Full Report
When attackers repurpose legitimate binaries like curl.exe to tunnel through SOCKS proxies and access .onion domains, it poses a major visibility gap for defenders. These behaviors can signal C2 activity, data staging, or use of a backdoor like Kalambur. VMware Carbon Black allows you to detect these patterns with detailed command-line monitoring, but parsing the […] The post Detecting Covert curl Usage with Uncoder AI’s Decision Tree in Carbon Black appeared first on SOC Prime.
Analysis Summary
# Tool/Technique: Covert `curl` Usage Detection via Uncoder AI and Carbon Black Telemetry
## Overview
This summary details the process and findings related to detecting covert instances of the legitimate utility `curl` being used by malicious actors, specifically when combined with proxy tunnels and attempts to reach `.onion` (Tor network) addresses. The detection strategy utilizes Carbon Black telemetry analyzed through Uncoder AI's decision tree logic to turn raw query data into transparent, understandable security rules.
## Technical Details
- Type: Technique (Detection Methodology leveraging a legitimate tool)
- Platform: Windows (Implied by Carbon Black telemetry usage, targeting endpoint processes)
- Capabilities: Translating complex threat telemetry into interpretable decision trees for enhanced threat hunting and rule creation. Focuses on detecting abuse of native tools for low-noise exfiltration/C2.
- First Seen: May 02, 2025 (Date of the article)
## MITRE ATT&CK Mapping
The general activity described aligns with the use of legitimate system tools for command and control or data staging.
- **TA0011 - Command and Control**
- T1071 - Application Layer Protocol
- **TA0005 - Defense Evasion**
- T1218 - Signed Binary Proxy Execution
- T1218.011 - Signed Binary Proxy Execution: Regsvr32 (Not directly applicable, listed as a general defense evasion alignment for proxy techniques)
- *Note: Using `curl` to communicate over non-standard protocols or proxies often falls here or under standard C2 techniques.*
- **TA0010 - Exfiltration**
- T1048 - Exfiltration Over Alternative Protocol (If data is tunneled)
## Functionality
### Core Capabilities
- Detection of `curl` command-line usage that suggests malicious redirection (e.g., proxy tunnels).
- Identification of connections targeting Tor infrastructure (`.onion` addresses), indicating high-evasion communication channels.
- Conversion of security logic (input query) into an AI-generated Decision Tree for visual inspection, sharing, and validation.
### Advanced Features
- **Low-Noise TTP Monitoring**: Focuses on techniques that evade simple signature detection by blending in with normal system administration activity using native utilities (`curl`).
- **Detection Engineering Acceleration**: Uncoder AI provides a fast path from raw detection query logic to a verifiable, understandable security artifact (decision tree).
## Indicators of Compromise
The article focuses on the *methodology* of detection rather than providing specific, static IOCs. The detection focuses on behavior:
- File Hashes: N/A (Focuses on command line/behavior)
- File Names: `curl` (Targeted binary)
- Registry Keys: N/A
- Network Indicators: Connections targeting domains ending in `.onion` (Defanged: `[.]onion`) via proxy configurations.
- Behavioral Indicators: Execution of `curl` with parameters indicating proxy chaining (tunneling) or direct connection attempts to anonymity networks.
## Associated Threat Actors
Threat actors utilizing malware that leverages native tools (like `curl`) for low-noise C2 or exfiltration attempts. Explicit threat actor names are not mentioned, but the focus is on actors employing **low-noise, high-evasion TTPs**.
## Detection Methods
- **Behavioral Detection**: Monitoring command-line arguments and process relationships associated with `curl` execution in Carbon Black.
- **AI-Assisted Logic Review**: Use of Uncoder AI to translate complex logic derived from threat intelligence (or initial forensic analysis) into a clear, actionable decision tree structure.
## Mitigation Strategies
- **Application Control**: Restrict the execution or modification of utilities like `curl` in high-security environments if they are not required for standard operations.
- **Network Filtering**: Implement egress filtering to potentially block known unstable/unverified Tor exit nodes, although this is challenging given the nature of `.onion` services.
- **Enhanced EDR Policy**: Configure EDR (Carbon Black) solutions to heavily log and alert on unusual parameters passed to native tools like `curl`, especially when involving proxy or network redirection flags.
## Related Tools/Techniques
- **Tools**: Carbon Black (Telemetery source), Uncoder AI (Detection engineering/logic visualization tool).
- **Techniques**: Living Off The Land Binaries (LOLBins) usage, Traffic Obfuscation/Tunneling.