Full Report
ESET assess the differences between CryptoFortress and TorrentLocker: two very different strains of ransomware.
Analysis Summary
# Tool/Technique: CryptoFortress (vs. TorrentLocker)
## Overview
CryptoFortress is a strain of ransomware that explicitly mimics the appearance (ransom message and payment page HTML/CSS) of the previously known ransomware, TorrentLocker. However, technical analysis reveals that CryptoFortress is structurally and functionally a different piece of malware than TorrentLocker.
## Technical Details
- Type: Malware family (Ransomware)
- Platform: Windows (Inferred, based on typical ransomware targets and associated file signatures)
- Capabilities: Encrypting user files on the compromised system and demanding Bitcoin for decryption.
- First Seen: March 2015 (Context of the article)
## MITRE ATT&CK Mapping
*Note: Specific initial access and execution methods are mentioned (Nuclear Pack exploit kit, Spam), but the core malware functions map below.*
- **TA0011 - Command and Control**
- T1071 - Application Layer Protocol
- **TA0003 - Persistence** (Implied, as ransomware executes)
- **TA0001 - Initial Access**
- T1190 - Exploit Public-Facing Application (via Nuclear Pack)
- **TA0040 - Impact**
- T1486 - Data Encrypted for Impact
## Functionality
### Core Capabilities
The primary function is file encryption coupled with presentation similarity to TorrentLocker to increase victim cooperation.
### Advanced Features
- **Encryption Algorithm Difference:** Uses AES-256 ECB, whereas TorrentLocker used AES-256 CBC.
- **Ransom Key Management:** Uses RSA-1024 for AES key encryption.
- **Cryptographic Library:** CryptoFortress utilizes the **Microsoft CryptoAPI**, unlike TorrentLocker, which used LibTomCrypt.
- **File Encryption Scope:** Encrypts the **first 50% of the file (up to 5 MB)**, versus TorrentLocker's encryption of the first 2 MB.
- **C2 Communication:** Does **not** have a hardcoded C&C server, relying on fetching resources from C&C.
- **Ransom Page Location:** The ransom page is **included in the malware**, whereas TorrentLocker fetched it from the C&C server.
## Indicators of Compromise
- File Hashes:
- SHA-1: `7085e1d96c34d6d1e3119202ab7edc95fd6f304`
- File Names: Not specified, but identified by ESET detection name.
- Registry Keys: Not specified.
- Network Indicators: C&C servers/domains are dynamically fetched or referenced, not explicitly hardcoded and listed in the summary scope.
- Behavioral Indicators: Detection name `Win32/Kryptik.DAPB`.
## Associated Threat Actors
- Threat actors are not explicitly named, but the malware has been observed being distributed by the **Nuclear Pack exploit kit**.
## Detection Methods
- Signature-based detection: ESET Detection named `Win32/Kryptik.DAPB`.
- Behavioral detection: Analyzing deviations from expected file I/O (encrypting large portions of files).
## Mitigation Strategies
- **Patching/Vulnerability Management:** Addressing vulnerabilities exploited by delivery mechanisms like the Nuclear Pack exploit kit.
- **Backup Strategy:** Ensuring robust, offline backups to recover from file encryption impact.
- **Host-based protection:** Using EDR/AV solutions capable of identifying known malware hashes and heuristic detection for crypto-malware activity.
## Related Tools/Techniques
- **TorrentLocker:** The ransomware whose interface and communication strategy CryptoFortress directly mimics.
- **Nuclear Pack:** The exploit kit observed distributing CryptoFortress samples.