are "there's nothing up my sleeve" kind of tricks. You can look at the equipment, you can examine magicians outfit, everything seems fine - yet the rabbit magically appears and disappears.

Here's a similar reversing challenge for you: https://www.mediafire.com/?38evlc6gmyieskn

This EXE file contains relocations. It has all the necessary necessary flags in PE header. And it gets ASLR support in Windows 10, as you can see in picture:
win10_has_aslr
But on Windows 7/8.1 this poor executable will be always loaded at it's preferred imagebase 0x400000, and doesn't get ASLR support:
win7_no_aslr
Can you figure out what's so special about it? smile

I will provide the correct answer in one week. Or you can provide your opinions in comments. Extra respect awarded for detailed answers and explaining how you figured that out. Extra extra respect if you knew the answer even before looking at the executable. smile

06 Jun

CFF bug in RVA2Offset

Yes, this is yet another post about bugs in CFF Explorer. So far I've described:

Today, I'll describe an issue with CFF Explorer's RVA2Offset function and provide a solution to the problem (patched executable).

And no, I really don't hate CFF Explorer. In fact, it's one of my favorite tools and I use it every day - that's why I keep noticing more and more issues with it. wink

Introduction

Here is an executable that demonstrates the bug: https://www.mediafire.com/?9ju0cfm36b32ys9

If you open it in CFF Explorer and try to check Import Directory. In this case, CFF will show that it's empty.

cff_bug_empty_imports

That's incorrect, import directory of this executable is present and valid. It contains 2 DLLs and 3 APIs:

actual_imports

In other executables, it can get stuck into eternal loop or - even worse - show incorrect data.

Also, CFF's Address Converter feature is affected. In my demo executable, try convert RVA 0x2000 to file offset. It will return 0:

CFF_address_converter_bug

So, what's happening here?

Background of the bug

To put it simply, bug is triggered when one section in executable has SizeOfRawData much larger than VirtualSize. In my crafted executable it looks like this:

CFF_cause_of_bug

Nitpickers corner: it's actually more complicated. The exact condition is ALIGN_UP(sec.SizeOfRawData, pe.FileAlignment) > ALIGN_UP(sec.VirtualSize, pe.SectionAlignment). But who cares about those small details, anyway?

And the offending pseudo-code in CFF Explorer looks something like this:

Fixing the bug

Since I'm doing binary patches to CFF Explorer, I'm quite limited to what I can do and how. In the end, I chose the following pseudocode:

While it doesn't look like much (and it doesn't cover edge cases, for example, when PE file is truncated), in general it should work just fine.

Download link for fixed CFF Explorer: https://www.mediafire.com/?5eg1bs9a9bv39ge
It also includes all my previous fixes.

Conclusion

While writing this post, I noticed that PE viewer in ExeinfoPE v0.0.4.1 has very similar bug. And ProtectionID v6.6.6. And PETools 1.5 Xmas edition. And Stud_PE 2.1. And LordPE. And then I ran out of tools to test. bigsmile

Obviously, I can't fix them all. All I can say - use PE editing/viewing tools that actually work, for example, HIEW or IDA. And when you're writing your own PE parser library, make sure you test it on weird executables.

Have fun and stay safe!

Further reading

03 Jun

Quickpost: addicted to meaningless jargon

This is a great article about one journalist's experiences in the RISE conference.

“We visually organize your email and cloud-based content for ultra fast access,” says Kalpesh, reading from his promotional materials. “It’s visual storytelling with any type of content.”

Say what? What does this thingy do? I have no clue.

Apparently I'm not alone. Luckily, article author translated it to plain English:

Translation: Cubes is actually an app that pinpoints anything that’s not plain-Jane text in your email or Dropbox accounts (a photograph, an excel file, a YouTube video), takes snapshots of those things, and then bundles them together in a standalone app.

OK, now I get it. Thanks! smile

However, the sad thing is, it's not just startups. If you're working in a large company, you've probably seen these kinds of emails sent by your pointy-haired bosses. They are stuck in their bubbles talking about "disruption", "alignment" and "engagement". How about this:

To ensure synergies and alignment between the finance strategy and business needs, Mr.X will co-operate closely with all finance functional leads, including aligning closely with Mr.Y and his team to ensure the consistent dissemination of financial information.

No, I really don't know why our company is going to pay $100k a year to this guy. Do you?