PELoader

PELoader implement various shellcode injection techniques, and use libpeconv library to load encrypted PE files instead of injecting shellcode into remote thread.

Following techniques were implemented:

• Module Stomping (LoadLibrary)
• Module Stomping (NtMapViewOfSection)
• Transacted Hollowing
• Ghostly Hollowing
• NtMapViewOfSection (RWX-RW-RX)
• NtAllocateVirtualMemory (RW-RX)

Credits: most of my work was based on @hasherezade's PoC scripts.

Testing

PELoader was tested on Windows 10 with Cortex XDR / SentinalOne / Windows Defender / CrowdStrike, and Windows Defender / CrowdStrike detected Transacted Hollowing techniques. Characteristics of each techniques were tested with a memory scanner tool Moneta from @forrest-orr.

Module Stomping (LoadLibrary)

Call LoadLibrary to load a legitimate DLL. Overwrite DLL with payload

Pros

• payload mapped as MEM_IMAGE which looks legitimate for EXE or DLL
• impersonating a legitimate DLL
• Sections mapped with original access rights (no RWX)

Module Stomping (NtMapViewOfSection)

Call NtCreateSection to create file mapping object (PAGE_READONLY) for a legitimate DLL, and call NtMapViewOfSection to map it to current process. Overwrite the DLL with payload.

Pros

• payload mapped as MEM_IMAGE which looks legitimate for EXE or DLL
• impersonating a legitimate DLL
• Sections mapped with original access rights (no RWX)
• Not connected to the list of modules (invisible for Module32First/Module32Next)

Cons

• Not connected to the list of modules (check "Missing PEB module" in bellow Moneta's scanning result)

reference to @hasherezade's PoC.

Transacted Hollowing

A hybrid between Process Hollowing and Process Doppelgänging. Create “invisible” file within the NTFS transaction and write payload into the file. Map section to current process and execute it.

Pros

• Payload mapped as MEM_IMAGE
• Sections mapped with original access rights (no RWX)
• dummy file not necessary to be exist

Cons

• Detection if there is TxF activity monitoring

Ghostly Hollowing

A hybrid between Process Hollowing and Process Ghosting. Create a file with delete pending state and write payload into the file. Map section to current process and execute it.

Pros

• Payload mapped as MEM_IMAGE
• Sections mapped with original access rights (no RWX)
• Avoid “System Idle Process” without any image path (IOC of process ghosting)

Cron

• Dummy file created on disk

reference to @hasherezade's PoC.

NtMapViewOfSection (RWX-RW-RX)

Call NtCreateSection to create memory section (RWX). Call NtMapViewOfSection map a view to current process (RWX). Call VirtualProtect to change protection to RW. Copy shellcode to mapped section. Change protection to RX and execute it.

Pros

• Payload mapped as MEM_MAPPED to avoid MEM_PRIVATE which is common in malware

Cons

• Set memory page to RWX protection at initial stage
• abnormal mapped EXE memory with RX protection

NtAllocateVirtualMemory (RW-RX)

Call NtAllocateVirtualMemory to allocate memory (RW). Copy shellcode to memory. Change protection to RX and execute it.

Pros

• avoid RWX memory page

Cons

• staging shellcode to memory page with private type MEM_PRIVATE
• abnormal private EXE memory with RX protection

Usage

AES Encrypt Payload

Convert PE file to shellcode with pe_to_shellcode and encrypted with PELoader

cmd> .\pe2shc.exe mimikatz.exe
Reading module from: mimikatz.exe
[WARNING] This is a console application! The recommended subsystem is GUI.
[+] Saved as: mimikatz.shc.exe
cmd> set hagrid=enc mimikatz.shc.exe
cmd> .\PELoader.exe
argument: enc mimikatz.shc.exe
Encrypting File

PE Execution

Set argument to environment variable "hagrid" and execute PELoader

cmd> set hagrid=cdll mimikatz.shc.exe.enc
cmd> .\PELoader.exe  version
argument: cdll mimikatz.shc.exe.enc
Classic DLL Hollowing
[*] target dll: C:\WINDOWS\system32\aadtb.dll
[*] implant dll: mimikatz.shc.exe.enc
[*] Loading the DLL (using LoadLibary, classic DLL hollowing)...
[*] Overwriting the mapping
[*] Module Overloading finished...
[*] Executing Implant's Entry Point: 7ff8cf9d7578
[*] Executing Implant as EXE

  .#####.   mimikatz 2.2.0 (x64) #19041 Aug 10 2021 17:19:53
 .## ^ ##.  "A La Vie, A L'Amour" - (oe.eo)
 ## / \ ##  /*** Benjamin DELPY `gentilkiwi` ( [email protected] )
 ## \ / ##       > https://blog.gentilkiwi.com/mimikatz
 '## v ##'       Vincent LE TOUX             ( [email protected] )
  '#####'        > https://pingcastle.com / https://mysmartlogon.com ***/

mimikatz(commandline) # version

mimikatz 2.2.0 (arch x64)
Windows NT 10.0 build 19043 (arch x64)
msvc 150030729 207

mimikatz #

Improvement

• @forrest-orr made a detailed comparison on variations of shellcode implant in this article
• @dglenx moved the concept to remote process injection and suggest a couple of ways to address IOCs in this article

References

• https://github.com/hasherezade/libpeconv
• https://github.com/hasherezade/module_overloading
• https://github.com/hasherezade/transacted_hollowing
• https://www.forrest-orr.net/post/masking-malicious-memory-artifacts-part-iii-bypassing-defensive-scanners
• https://www.secforce.com/blog/dll-hollowing-a-deep-dive-into-a-stealthier-memory-allocation-variant/