fix: prevent SSTI by switching to SandboxedEnvironment#74
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Templates are rendered in an unsandboxed Jinja2 environment, so passing untrusted user input as template text allows arbitrary code execution. Document the safe pattern (variables) vs the unsafe one (raw user strings). Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Switch from jinja2.Environment to jinja2.sandbox.SandboxedEnvironment. This blocks access to dunder attributes in templates, preventing SSTI payloads from reaching __builtins__ and executing arbitrary code. All existing tests pass unchanged. Add a regression test that verifies the canonical SSTI payload raises an exception. Also document that templates are trusted code and that user-supplied strings must never be passed as template text. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Pull request overview
This PR aims to mitigate Server-Side Template Injection (SSTI) risks in Banks prompt rendering by moving the global Jinja2 environment to Jinja2’s sandbox, adding a regression test for a canonical SSTI payload, and documenting safe/unsafe template usage patterns.
Changes:
- Switch global Jinja environment from
jinja2.Environmenttojinja2.sandbox.SandboxedEnvironment. - Add a regression test intended to ensure a known SSTI/RCE-style payload is blocked.
- Add/extend documentation warning against rendering user-supplied template text.
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.
| File | Description |
|---|---|
src/banks/env.py |
Uses SandboxedEnvironment for the global Jinja environment to reduce SSTI risk. |
tests/test_prompt.py |
Adds a regression test for an SSTI payload being blocked at render time. |
docs/prompt.md |
Adds a warning about treating templates as trusted code, but currently describes the environment incorrectly. |
docs/index.md |
Adds a “Security” section explaining safe vs unsafe patterns, but wording should reflect sandboxing. |
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Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
…lect SandboxedEnvironment Agent-Logs-Url: https://github.com/masci/banks/sessions/de6273d5-80bf-468c-8853-feeb273a7294 Co-authored-by: masci <7241+masci@users.noreply.github.com>
e2e tests require an OpenAI API key that is no longer valid. Python 3.9 is EOL (Oct 2025) and newer virtualenv drops support for it. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Coverage is 94.769% — docs/template-security-warning into main. No base build found for |
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Summary
jinja2.Environmenttojinja2.sandbox.SandboxedEnvironmentinsrc/banks/env.py— blocks dunder attribute traversal in templates, preventing SSTI/RCE payloads from reaching__builtins__Test plan
SandboxedEnvironmenttest_ssti_blockedconfirms the exploit payload raisesSecurityErrorhatch run docs build)🤖 Generated with Claude Code