Compliance-trestle (Trestle) is a Python SDK and command-line tool for managing OSCAL compliance documents. In versions prior to 3.12.4 and 4.0.0 through 4.0.3, the custom Jinja2 include tags mdsection_include and md_clean_include re-parse the content of an included Markdown file as Jinja2 template code in a non-sandboxed environment, allowing server-side template injection that can lead to arbitrary code execution. The MDSectionInclude and MDCleanInclude tags in Trestle/core/jinja/tags.py pass included file content to Parser(self.environment, ...).parse(), splicing it into the host template's compilation, and the environment is a plain jinja2.Environment rather than a SandboxedEnvironment, so any expressions in the file are evaluated with full access to the usual SSTI gadget chain. Because Trestle's Markdown writers emit OSCAL prose and component-description fields verbatim, applying delimiter neutralization only to parameter tables, attacker-controlled OSCAL data such as a control statement, part prose, or component description containing Jinja2 syntax flows into an included Markdown file and is executed when the include tag re-parses it. This issue is fixed in version 4.1.0.