jinja2-ssti-sanitizer 0.1.0

Detect and neutralize Jinja2 server-side template injection (SSTI) payloads

jinja2-ssti-sanitizer

Detect and neutralize Jinja2 server-side template injection (SSTI) payloads before they reach your templates.

Installation

pip install jinja2-ssti-sanitizer

For safe rendering helpers that use Jinja2's SandboxedEnvironment:

pip install jinja2-ssti-sanitizer[render]

Quick start

from jinja2_ssti_sanitizer import (
    is_jinja2_payload,
    sanitize_jinja2_input,
    render_safely,
)

# Detect SSTI attempts in user input
if is_jinja2_payload(user_input):
    raise ValueError("blocked")

# Escape delimiters and strip gadget fragments
result = sanitize_jinja2_input(user_input)
safe_text = result.sanitized

# Render a fixed template with a validated context
html = render_safely("Hello {{ name }}!", {"name": user_name})

API

Function	Description
detect_threats(value)	Returns threat level and matched rule names
is_jinja2_payload(value)	True when input matches SSTI patterns
sanitize_jinja2_input(value, mode="escape")	Neutralize input (escape, strip, or reject)
validate_template_variable(name, value)	Validate a single context value
validate_template_context(context)	Validate all string values in a render context
create_safe_environment()	SandboxedEnvironment with safe defaults
render_safely(template_source, context)	Render with validated context

Sanitization modes

• escape (default) — HTML-entity-encode {{, }}, {%, %}, {#, #} and strip gadget fragments
• strip — remove delimiter tokens and dangerous expressions
• reject — raise ValueError on HIGH or CRITICAL threats

Critical payloads (dunder chains, mro, subclasses, import/include tags, etc.) are always rejected when reject_critical=True (the default).

What it protects against

• Jinja2 variable, block, and comment delimiters
• Common gadget chains (__class__, mro, subclasses, config, request, attr filter, …)
• Unicode homoglyphs and zero-width bypass characters

Defense in depth

This library is a input-validation layer, not a substitute for secure design:

1. Never build template source from user-controlled input.
2. Use SandboxedEnvironment with autoescape enabled.
3. Sanitize or reject untrusted strings before they enter template context.

Development

git clone https://github.com/kjsxz/sanitizer-library.git
cd sanitizer-library
python -m venv .venv
source .venv/bin/activate
pip install -e ".[dev]"
pytest
python -m build

Publishing to PyPI

Releases are published automatically when a GitHub Release is created.

One-time setup

1. Create a PyPI project at pypi.org (or test.pypi.org first).
2. Configure trusted publishing on PyPI:
   • Publisher: GitHub Actions
   • Repository: kjsxz/sanitizer-library
   • Workflow: publish.yml
   • Environment: pypi
3. In GitHub repo settings, create an environment named pypi (optional approval gate).

Release flow

# Bump version in pyproject.toml and jinja2_ssti_sanitizer/__init__.py
git tag v0.1.0
git push origin v0.1.0

Then create a GitHub Release from the tag. The publish workflow uploads to PyPI.

Manual publish (maintainers):

pip install build twine
python -m build
twine upload dist/*

License

MIT — see LICENSE.