Anthropic-Cybersecurity-Skills/skills/hunting-for-webshell-activity/SKILL.md

name, description, domain, subdomain, tags, version, author, license, d3fend_techniques, nist_csf, mitre_attack

name	description	domain	subdomain	tags	version	author	license	d3fend_techniques	nist_csf	mitre_attack
hunting-for-webshell-activity	Runs a hypothesis-driven threat hunt for web shell deployment (T1505.003) on internet-facing servers by analyzing file creation in web directories, suspicious child-process spawning from web server processes, and anomalous HTTP request patterns. Use when hunting for web shells after a public-facing app compromise, when EDR/SIEM alerts fire on webserver process anomalies, or during incident response on internet-facing infrastructure.	cybersecurity	threat-hunting	threat-hunting mitre-attack webshell persistence web-server t1505 proactive-detection	1.0	mahipal	Apache-2.0	Executable Denylisting Execution Isolation File Metadata Consistency Validation Restore Access Process Termination	DE.CM-01 DE.AE-02 DE.AE-07 ID.RA-05	T1046 T1057 T1082 T1083 T1547

Hunting For Webshell Activity

When to Use

• When proactively hunting for indicators of hunting for webshell activity in the environment
• After threat intelligence indicates active campaigns using these techniques
• During incident response to scope compromise related to these techniques
• When EDR or SIEM alerts trigger on related indicators
• During periodic security assessments and purple team exercises

Prerequisites

• EDR platform with process and network telemetry (CrowdStrike, MDE, SentinelOne)
• SIEM with relevant log data ingested (Splunk, Elastic, Sentinel)
• Sysmon deployed with comprehensive configuration
• Windows Security Event Log forwarding enabled
• Threat intelligence feeds for IOC correlation

Workflow

1. Formulate Hypothesis: Define a testable hypothesis based on threat intelligence or ATT&CK gap analysis.
2. Identify Data Sources: Determine which logs and telemetry are needed to validate or refute the hypothesis.
3. Execute Queries: Run detection queries against SIEM and EDR platforms to collect relevant events.
4. Analyze Results: Examine query results for anomalies, correlating across multiple data sources.
5. Validate Findings: Distinguish true positives from false positives through contextual analysis.
6. Correlate Activity: Link findings to broader attack chains and threat actor TTPs.
7. Document and Report: Record findings, update detection rules, and recommend response actions.

Key Concepts

Concept	Description
T1505.003	Web Shell
T1190	Exploit Public-Facing Application
T1059.001	PowerShell

Tools & Systems

Tool	Purpose
CrowdStrike Falcon	EDR telemetry and threat detection
Microsoft Defender for Endpoint	Advanced hunting with KQL
Splunk Enterprise	SIEM log analysis with SPL queries
Elastic Security	Detection rules and investigation timeline
Sysmon	Detailed Windows event monitoring
Velociraptor	Endpoint artifact collection and hunting
Sigma Rules	Cross-platform detection rule format

Common Scenarios

1. Scenario 1: China Chopper web shell via IIS vulnerability
2. Scenario 2: ASPXSpy through vulnerable upload
3. Scenario 3: PHP shell hidden in image file
4. Scenario 4: JSP shell via Tomcat manager console

Output Format

Hunt ID: TH-HUNTIN-[DATE]-[SEQ]
Technique: T1505.003
Host: [Hostname]
User: [Account context]
Evidence: [Log entries, process trees, network data]
Risk Level: [Critical/High/Medium/Low]
Confidence: [High/Medium/Low]
Recommended Action: [Containment, investigation, monitoring]