Full Report
Breakdown of a BumbleBee PowerShell Dropper & extracting the config of BumbleBee
Analysis Summary
# Tool/Technique: BumbleBee Loader (DocuSign Campaign)
## Overview
This summary details a cyber attack campaign impersonating DocuSign, utilizing a multi-layered execution chain involving phishing, archive files, LNK shortcuts, and a PowerShell loader script designed to deploy the BumbleBee malware loader.
## Technical Details
- Type: Malware family (BumbleBee Loader) / Loader technique (Powershell obfuscation)
- Platform: Windows (implied by LNK files and PowerShell usage)
- Capabilities: Initial access via phishing, file extraction/decryption, execution chaining, deployment of an intermediate loader (BumbleBee).
- First Seen: Campaign deployment evident around February 2023 (based on analysis date in script context).
## MITRE ATT&CK Mapping
This analysis primarily covers the initial stages of execution and defense evasion:
- **TA0002 - Execution**
- **T1204.002 - User Execution: Malicious File** (Tricking user into downloading/opening archive and LNK file)
- **T1059.001 - Command and Scripting Interpreter: PowerShell** (Use of the hidden `.ps1` script)
- **TA0005 - Defense Evasion**
- **T1027.001 - Obfuscated Files or Information: Compiled HTML File** (Although here used for distribution, the file structure is complex)
- **T1027 - Obfuscated Files or Information** (Base64 encoded strings modified to resemble `.gz` magic bytes)
## Functionality
### Core Capabilities
The initial infection chain focuses heavily on system bypassing and payload delivery:
1. **Phishing Lure:** Email claiming an invoice requires payment, providing a password (`RD4432`).
2. **Malicious Download:** A link hosted on OneDrive delivers an archive file (e.g., `.zip`).
3. **File Extraction:** The user must provide the password to extract an `.IMG` file.
4. **Shortcut Execution:** The `.IMG` file contains a visible `.LNK` file (`requested information`) which executes a **hidden `.ps1` script**.
5. **PowerShell Loader:** The script contains approximately 42 Base64 encoded strings (which are archives).
6. **De-obfuscation and Staging:** The script modifies the first character of the Base64 strings to simulate `.gz` magic bytes (`1f 8b`), decodes them, and saves them as `.gz` archives to load the next stage payload (implied to be the BumbleBee DLL).
### Advanced Features
- **Multi-Layered Obfuscation:** Uses Base64 encoding within a PowerShell script, combined with file format masquerading (modifying strings to mimic Gzip headers) to hide stages.
- **Hidden File Deployment:** Hiding the `.ps1` script inside an LNK file which is itself inside an `.IMG` file.
## Indicators of Compromise
- File Hashes:
- `requested_documents_714407544541.zip`: `d4a358c875ab55c811368eabe8fa33d09fe67f2d3beafa97b9504bf800a7a02d`
- `8702268950347.img`: `a55979165779c3c4fc1bc80b066837df206d9621b0162685ed1a6f6a5203d8af`
- `requested information.lnk`: `6fb690fbeb572f4f8f0810dd4d79cff1ca9dbd2caa051611e98d0047f3f2aa56`
- `documents.ps1`: `b6d05d8f7f1f946806cd70f18f8b6af1b033900cfaa4ab7b7361b19696be9259`
- Intermediate Stage (DLL): `2d5c9b33ed298f5fb67ce869c74b2f2ec9179a924780da65fcbc1a0e0463c5d0`
- BumbleBee Loader (BIN): `4a5d5e6537044cdbf8de9960d79c85b15997784ba1b74659dbfcb248ccc94f59`
- File Names: `requested_documents_714407544541.zip`, `requested information.lnk`
- Registry Keys: Not specified in the execution chain analysis.
- Network Indicators:
- Distribution host: `onedrive.live/download?cid=0F6CD861E2193F6E&resid=F6CD861E2193F6E%21118&authkey=ALbZV_c_Tn7O-OA` (Defanged: `onedrive[.]live`)
- Behavioral Indicators: Execution launched via LNK file pointing to a PowerShell script; creation of multiple `.gz` files from decoded strings.
## Associated Threat Actors
The **BumbleBee** malware is associated with initial access operations, sometimes preceding deployment of ransomware (like BlackCat/ALPHAV) or other significant backdoors (it has historical links to TrickBot operations).
## Detection Methods
- Signature-based detection: Known hashes of the sample chain files.
- Behavioral detection: Detection of LNK files executing PowerShell scripts with unusual, highly-encoded command line arguments. Monitoring for the specific string manipulation logic in the PowerShell script used to prepend 'H' to decoded strings.
- YARA rules: Specific rules could target the structure of the obfuscated PowerShell variables (`$elem{X}=...`).
## Mitigation Strategies
- **Email Security:** Implement strong filtering against suspicious attachments and social engineering tactics (e.g., fake invoice lures).
- **User Training:** Educate users to be highly skeptical of unsolicited attachments, external OneDrive links, and unsolicited requests for passwords.
- **Application Control:** Restrict or heavily scrutinize execution flows originating from archives, especially those that use LNK files to launch scripts.
- **PowerShell Security:** Enable PowerShell logging (Script Block Logging, Module Logging) to capture the deobfuscated script content during execution.
## Related Tools/Techniques
- **BumbleBee Loader:** The primary payload deployed; known to be a modular loader often used for subsequent stages like IcedID or Ransomware.
- **TrickBot Connection:** Mentioned in linked context regarding BumbleBee's history.
- **OneDrive/Cloud Hosting Abuse:** Usage of legitimate cloud services for hosting initial payloads.