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Threat Model Analysis for pallets/jinja

Threat: Server-Side Template Injection (SSTI) - Code Execution

  • Description: An attacker crafts malicious input that, when incorporated into a Jinja template, is interpreted as Jinja syntax rather than plain text. The attacker uses Jinja delimiters (e.g., {{ ... }}, {% ... %}) to inject Python code, which is then executed on the server during template rendering. The attacker aims to execute system commands, read files, or otherwise compromise the server.

  • Impact: Complete server compromise (Remote Code Execution - RCE), data exfiltration, denial of service, information disclosure.

  • Jinja Component Affected:

    • Environment.from_string(): If user input is passed directly.
    • Template.render(): When rendering a template with unsanitized user input.
    • render_template_string() (Flask-specific, uses Jinja): Highly dangerous with user-provided strings.
    • Any function loading/rendering templates if content/variables are user-influenced.

  • Risk Severity: Critical

  • Mitigation Strategies:

    • Strict Input Validation: Validate and sanitize all user input before template use. Whitelist (allow only known-good) instead of blacklist.
    • Context-Aware Auto-Escaping: Enable and correctly configure Jinja's auto-escaping. Understand its limitations; manually escape where needed.
    • Avoid render_template_string with User Input: Prefer file-based templates. If unavoidable, treat input as highly untrusted.
    • Sandboxing (Limited): Use SandboxedEnvironment, but do not rely on it solely. Bypasses are possible.
    • Least Privilege: Run the application with minimal necessary privileges.
    • Regular Updates: Keep Jinja and dependencies updated.

Threat: Server-Side Template Injection (SSTI) - Data Leakage

  • Description: The attacker uses Jinja syntax to access and exfiltrate sensitive data available within the template's context (e.g., {{ config.SECRET_KEY }}). This is a variation of SSTI, focusing on data exposure rather than code execution.

  • Impact: Exposure of sensitive data (API keys, database credentials, internal data), leading to further attacks.

  • Jinja Component Affected: Same as SSTI - Code Execution. The vulnerability is in how user input is handled within any template rendering function.

  • Risk Severity: High

  • Mitigation Strategies: Same as SSTI - Code Execution. Preventing any template injection prevents both.

Threat: Using Untrusted Template Sources

  • Description: The application loads Jinja templates from an untrusted source (user-uploaded files, attacker-controlled database fields, external URLs). The attacker provides a malicious template with arbitrary Jinja code.

  • Impact: Identical to successful SSTI (code execution, data leakage).

  • Jinja Component Affected:

    • FileSystemLoader: If configured to load from an untrusted directory.
    • PackageLoader: If the package/module path is user-influenced.
    • DictLoader: If the template dictionary is from untrusted data.
    • FunctionLoader: If the function returns untrusted content.
    • ChoiceLoader or PrefixLoader: If underlying loaders use untrusted sources.
    • Environment.from_string(): If the template string is from an untrusted source.

  • Risk Severity: Critical

  • Mitigation Strategies:

    • Load Templates from Trusted Locations Only: Use the application's filesystem, a controlled, secure directory.
    • Never Load Templates from User Input: Do not allow uploads or path specifications.
    • Avoid Dynamic Template Loading: Avoid loading based on user input or external data.
    • Template Content Validation (Extremely Difficult): If absolutely necessary, implement extremely rigorous validation before rendering. Avoid if possible.