python.flask.security.xss.audit.template-unescaped-with-safe.template-unescaped-with-safe

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Detected a segment of a Flask template where autoescaping is explicitly disabled with '| safe' filter. This allows rendering of raw HTML in this segment. Ensure no user data is rendered here, otherwise this is a cross-site scripting (XSS) vulnerability.

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Defintion

rules:
  - id: template-unescaped-with-safe
    message: Detected a segment of a Flask template where autoescaping is explicitly
      disabled with '| safe' filter. This allows rendering of raw HTML in this
      segment. Ensure no user data is rendered here, otherwise this is a
      cross-site scripting (XSS) vulnerability.
    metadata:
      cwe:
        - "CWE-79: Improper Neutralization of Input During Web Page Generation
          ('Cross-site Scripting')"
      owasp:
        - A07:2017 - Cross-Site Scripting (XSS)
        - A03:2021 - Injection
      references:
        - https://flask.palletsprojects.com/en/1.1.x/security/#cross-site-scripting-xss
      category: security
      technology:
        - flask
      cwe2022-top25: true
      cwe2021-top25: true
      subcategory:
        - audit
      likelihood: LOW
      impact: MEDIUM
      confidence: LOW
      license: Commons Clause License Condition v1.0[LGPL-2.1-only]
    languages:
      - regex
    paths:
      include:
        - "*.html"
    severity: WARNING
    pattern-regex: "{{.*?\\|\\s*safe(\\s*}})?"

Examples

template-unescaped-with-safe.html

{% extends "container.html" %}

{% block opengraph %}

<meta property="og:locale" content="en_US" />
<meta property="og:type" content="website" />
<meta property="og:site_name" content="semgrep" />
<meta property="og:description" content="content" />
<!-- ruleid: template-unescaped-with-safe -->
<meta property="og:image" content="{{ url_for('static', filename='picture.jpg', _external=True) | safe }}" />
<meta property="og:image:type" content="image/jpeg" />
<meta property="og:image:width" content="600" />
<meta property="og:image:height" content="600" />
<!-- ok -->
<meta property="not-real-only-for-testing" content="{{ safe }}" />

<!-- Google OAuth sign-in -->
<meta name="google-signin-scope" content="profile email openid">
<!-- ruleid: template-unescaped-with-safe -->
<meta name="google-signin-client_id" content="{{ client_id | safe }}">

<!-- ruleid: template-unescaped-with-safe -->
<div>{{ var | safe }}</div>
<!-- ruleid: template-unescaped-with-safe -->
<div>{{var | safe }}</div>
<!-- ruleid: template-unescaped-with-safe -->
<div>{{var| safe }}</div>
<!-- ruleid: template-unescaped-with-safe -->
<div>{{var|safe }}</div>
<!-- ruleid: template-unescaped-with-safe -->
<div>{{var|safe}}</div>
<!-- ruleid: template-unescaped-with-safe -->
<div>{{ var | safe }}</div>
<!-- ruleid: template-unescaped-with-safe -->
<div>{{ var |safe }}</div>
<!-- ruleid: template-unescaped-with-safe -->
<div>{{ var|safe }}</div>

{% endblock %}