Improper Neutralization of Special Elements Used in a Template Engine

Opis

The product uses a template engine to insert or process externally-influenced input, but it does not neutralize or incorrectly neutralizes special elements or syntax that can be interpreted as template expressions or other code directives when processed by the engine.

Many web applications use template engines that allow developers to insert externally-influenced values into free text or messages in order to generate a full web page, document, message, etc. Such engines include Twig, Jinja2, Pug, Java Server Pages, FreeMarker, Velocity, ColdFusion, Smarty, and many others - including PHP itself. Some CMS (Content Management Systems) also use templates.

Template engines often have their own custom command or expression language. If an attacker can influence input into a template before it is processed, then the attacker can invoke arbitrary expressions, i.e. perform injection attacks. For example, in some template languages, an attacker could inject the expression "{{7*7}}" and determine if the output returns "49" instead. The syntax varies depending on the language.

In some cases, XSS-style attacks can work, which can obscure the root cause if the developer does not closely investigate the root cause of the error.

Template engines can be used on the server or client, so both "sides" could be affected by injection. The mechanisms of attack or the affected technologies might be different, but the mistake is fundamentally the same.

Inne nazwy

Server-Side Template Injection / SSTI

This term is used for injection into template engines being used by a server.

Client-Side Template Injection / CSTI

This term is used for injection into template engines being used by a client.

Skutki

• Integrity

  Execute Unauthorized Code or Commands

Zapobieganie

• Architecture and Design

  Choose a template engine that offers a sandbox or restricted mode, or at least limits the power of any available expressions, function calls, or commands.

• Implementation

  Use the template engine's sandbox or restricted mode, if available.

Przykłady podatności

• CVE-2024-34359 Chain: Python bindings for LLM library do not use a sandboxed environment when parsing a template and constructing a prompt, allowing jinja2 Server Side Template Injection and code execution - one variant of a "prompt injection" attack.
• CVE-2017-16783 server-side template injection in content management server
• CVE-2020-9437 authentication / identity management product has client-side template injection
• CVE-2020-12790 Server-Side Template Injection using a Twig template
• CVE-2021-21244 devops platform allows SSTI
• CVE-2020-4027 bypass of Server-Side Template Injection protection mechanism with macros in Velocity templates
• CVE-2020-26282 web browser proxy server allows Java EL expressions from Server-Side Template Injection
• CVE-2020-1961 SSTI involving mail templates and JEXL expressions
• CVE-2019-19999 product does not use a "safe" setting for a FreeMarker configuration, allowing SSTI
• CVE-2018-20465 product allows read of sensitive database username/password variables using server-side template injection

Słabość nadrzędna

• CWE-94 Improper Control of Generation of Code ('Code Injection')

Kiedy powstaje

• Architecture and Design — The developer might choose a template engine that makes it easier for programmers to write vulnerable code.
• Implementation — The programmer might not use engine's built-in sandboxes or other capabilities to escape or otherwise prevent template injection from untrusted input.

Dotyczy

Java, PHP, Python, JavaScript, Interpreted, Not OS-Specific, Not Technology-Specific, AI/ML, Client Server

Uwagi

Since expression languages are often used in templating languages, there may be some overlap with CWE-917 (Expression Language Injection). XSS (CWE-79) is also co-located with template injection.

The interrelationships and differences between CWE-917 and CWE-1336 need to be further clarified.

Źródła

1. Server-Side Template Injection — James Kettle, 2015
2. Server-Side Template Injection: RCE For The Modern Web App — James Kettle, 2015