hunting-for-webshell-activity

name	hunting-for-webshell-activity
description	Hunt for web shell deployments on internet-facing servers by analyzing file creation in web directories, suspicious process spawning from web servers, and anomalous HTTP patterns.
domain	cybersecurity
subdomain	threat-hunting
tags	["threat-hunting","mitre-attack","webshell","persistence","web-server","t1505","proactive-detection"]
version	1.0
author	mahipal
license	Apache-2.0
d3fend_techniques	["Executable Denylisting","Execution Isolation","File Metadata Consistency Validation","Restore Access","Process Termination"]
nist_csf	["DE.CM-01","DE.AE-02","DE.AE-07","ID.RA-05"]

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

Detection Gaps & Validation

• File-create hunting misses a lot: shells appended to existing legit .aspx/.php, stored in a database, loaded as an in-memory IIS module (T1505.004), or served via handler mapping under a benign extension. Hash/signature scans miss obfuscated one-liners like <?php @eval($_POST['x']);?>.
• Process lineage is the durable signal: w3wp.exe / httpd / tomcat / php-cgi spawning cmd.exe/powershell/whoami (EID 1, ParentImage = web server) catches even unknown shells; EID 11 FileCreate in webroot by the web-server process (not a deploy pipeline) is high-signal.
• Low-and-slow operators: China Chopper uses tiny intermittent POSTs that hide in netflow — needs web/proxy log content inspection, not volume thresholds.
• Validate: drop a benign test .aspx that runs whoami; confirm the w3wp→cmd EID 1 chain and the EID 11 write both fire.
• FP tuning: baseline legitimate CI/CD deploys and admin maintenance scripts that legitimately write to webroot.

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.