Server-Side Template Injection (SSTI) Pattern Regex for JavaScript

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching server-side template injection (ssti) pattern, ported and verified for JavaScript. In security-sensitive code, using an unverified regex can open the door to both false positives and denial-of-service attacks. The snippet below is ready to drop into your JavaScript project — whether you're validating in an Express middleware, a Next.js API route, or a client-side form.

Javascript Implementation

// Server-Side Template Injection (SSTI) Pattern
// ReDoS-safe | RegexVault — Security > Injection Patterns

const serversideTemplateInjectionSstiPatternRegex = /(?:\{\{[^}]*\}\}|\{%[^%]*%\}|\$\{[^}]*\}|#\{[^}]*\}|<#[^>]*>|@\{[^}]*\}|\[\[.*?\]\]|\{#[^}]*#\}|\{\{7\*7\}\}|\{\{config\}\}|\{\{self\}\}|__class__|__mro__|__import__)/i;

function validateServersideTemplateInjectionSstiPattern(input: string): boolean {
  return serversideTemplateInjectionSstiPatternRegex.test(input);
}

// Example
console.log(validateServersideTemplateInjectionSstiPattern("{{7*7}}")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Security > Injection Patterns category and carries a ReDoS-safe certification. That matters for JavaScript developers because especially critical in long-running Node.js event loops where a ReDoS vulnerability can block the entire process. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

Template engines: Jinja2/Twig/Nunjucks use {{ }}, {% %}, Freemarker uses ${}, Ruby ERB uses <%=%>. The probe {{7*7}} (expected result 49) is the canonical SSTI detection test. __class__ and __mro__ are Python object introspection used in Jinja2 sandbox escapes.