mcp-server-semgrep/semgrep-rules/python/flask/security/dangerous-template-string.yaml

MCP Server for Semgrep Integration - static code analysis with AI

rules:
- id: dangerous-template-string
  message: >-
    Found a template created with string formatting.
    This is susceptible to server-side template injection
    and cross-site scripting attacks.
  metadata:
    cwe:
    - "CWE-96: Improper Neutralization of Directives in Statically Saved Code ('Static Code Injection')"
    owasp:
    - A03:2021 - Injection
    references:
    - https://nvisium.com/blog/2016/03/09/exploring-ssti-in-flask-jinja2.html
    - https://pequalsnp-team.github.io/cheatsheet/flask-jinja2-ssti
    category: security
    technology:
    - flask
    subcategory:
    - audit
    likelihood: LOW
    impact: MEDIUM
    confidence: LOW
  languages: [python]
  severity: ERROR
  pattern-either:
  - pattern: |
      $V = "...".format(...)
      ...
      flask.render_template_string($V, ...)
  - pattern: |
      $V = "...".format(...)
      ...
      return flask.render_template_string($V, ...), $MORE
  - pattern: |
      $V = "..." % $S
      ...
      flask.render_template_string($V, ...)
  - pattern: |
      $V = "..." % $S
      ...
      return flask.render_template_string($V, ...), $MORE
  - pattern: |
      $V = "..."
      ...
      $V += $O
      ...
      flask.render_template_string($V, ...)
  - pattern: |
      $V = "..."
      ...
      $V += $O
      ...
      return flask.render_template_string($V, ...), $MORE
  - pattern: |
      $V = f"...{$X}..."
      ...
      flask.render_template_string($V, ...)
  - pattern: |
      $V = f"...{$X}..."
      ...
      return flask.render_template_string($V, ...), $CODE