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https://github.com/aguinet/wannakey

Wannacry in-memory key recovery
https://github.com/aguinet/wannakey

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Wannacry in-memory key recovery

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README 

        
Wannakey

========



WARNING

=======



This software has only been tested and known to work under Windows XP, 7 x86,

2003, Vista and Windows Server 2008 (tests by @msuiche).



Please also note that you need some luck for this to work (see below), and so

it might not work in every case!



DISCLAMER

=========



- This code is and will always be GPLv3. See LICENSE file attached.



Updates

=======



v2.1

----



* optimization of the prime search process (see https://github.com/aguinet/wannakey/issues/2).

* OpenMP version that uses as many core as available to speed-up the process

* tool that finds whether wannakey's technique has chances to work on a running Windows OS



v2.0

----



* automatically find the encryption process PID

* write the private key so that the original malware's process can decrypt the files (using the Decrypt button)

* code refactoring and cmake usage



v0.2

----



* The generated private RSA key had invalid computed fields, which made the key

  not importable with CryptImportKey under Windows XP (fixed). wanafork and/or wanadecrypt can

  now be used directly from XP.



* Updated the binary with this fix and a static build (no need for the MSVC

  runtime anymore)



v0.1

----



* Original version



Introduction

============



This software allows to recover the prime numbers of the RSA private key that are used by Wanacry.



It does so by searching for them in the ``wcry.exe`` process. This is the

process that generates the RSA private key. The main issue is that the

``CryptDestroyKey`` and ``CryptReleaseContext`` does not erase the prime

numbers from memory before freeing the associated memory.



This is not really a mistake from the ransomware authors, as they properly use

the Windows Crypto API. Indeed, for what I've tested, under Windows 10,

``CryptReleaseContext`` does cleanup the memory (and so this recovery technique

won't work). It can work under Windows XP because, in this version,

``CryptReleaseContext`` does not do the cleanup. Moreover, MSDN states this,

for this function : "After this function is called, the released CSP handle is

no longer valid. This function does not destroy key containers or key pairs.".

So, it seems that there are no clean and cross-platform ways under Windows to

clean this memory.



If you are lucky (that is the associated memory hasn't been reallocated and

erased), these prime numbers might still be in memory.



That's what this software tries to achieve.



Usage

=====



You can use the binary ``wannakey.exe`` in the bin/ folder. It will locate the

encryption PID by itself. If it can't, you might need to search it by hand and

pass it as an argument of the ``wannakey.exe`` tool.



If you have multiple cores, you can use the ``wannakey_omp.exe`` binary. If you

don't have the ``vcomp140.dll`` on your system, you can copy alongside

``wannakey_omp.exe`` the version that is present in the ``bin`` directory

(extracted from the MSVC 2015 C++ runtime). Unfortunately, it doesn't seem

straightforward to statically link with this library. 



If the key had been succeesfully generated, you will just need to use the

"Decrypt" button of the malware to decrypt your files!



Windows Crytp API leak check

============================



A tool named "winapi_check" (see the bin/ directory) checks whether the Windows

Crypto API remove the private key's primes from memory or not. This allows to

verify if wannakey has a small chance or not to work.



Please note that, even if this tool says wannakey stands a chance, it doesn't mean

it will work!



If you have tried this tool, please report the results here: https://github.com/aguinet/wannakey/issues/5.



Compile from source

===================



You need at least Visual Studio 2015 express and CMake.



Launch a VS2015 Native Tools command line prompt and run:



.. code::



  > cd /path/to/wannakey/wannakey/

  > mkdir build

  > cd build

  > cmake -G "Visual Studio 14 2015" -T "v140_xp" ..

  > cmake --build . --config "release"



Binary will be in the src/Release directory.



Credits

=======



* @wiskitki who spotted the ``CryptReleaseContext`` issue with Windows 10 (which actually wipe the primes in memory).

* @hackerfantastic for releasing the sample I used

* Miasm (https://github.com/cea-sec/miasm) for its help extracting the DLL and reversing the whole thing

* Wine sources for the Windows RSA private key format.