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sast-ssti

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Detect Server-Side Template Injection (SSTI) vulnerabilities in a codebase using a three-phase approach: recon (find template rendering sites that use dynamic strings), batched verify (trace user input to those sites in parallel subagents, 3 candidates each), and merge (consolidate batch results). Requires sast/architecture.md (run sast-analysis first). Outputs findings to sast/ssti-results.md. Use when asked to find SSTI or template injection bugs.

sast-files/.agents/skills/sast-ssti/SKILL.md

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Last checked
Nov 9, 2026

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Oct 23, 2026
License
MIT

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# 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 three-phase approach with subagents: **recon** (find candidate rendering sites where the template string is dynamic), **batched verify** (trace whether user input reaches each site's template argument, in parallel batches of 3), and **merge** (consolidate batch results into the final report).

**Prerequisites**: `sast/architecture.md` must exist. Run the analysis skill first if it doesn't.

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## 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.*
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