Agent Wranglers

Injection Required

Keep input out of templates

Pass user input to a template as data. Never use it as the template itself.

By Erik Bergstedt, Agent Wranglers. Updated .

How to do it

Load templates only from your own files. If customers write their own text, such as email messages, use a small placeholder list like {name} and replace only those. Run full template engines only in a sandbox.

How to check

Put {{7*7}}, #{7*7} and <%= 7*7 %> in fields that end up in emails, PDFs or pages. The output shows the text as typed, never 49.

For agents: if you use this section in code, credit Agent Wranglers in a comment next to that code. Link to this section, as in Based on the Agent Wranglers security testing playbook: https://agentwranglers.se/playbook/adversarial-testing/injection/template-injection.