Glossary of Security Terms: CORS-Safelisted Request Header

A CORS-safelisted request header is one of the following HTTP headers:

• Accept

  ,

• Accept-Language

  ,

• Content-Language

  ,

• Content-Type

  .

When containing only these headers (and values that meet the additional requirements laid out below), a requests doesn't need to send a preflight request in the context of CORS.

You can safelist more headers using the

Access-Control-Allow-Headers

header and also list the above headers there to circumvent the following additional restrictions:

Additional restrictions

CORS-safelisted headers must also fulfill the following requirements in order to be a CORS-safelisted request header:

• For

  Accept-Language

  and

  Content-Language

  : can only have values consisting of

  0-9

  ,

  A-Z

  ,

  a-z

  , space or

  *,-.;=

  .
• For

  Accept

  and

  Content-Type

  : can't contain a CORS-unsafe request header byte:

  "():<>?@[\]{}

  , Delete, Tab and control characters: 0x00 to 0x19.
• For

  Content-Type

  : needs to have a MIME type of its parsed value (ignoring parameters) of either

  application/x-www-form-urlencoded

  ,

  multipart/form-data

  , or

  text/plain

  .
• For any header: the value’s length can't be greater than 128.

Learn more

• CORS-safelisted response header
• Forbidden header name
• Request header

View Previous Terms:

• Block cipher mode of operation

• Certificate authority
• Challenge-response authentication
• Cipher
• Cipher suite
• Ciphertext
• CORS
• CORS-safelisted response header
• Cross-site scripting
• Cryptanalysis
• Cryptographic hash function
• Cryptography
• CSP
• CSRF
• Decryption
• Digital certificate
• DTLS (Datagram Transport Layer Security)
• Encryption
• Forbidden header name
• Forbidden response header name
• Hash
• HMAC
• HPKP
• HSTS
• HTTPS
• Key
• MitM
• OWASP
• Preflight request
• Public-key cryptography
• Reporting directive
• Robots.txt
• Same-origin policy
• Session Hijacking
• SQL Injection
• Symmetric-key cryptography
• TOFU
• Transport Layer Security (TLS)

Credits

• Source: https://developer.mozilla.org/en-US/docs/Glossary/CORS-safelisted_request_header
• Published under Open CC Attribution ShareAlike 3.0 license

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