Full Report
Adversaries frequently repurpose trusted tools like curl.exe to tunnel traffic through SOCKS proxies and even reach .onion domains. Whether it’s for data exfiltration or command-and-control communication, such activity often flies under the radar—unless you’re explicitly detecting for it. This is exactly what CrowdStrike Endpoint Security Query Language allows teams to do. But when logic grows […] The post Visualizing Malicious curl Proxy Activity in CrowdStrike with Uncoder AI appeared first on SOC Prime.
Analysis Summary
# Tool/Technique: curl.exe Abuse with TOR Proxy Activity
## Overview
This summary focuses on the detection and visualization of malicious activity involving the legitimate `curl.exe` utility being used in conjunction with a TOR proxy, often indicative of post-exploitation or C2 communication attempting to leverage anonymization layers. The context highlights the use of the Uncoder AI tool to bring transparency to complex detection logic (like CrowdStrike regex) targeting this specific behavior.
## Technical Details
- Type: Technique (Abuse of legitimate tool)
- Platform: Windows (implied by CrowdStrike context, targeting `curl.exe`)
- Capabilities: Establishing network connections, potentially to attacker-controlled infrastructure (like TOR hidden services) while masking the source IP.
- First Seen: Not explicitly mentioned, but associated with evolving threat actor TTPs.
## MITRE ATT&CK Mapping
This activity primarily aligns with Command and Control mechanisms:
- TA0011 - Command and Control
- T1071 - Application Layer Protocol
- T1071.001 - Web Protocols (if using HTTP/S over curl)
- T1090 - Proxy
- T1090.003 - Multi-hop Proxy (TOR inherently functions as one)
## Functionality
### Core Capabilities
- Utilizing `curl.exe` to make network requests.
- Using an anonymizing proxy system (specifically mentioning TOR, implying `.onion` usage or traffic routing through TOR exit nodes).
- Blending post-exploitation traffic with legitimate administrative or system tool usage.
### Advanced Features
- Bypassing perimeter defenses through anonymized traffic routing (TOR).
- Potentially interacting with hidden services (.onion domains) for secure C2 communication.
- Evading straightforward network inspection by leveraging a trusted binary (`curl.exe`).
## Indicators of Compromise
- File Hashes: N/A (Focus is on process execution, not a unique malware hash)
- File Names: `curl.exe`
- Registry Keys: N/A
- Network Indicators: Traffic directed toward or characteristic of TOR usage, including connections to domains ending in `.onion`.
- Behavioral Indicators: Execution of `curl.exe` exhibiting command line arguments associated with proxy configuration or accessing known TOR destinations.
## Associated Threat Actors
- Threat actors utilizing techniques to obscure C2 communication, specifically mentioning potential use by backdoors like **Kalambur** or other implants.
## Detection Methods
- Detection relies on complex logic (e.g., CrowdStrike regex) combining:
1. Process match (`curl.exe`).
2. Detection of proxy usage parameters.
3. Identification of `.onion` domain references in the command.
- **Visualization/Triage**: Tools like Uncoder AI help to visually interpret these complex, nested detection rules for faster triage and validation.
## Mitigation Strategies
- Monitor for unusual command-line arguments accompanying `curl.exe` execution.
- Implement network segmentation and egress filtering to restrict unauthorized external connections.
- Block or monitor traffic destined for known TOR infrastructure or exit nodes if not organizationally required.
- Tune detection rules to specifically look for the combination of `curl.exe`, proxy flags, and anonymous domains.
## Related Tools/Techniques
- Abuse of other legitimate system binaries for C2 (e.g., PowerShell, BITSAdmin, Certutil).
- Use of other anonymizing tools or proxies.
- Malware families relying on built-in operating system tools rather than custom executables (Living Off The Land - LOLBins).
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*Note: Specific technical IOCs like hashes or exact C2 domains were not provided in the context; the focus was on the analytic technique and the tooling used for detection engineering.*