generic.nginx.security.header-redefinition.header-redefinition

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The 'add_header' directive is called in a 'location' block after headers have been set at the server block. Calling 'add_header' in the location block will actually overwrite the headers defined in the server block, no matter which headers are set. To fix this, explicitly set all headers or set all headers in the server block.

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Defintion

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rules:
  - id: header-redefinition
    patterns:
      - pattern-inside: |
          server {
            ...
            add_header ...;
            ...
            ...
          }
      - pattern-inside: |
          location ... {
            ...
            ...
          }
      - pattern: add_header ...;
    paths:
      include:
        - "*.conf"
        - "*.vhost"
        - sites-available/*
        - sites-enabled/*
    languages:
      - generic
    severity: WARNING
    message: The 'add_header' directive is called in a 'location' block after
      headers have been set at the server block. Calling 'add_header' in the
      location block will actually overwrite the headers defined in the server
      block, no matter which headers are set. To fix this, explicitly set all
      headers or set all headers in the server block.
    metadata:
      cwe:
        - "CWE-16: CWE CATEGORY: Configuration"
      references:
        - https://github.com/yandex/gixy/blob/master/docs/en/plugins/addheaderredefinition.md
      category: security
      technology:
        - nginx
      confidence: LOW
      owasp:
        - A06:2017 - Security Misconfiguration
        - A05:2021 - Security Misconfiguration
      subcategory:
        - audit
      likelihood: LOW
      impact: LOW
      license: Commons Clause License Condition v1.0[LGPL-2.1-only]

Examples

header-redefinition.conf

server {
  listen 80;
  # ok: header-redefinition
  add_header X-Frame-Options "DENY" always;
  location / {
      return 200 "index";
  }

  location /new-headers {
    # Add special cache control
    # ruleid: header-redefinition
    add_header Cache-Control "no-cache, no-store, max-age=0, must-revalidate" always;
    # ruleid: header-redefinition
    add_header Pragma "no-cache" always;

    return 200 "new-headers";
  }
}