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exploiting-template-injection-vulnerabilities

Detecting and exploiting Server-Side Template Injection (SSTI) vulnerabilities across Jinja2, Twig, Freemarker, and other template engines to achieve remote code execution.

internal/tools/skills/data/web-application-security/exploiting-template-injection-vulnerabilities/SKILL.md

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# Exploiting Template Injection Vulnerabilities

## When to Use

- During authorized penetration tests when user input is rendered through a server-side template engine
- When testing error pages, email templates, PDF generators, or report builders that include user-supplied data
- For assessing applications that allow users to customize templates or notification messages
- When identifying potential SSTI in parameters that reflect arithmetic results (e.g., `{{7*7}}` returns `49`)
- During security assessments of CMS platforms, marketing tools, or any application with templating functionality

### How to CONFIRM a Hit (avoid false negatives)
- The positive signal is **server-side evaluation of an expression**: an arithmetic probe is rendered as its result. Confirm `{{7*7}}` → `49`, `${7*7}` → `49`, `#{7*7}` → `49`, `<%= 7*7 %>` → `49`, `{7*7}` → `49`. The literal `7*7` staying in the response means no evaluation at that syntax (try the next).
- Distinguish SSTI from plain reflection/XSS: a reflected `7*7` is just echo; only a computed `49` (or a string-multiplication tell like `{{7*'7'}}` → `7777777`) proves template execution. Then fingerprint the engine BEFORE declaring impact.
- Fingerprint via the divergence test: `{{7*'7'}}` → `7777777` = Jinja2, `49` = Twig; `${7*7}` evaluating = Freemarker/Velocity/Spring EL; `#{7*7}` = Thymeleaf/Ruby. Engine-specific RCE only works after correct fingerprint.