Borrowing it
Nothing to install: this file belongs to mtnyilmaz/agents. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/mtnyilmaz/agents/main/.agents/skills/sast-ssti/SKILL.mdgit clone --depth 1 https://github.com/mtnyilmaz/agentsWrote 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.
[](https://agentmods.dev/skills/mtnyilmaz/agents/sast-ssti)<a href="https://agentmods.dev/skills/mtnyilmaz/agents/sast-ssti"><img src="https://agentmods.dev/badge/skills/mtnyilmaz/agents/sast-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.
<a href="https://agentmods.dev/skills/mtnyilmaz/agents/sast-ssti"><img src="https://agentmods.dev/badge/skills/mtnyilmaz/agents/sast-ssti.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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 | $0.00097 | $0.06760 |
| Opus 5 | $0.00048 | $0.03380 |
| Sonnet 5 | $0.00019 | $0.01352 |
| Haiku 4.5 | $0.00010 | $0.00676 |
Grade A, and why
sast-ssti scanned grade A with 2 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 9d 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.
Unrestricted tool accesslowExcessive agency
A wildcard tool grant or "run any command" leaves no least-privilege boundary at all.
- **Sandboxed template engines configured with a restricted environment**: Liquid, Mustache, and similar logic-less engines cannot execute arbitrary code even if the template string comes from user input — but still flag Downgraded: this mod is about security review, or the phrase is quoted, so it is likely naming the pattern rather than instructing it.
Runs shell commandslowCapability
Expected in a hook, worth knowing in a rule or an instructions file.
// Payload: ?template=<%- global.process.mainModule.require('child_process').execSync('id') %> This is a copy
86% identical to sast-ssti — 99 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
How it starts
The opening of the file, as written. The whole thing — 558 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Server-Side Template Injection (SSTI) Detection
You are performing a focused security assessment to find Server-Side Template Injection vulnerabilities in a codebase. This skill uses a two-phase approach with subagents: recon (find all places where templates are rendered from dynamic strings) then taint (confirm whether user-supplied input reaches those rendering sites as the template string).
Prerequisites: sast/architecture.md must exist. Run the analysis skill first if it doesn't.
What is SSTI
Server-Side Template Injection occurs when user-supplied input is embedded directly into a template string that is then evaluated by a template engine. Unlike passing user data as context variables to a static template, SSTI means the user can write template syntax that the engine will execute — leading to arbitrary code execution, file read, or full server compromise.
The core pattern: unvalidated user input is used as the template string passed to a template engine's render/compile/evaluate function.
What SSTI IS
- Passing user input as the template string to be compiled or rendered:
Template(user_input).render()— Jinja2env.from_string(user_input).render()— Jinja2render_template_string(user_input)— Flaskejs.render(user_input, ctx)— EJS (Node.js)nunjucks.renderString(user_input, ctx)— NunjucksHandlebars.compile(user_input)(ctx)— Handlebarspug.render(user_input, ctx)— Pug/Jade_.template(user_input)(ctx)— Lodash/UnderscoreVelocity.evaluate(ctx, user_input)— Apache Velocity (Java)new Template("anon", new StringReader(user_input), cfg).process(...)— FreeMarker (Java)new ST(user_input).render()— StringTemplate4 (Java)thymeleafEngine.process(user_input, ctx)— Thymeleaf (Java)\Twig\Environment::createTemplate(user_input)->render(ctx)— Twig (PHP)$smarty->fetch("string:" . user_input)— Smarty (PHP)Liquid::Template.parse(user_input).render(ctx)— Liquid (Ruby)ERB.new(user_input).result(binding)— ERB (Ruby)t, _ := template.New("x").Parse(user_input); t.Execute(w, data)— Gotext/templateTemplate.fromString(user_input).render(ctx)— Pebble (Java)
What ships with it
1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 9d ago First seen · 558 lines · 97 tokens per session scan A 86e2aee397d1
sast-ssti is a skill published in the GitHub repository mtnyilmaz/agents (6 stars, last pushed 3mo ago), licensed MIT. It adds 97 tokens to every session and 6,760 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it A with 2 findings (unrestricted tool access, runs shell commands). It is 86% identical to sast-ssti, differing in 99 lines, and is treated as a copy.
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