CWE WEAKNESSES  /  CWE-1336

CWE-1336

Improper Neutralization of Special Elements Used in a Template Engine

What it is

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

Impact

Mitigations

• [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.

Real-world CVE examples

• 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 Templat
• 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

Related weaknesses

Source: MITRE CWE. View on cwe.mitre.org →