02 Jun

Enigma’s EP_CryptDecryptBuffer internals

For one of my private projects, I needed to decrypt some data. Original executable uses Enigma's EP_CryptDecryptBuffer function but I needed to implement the same thing using .NET. Much to my surprise, there was no information about what encryption algorithm is used by Enigma or how it works internally. So, I started by compiling Enigma's sample project CryptBuffer and debugging the executable.

TL;DR - IDEA cipher in CBC mode, password = MD5(user_password), IV for CBC comes from IDEA.Encrypt(8-zeroes, password).

Research

After protecting my executable with Enigma, few assembly lines

got changed into something horrible that looked like an Enigma's VM:

I didn't feel like spending my time on analyzing that. Much easier solution was to put hardware breakpoints on my data and password and wait for them to trigger. In a few seconds I landed into code that looked like MD5 (notice the constants!):

and few hits later I landed into code that I didn't recognize at first:

Delphi compiler had helpfully included RTTI information telling me that this second piece of code belongs to a class called TIdeaCipher. Now I had all the information I needed, I just had to put it all together. smile

Implementing decryption in C#

There aren't many IDEA implementations in C#. In fact, there are 2: by BouncyCastle and by LexBritvin. Since I'm not a big fan of huge and complex libraries like BouncyCastle, so I took the simplest possible code: from Github and modified it a bit.

First, we need change password generation algorithm to use MD5 to generate real password:

Second, we need to add support for CBC mode. It requires both calculating correct IV value and pre/post-processing each block we're encrypting or decrypting.

Calculating IV is quite simple:

Processing each block is slightly harder but not a rocket science either. As explained in image borrowed from Wikipedia:
.

Before decrypting the data block, we need to store the encrypted values as IV for the next block. After decrypting the block, we need to XOR each byte of data with a corresponding byte of IV. Unfortunately, during encryption the data flow is different, so the simple crypt function has to be replaced with 2 functions: encrypt and decrypt.

Few more cosmetic changes and that's it! We got clean and nice implementation of EP_CryptDecryptBuffer in pure C#. smile
Download link: https://bitbucket.org/kao/ep_cryptdecryptbuffer/

Have fun!

P.S. My implementation only supports cases where data length is divisible by 8, adding support for other lengths is left as an exercise for the reader.

12 May

VMProtect and dbghelp.dll bug in export processing

If your Olly is crashing when loading executable protected by VMProtect, you most likely have outdated dbghelp.dll somewhere on your path. Grab the latest version from Microsoft and put it in the Olly folder.

Well, that might be enough to work around the issue that I had - but I still wanted to know what's causing the crash.

Cause of the problem

If you try to debug Olly with another Olly, you'll see the Access Violation happening somewhere in dbghelp.dll:

Check register values in Olly:

For some reason, value in EDX is garbage and therefore access violation happens.

Call stack doesn't tell us much:

And same piece of code in IDA doesn't help much either:

So, it's debugging time! Set breakpoint to start of LoadExportSymbols, then set hardware breakpoint on write to address [ebp+ptrAllocatedMemory].

First hit is initialization of variable with 0:

Second hit stores the address of allocated memory:

And third time is a charm:

Good folks at Microsoft have left us with a nice buffer overflow. exportFunctionName is defined as byte array of size 2048 bytes. Any exported function name longer than that will cause stack overflow and (possibly) subsequent crash.

010Editor with PETemplate confirms that the export name is indeed very long (3100 chars):

From what I can tell, it's a similar (but not the same) bug to what was described by j00ru at http://j00ru.vexillium.org/?p=405 (see "PE Image Fuzzing (environment + process)")

Stay safe!

P.S Here's an example file, if you want to test your Olly: https://forum.tuts4you.com/topic/38963-vmprotect-professional-v-309-custom-protection/
P.P.S. CFF Explorer, HIEW and IDA do not show us any exports in this example file - but that's a matter of another story..

21 Apr

Updated Enigma VirtualBox unpacker again

This update has been long overdue. Finally it supports files larger than 2GB! smile

Full changelog:

  • Supports files larger than 2GB. Yeah!
  • Correctly recognizes EnigmaVB 7.50-7.70;
  • You can use command-line EnigmaVBUnpacker.exe /nogui [pathToFile] to unpack file, save results to !unpacker.log and close automatically.
  • NEW: fixed "Error creating temporary file"

Hopefully I didn't break anything during the rewrite. But if I did, send me an email and I'll fix it! smile

Download link: https://www.mediafire.com/?phu1lxocl3r1b2x

EDIT 2x: Very stupid error fixed. /me embarrassed. Sorry.

24 Mar

Cybellum – next gen cyber company (it’s not)

2 days ago everybody started talking about DoubleAgent attack that Cybellum supposedly invented and how every Windows OS since Windows XP is screwed. As soon as I read about it, I said "hmmm, where have I seen it before?".

While the rest of the world went on writing sensational news articles, Alex Ionescu summed up it all up in one nice tweet:

Have fun and don't believe in everything you read - too many morons are writing about security these days..

09 Mar

Recovering data from faulty HDD

I'm extremely lucky. In my 15+ years of messing with computers, I've never lost data due to HDD developing bad blocks and dying. Never! smile

Other people are not that fortunate. So, last weekend I was asked to look at an Acer laptop that just won't start. Windows startup screen shows up, stays for 5-10 minutes and computer reboots. Safe mode doesn't start, Alt-F10 Acer Recovery Console won't show up, nothing. At least I got Windows Memory Diagnostics to show up - and it didn't find anything wrong with RAM.

After I disabled Automatic Restart on System Failure (and waited 10+ minutes for Windows to crash), I got this nice error UNMOUNTABLE_BOOT_VOLUME (STOP: 0x000000ED):

Considering how much time it takes to get to the error, it's probably a bad hard disk.

Disclaimer: data recovery is a very delicate science. If you value your data, I suggest that you use a specialized data-recovery service. But if you are short on cash or just want to have some fun with dying HDD, please read on! Just remember that each HDD issue is different and what worked for me might not work for you.

Disassembly time!

I removed 2 screws to get access to HDD. First thing I saw was this huge scratch all over HDD bracket and cover plastic.

Apparently Mr.Awesome Neighborhood PC Repair Dude has tried to remove HDD with a screwdriver and failed. He had also broken few plastic clips on HDD cover - but who cares about those, right? At least, he did no visible damage to the electronic parts of HDD. smile

Let's try to attach disk to another PC and see if it's really bad.

Windows hates bad disks

Let me tell you, attaching it to my Windows computer was a bad idea. When disk was plugged in, Windows took 5 minutes to start. Any program took 1-2 minutes to start. To be honest, I have no idea why Windows were acting so weirdly, but hey, kids, don't try this at home! smile

At least I got an output from Crystal Disk Info which confirmed my suspicions - bad HDD:

On the side note, Internet is full of really stupid advices. If you suspect that your disk might be physically damaged and dying, never ever use "chkdsk" or similar tools on it! They will likely fail and/or corrupt your data even more. Make a full disk copy and try to fix data there.

Lesson learned - don't use Windows if your HDD is dying. Linux is much safer and data-recovery friendly!

Clonezilla

After some Googling, I found Clonezilla. It's a free Linux-based software that helps with disk imaging/cloning. Reviews were nice, so I made a bootable USB with Clonezilla and tried it out.

It failed.

After enabling "Expert options" and enabling ––rescue flag, it started to do something. However, estimated completion time of 40+ hours wasn't exactly exciting. Apparently, Clonezilla/partclone is slow! I'd love to have a solution that actually works, preferrably today.

Ddrescue and open-source stupidities

Few more Google searches later I learned about ddrescue. It's yet-another-Linux-software that can do almost anything - iff you can master its arcane command-line arguments. As their "manual" tells it succinctly:

This tutorial is for those already able to use the dd command. If you don't know what dd is, better search the net for some introductory material about dd and GNU ddrescue first.

Dude, I AM reading the ddrescue manual. What other introductory material about ddrescue should I search for? sad

Since ddrescue is included in clonezilla USB image, I launched bash and tried the simplest possible version:

It failed with error "Can't open input file: Permission denied". Apparently, you need to use sudo. My next attempt was actually successful!

So, here we are, after 5 hours of running.. Estimated remaining run time is 25 minutes and it has recovered everything but 100MB of data from the HDD... Fingers crossed!

18 hours later my fingers were still crossed.. WTF?

Well... Hidden in the ddrescue manual is this great note:

The 'remaining time' is calculated using the average rate of the last 30 seconds and does not take into account ... Therefore it may be very imprecise, may vary widely during the rescue, and may show a non-zero value at the end of the rescue. In particular it may go down to a few seconds at the end of the first pass, just to grow to hours or days in the following passes.

Holy fuck, why on earth would you show "remaining time" if you very well know that it's "very imprecise"? Does it make your program go any faster? No. Does it help your user in any way? No. It just pisses everyone off.

All in all, ddrescue ran for around 48 hours - recovering 99.98% of data. There were still 45MB of non-scraped data left but I decided that it's not worth to wait 40-50 more hours to rescue mere 20-30 megabytes.

Lesson learned - reading data from unreadable sectors is really slow. Prepare to wait for days!

Analyze the rescued image

Recovering data is great. But what to do with the 0.02% of data that were unreadable? ddrescue log can tell you that sector 0x12345000 was unreadable - but you will have no idea which file occupied that sector. Since I'm a Windows guy, I decided to modify ddrescue's suggested approach a bit and used Windows tools when possible.

First, run ddrescue with ––fill-mode argument:

It will take the image file and mark all unreadable sectors with "BABEC0DE" and relevant sector/position information based on the log file. The affected part of file will look like this:

You can pick whatever text you want - I didn't want to use suggested "DEADBEEF" constant, as it is much more commonly used and might actually appear in some valid files.

Second, reboot into Windows and use OSFMount to mount the created hdimage.img:

Finally you can see files and folders from the damaged disk. Now use whichever Windows tool you like to search for "BABEC0DE". In my case, there were 16 files affected - 12 videos and 4 log files. So, nothing of value was lost! smile

Write the rescued image to the new hard drive

If you have Acronis or other Windows cloning software, you could use that to write HDD image to new disk. Since I didn't have any, I use Clonezilla's bootable USB and Linux standard dd command:

After an hour and a half all the data were transferred to the new disk. Now I just needed to put HDD back into the laptop, boot up the system and run chkdsk to make sure that everything is fixed.

After 3 evenings and plenty of swear words, it's a great success! smile

Final words

There are two kinds of people, those who back up their stuff and those who have never lost all their data. Be smart and make sure you have proper backups! Otherwise, be prepared to spend few evenings learning Linux disk management tools and cursing their command-lines.

Till next time!

16 Feb

NetBalancer: should you trust it?

Last few months people kept bashing antivirus and security software in general. Like on Twitter or their personal pages. Sure, Twitter is full of opinionated idiots who just love to complain about everything that doesn't match their point of view. On a few occasions they are right and even I have written about some of the issues with antiviruses before.

But!

But you'd be f*king stupid to delete your antivirus just because it has some bugs. Doorlocks get picked by criminals every day and people still use them. Professional lockpickers do exist - it's their job to break lock's security mechanism and get you back in the house when you lose your keys. Tavis Ormandy is a professional lockpicker - only he works in the digital world. It's his job to break digital security mechanisms and help vendors to fix the issues.

Having said that, not all software is created equal. Sometimes new and dangerous features get added to an otherwise great software. These features look good on paper but they can really ruin someone's day. Today, I'll demonstrate one such feature.

Introducing SeriousBit NetBalancer

NetBalancer is a Windows application for local network traffic control and monitoring. It shows you the network traffic on your computer and helps you to set limits, priorities and rules for that traffic. Some sort of a firewall - but better. It can prioritize your traffic, schedule it for specific times, do statistics, make graphs and charts and what not. And it looks really good!

Predefined Priorities

NetBalancer's Predefined Priorities is a feature that looks great on paper.

For those of you who are not sure what priorities are best for your PC we decided in NetBalancer 8.5 to add some predefined priorities.
These priorities include the most used programs and processes, currently about 1700 total (and counting), and are set to match the needs of most users

It could be used for virtually everything:

  • giving high priority to VoIP applications and games
  • making sure background processes (eg. software updaters) don't interrupt your Youtube experience
  • and even blocking malware

The possibilities are endless. In fact, virtually all of the antivirus products use similar databases to preconfigure their firewalls. It makes total sense after all!

However, the devil is in the details. All such databases must be maintained. New version of Skype comes out, you need to update database. League of Legends releases new update, you must update the database. And you must do it very fast, so that your users don't suffer from misbehaved firewall. It's a lot of work.

Since NetBalancer is made by a small company called SeriousBit SRL, I was naturally curious how they manage to do that. smile

Inside Predefined Priorities

First, I needed to obtain the complete database of the priorities. You could try to find something in C:\ProgramData\SeriousBit\NetBalancer\ but it would be more interesting to find and download correct files for the official servers, right? smile After a quick string search, I learned that priorities can be downloaded from https://netbalancer.com/api/internal/predefinedpriorities. It's a huge JSON file but isn't encrypted or signed in any way.

That's a serious red flag right there. Security companies vigorously protect their databases - it's their know-how, their crown jewels. And they use digital signatures to make sure that the databases aren't tampered with. After all, which developer wants to see his product in news like "MalwareBytes: multiple security issues"? smile

OK, in this case JSON file is downloaded over HTTPS, therefore it's slightly harder to intercept traffic and modify it. So, let's ignore this issue for a moment and look at the JSON data instead.

In a minute or two, I was in the full "WTF?" mode.

Here's an excerpt from the JSON, prettified for easier viewing:

Setting high priority for RAR and TMP files.. More than 2000 entries like that? WTF?

How about this?

Yes, I want to download my porn with a high priority, thank you very much!

But how on earth that got through the QA process? Is there any QA process in SeriousBit SRL? I highly doubt that..

Unsolicited user data gathering

All those entries made me think - how is it possible that NetBalancer's database contains such crap information? Most obvious answer was - it's submitted by users. To verify the guess, I took a sneak peek inside SeriousBit.NetBalancer.Core.dll. And there it was:

The call is coming from here:

There you have it - if you have enabled "Predefined Priorities", NetBalancer will also silently upload all your priorities to their servers.

Want to wreak some havoc with unsuspecting users of NetBalancer? Post your own JSON file that blocks all traffic for all the browsers - apparently NetBalancer doesn't validate user submissions and will happily distribute them to other users. bigsmile

Abusing existing database

I was also wondering what is the meaning of ExeNameCrc field. smile Turns out that NetBalancer uses CRC32 of filename as a key in the dictionary that manages process priorities To make matters easier, they also supply you with a proper filename in ExecutablePath field. So, if you want to make sure your malware has unlimited traffic and high download priority, just name it swarm.exe:

Indeed, CRC32("swarm.exe") = 1475648703, as you can verify in some online CRC32 calculator..

A quick test confirms that too:

Conclusion

Trust is a delicate subject. On the one hand, all the Cloud and Connected things make your life much easier. On the other hand, you must choose wisely who you trust and what data he/she can access. I doubt that SeriousBit intentionally created such buggy and dangerous feature in NetBalancer. But that doesn't mean I would ever want it to be running on my machine!

Have fun and stay safe!

06 Feb

Updated Molebox unpacker

During last year, the most common complaint on this blog was "your Molebox unpacker cannot unpack this crazy big EXE of MMORPG game X, Y or Z."

Sounds like an easy problem to fix, right? Well, that's not true - but I finally did it!

TL;DR - new version of unpacker is here: https://www.mediafire.com/?t3xw46s554it5fp

In the rest of the post I'll describe the obstacles I had to overcome while solving this seemingly simple problem.

Delphi TMemoryStream limitation

First, unpacker is written using classic (non-.NET) Delphi and compiled as x86 executable. And standard Delphi streams are retarded. TMemoryStream uses GetMem - which ends up somewhere in Delphi memory manager and VirtualAlloc. That doesn't work well with 800+MB files.

I ended up with implementing custom stream backed by temporary file (CreateFile with FILE_ATTRIBUTE_TEMPORARY | FILE_FLAG_DELETE_ON_CLOSE).

Pointer magic

Since the original unpacker was using TMemoryStream, the whole file was loaded in memory as a continuous memory block and I could easily read/write each byte of file using pointers. Something like this:

Guess what? Files don't work that way.. sad I had to do a full and complete rewrite of all those methods.

Zlib conflicts

Original unpacker was compiled with Delphi 3. Delphi 3 didn't have Zlib library, so you had to supply your own Zlib implementation. But it won't compile with new versions of Delphi, giving error message

Unit Graphutil was compiled with a different version of zlib.TZDecompressionStream.

The solution was to get rid of my Zlib implementation and rewrite all methods that deal with decompression.

ANSI strings

In Delphi 3 all strings were ANSI. Starting from Delphi 2007, strings are Unicode. Since Molebox internally uses ANSI, it required changing quite a few structure definitions and rewriting several string manipulation routines. It's a lot of fun (and source of the most obscure bugs), trust me!

Conclusion

I hope you find this unpacker useful. But if it doesn't work for you, please send me an error report with all the details you can and I'll try to fix it. Have fun!

Download link: https://www.mediafire.com/?t3xw46s554it5fp

01 Feb

Moving to a new host

Last week MaxXor suggested that I should add HTTPS support to my blog. My existing free host (bplaced) doesn't offer HTTPS, so I decided to finally switch to paid hosting. After thinking a bit, reading customer references, I chose Active24 - and so far the experience has been overwhelmingly positive.

  • Webhost was set up within minutes, including self-signed HTTPS certificate;
  • As soon as you update your DNS entries, Let's Encrypt certificate is issued automatically. You don't need to do anything yourself!
  • Unlimited disk space;
  • Unlimited traffic;
  • Unlimited cron jobs;
  • And everything "just works™";

For now HTTPS is optional (try https://lifeinhex.com/), I'll start enforcing HTTPS in a few days after fixing all the mixed-content warnings. smile

Have fun and stay safe (and let me know if you notice any issues)!

26 Jan

Abusing Microsoft-signed executables

This morning I noticed an article from Cylance named "Graftor Variant Leveraging Signed Microsoft Executable". It's a nice article, so I can really recommend you read it.

TL;DR version: Graftor authors are using DLL hijacking in SrcTool.exe to load their own dbghelp.dll. If antimalware solution trusts executable that's signed by Microsoft (most of them do!) and doesn't check all the DLLs it loads, malicious code will not be detected.

Other vulnerable files

I decided to look for other Microsoft-signed files that could be abused in a similar manner. One quick search for EXE files in folder C:\Program Files (x86)\Windows Kits that also contain string dbghelp.dll and here's the result:

  • agestore.exe
  • cdb.exe
  • dbh.exe
  • kd.exe
  • mftrace.exe
  • ntkd.exe
  • ntsd.exe
  • srctool.exe
  • symchk.exe*
  • symstore.exe
  • tlist.exe
  • tracefmt.exe
  • tracepdb.exe

*symchk.exe also requires SymbolCheck.dll.

All these files are statically linked to dbghelp.dll and therefore vulnerable to DLL hijacking. agestore.exe, mftrace.exe, srctool.exe, symstore.exe, tlist.exe, tracefmt.exe and tracepdb.exe are the best targets - if you don't pass any command-line to them, they load dbghelp.dll but don't call any of its APIs and therefore will not crash.

Demo time

Here's a small fake dbghelp.dll you can use for testing: https://www.mediafire.com/?yx677bhxtyc13pu

Place it in the folder with vulnerable EXE lies and run the EXE. If a "DLL Hijacking" messagebox shows up, the EXE is vulnerable. smile Something like this:

Have fun and keep it safe!