fix(security): enable Jinja2 autoescape to prevent XSS in gepa sample

[k4w-wak]

Security Fix: XSS via Jinja2 Template Injection (CWE-79)

Vulnerability

contributing/samples/gepa/rater_lib.py instantiates jinja2.Environment() without autoescape=True. The companion template rubric_validation_template.txt renders {{user_input}} and {{model_response}} without escaping.

Impact

Since ADK is Google's official framework for building AI agents, developers copy/adapt this sample code into production web applications. Unescaped user-controlled input in Jinja2 templates enables:

• Cross-Site Scripting (XSS) — Arbitrary JavaScript execution in browsers
• Session Hijacking — Steal cookies/tokens if rendered in web context
• Phishing — Inject fake login forms

Proof of Concept

# user_input: <script>alert("XSS")</script>
# Renders as: <main_prompt><script>alert("XSS")</script></main_prompt>

# model_response: <img src=x onerror=alert("XSS from model")>
# Renders as: <responses><img src=x onerror=alert("XSS from model")></responses>

Changes

1. rater_lib.py:170 — jinja2.Environment() → jinja2.Environment(autoescape=True)
2. rubric_validation_template.txt:158 — {{user_input}} → {{user_input|e}}
3. rubric_validation_template.txt:163 — {{model_response}} → {{model_response|e}}

Defense in depth: autoescape=True provides baseline protection, explicit |e filters ensure escaping even if autoescape is later disabled.

References

• CWE-79: Cross-site Scripting (XSS)
• OWASP A7:2017 — Cross-site Scripting
• Jinja2 docs: https://jinja.palletsprojects.com/en/3.1.x/api/#autoescaping

[google-cla]

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[k4w-wak]

I have signed the Google CLA. Please re-check.

[rohityan]

Hi @k4w1992-lgtm , Thank you for your contribution! We appreciate you taking the time to submit this pull request. Your PR has been received by the team and is currently under review. We will provide feedback as soon as we have an update to share.

[rohityan]

Hi @Jacksunwei , can you please review this.

[adk-bot]

Thank you @k4w-wak for your contribution! 🎉

Your changes have been successfully imported and merged via Copybara in commit a721c1e.

Closing this PR as the changes are now in the main branch.