Description
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.
Potential Impact
Integrity
Execute Unauthorized Code or Commands
Mitigations & Prevention
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.
Use the template engine's sandbox or restricted mode, if available.
Detection Methods
- Automated Static Analysis High — Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then sea
Real-World CVE Examples
| CVE ID | Description |
|---|---|
| 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 |
| 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
Frequently Asked Questions
What is CWE-1336?
CWE-1336 (Improper Neutralization of Special Elements Used in a Template Engine) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Base-level weakness. 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 templat...
How can CWE-1336 be exploited?
Attackers can exploit CWE-1336 (Improper Neutralization of Special Elements Used in a Template Engine) to execute unauthorized code or commands. This weakness is typically introduced during the Architecture and Design, Implementation phase of software development.
How do I prevent CWE-1336?
Key mitigations include: 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.
What is the severity of CWE-1336?
CWE-1336 is classified as a Base-level weakness (Medium abstraction). It has been observed in 10 real-world CVEs.