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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Require preflight for non-standard CORS-safelisted request headers Accept, Accept-Language, and Content-Language"
href="https://bugs.webkit.org/show_bug.cgi?id=165178">165178</a>
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<th>Summary</th>
<td>Require preflight for non-standard CORS-safelisted request headers Accept, Accept-Language, and Content-Language
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<th>Classification</th>
<td>Unclassified
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<th>Product</th>
<td>WebKit
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<th>Version</th>
<td>WebKit Nightly Build
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<th>Hardware</th>
<td>Unspecified
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<th>OS</th>
<td>Unspecified
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>Normal
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<th>Priority</th>
<td>P2
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<th>Component</th>
<td>WebCore Misc.
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<th>Assignee</th>
<td>webkit-unassigned@lists.webkit.org
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<th>Reporter</th>
<td>wilander@apple.com
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<p>
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<pre>Fetch currently only restricts the header Content-Type for simple requests: <a href="https://fetch.spec.whatwg.org/#cors-safelisted-request-header">https://fetch.spec.whatwg.org/#cors-safelisted-request-header</a>
This means simple CORS requests can send unexpected characters in Accept, Accept-Language, and Content-Language header values.
RFC 7231 implies restrictions on these header values:
Accept <a href="https://tools.ietf.org/html/rfc7231#section-5.3.2">https://tools.ietf.org/html/rfc7231#section-5.3.2</a>
Accept-Language <a href="https://tools.ietf.org/html/rfc7231#section-5.3.5">https://tools.ietf.org/html/rfc7231#section-5.3.5</a>
Content-Language <a href="https://tools.ietf.org/html/rfc7231#section-3.1.3.2">https://tools.ietf.org/html/rfc7231#section-3.1.3.2</a>
As per discussions in the W3C WebAppSec group we should try to restrict these header values to help protect servers that do not expect simple CORS requests.
Non-standard header values should trigger a preflight and require the headers to be whitelisted in the response's Access-Control-Allow-Headers.</pre>
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