To fix a missing Access-Control-Allow-Origin header, add a narrowly scoped Apache Header rule in the .htaccess file that serves the API or assets, then verify the actual response—including any OPTIONS preflight. This works only when the host allows FileInfo overrides and Apache has mod_headers loaded. Use an exact frontend origin for private or credentialed requests; reserve * for public, anonymous access.
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The header is a browser permission, not an access-control system. WordPress authentication, authorization checks, nonces, and API permissions still have to protect the endpoint.
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What CORS changes in Apache
Cross-Origin Resource Sharing (CORS) is enforced by browsers. A page served from one origin—defined by scheme, host, and port—may request a resource from another origin, but the browser will expose the response to JavaScript only when the response contains an acceptable CORS policy.
Apache sends that policy as HTTP response headers. The most important one is Access-Control-Allow-Origin. A rule in .htaccess changes Apache’s response; it does not change the browser’s request policy and cannot grant a user permission they do not already have on the WordPress endpoint.
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For example, https://app.example.com, https://app.example.com:8443, and http://app.example.com are different origins. An allowed value must match the requesting origin exactly. Do not include a path such as /dashboard or append a trailing slash.
Check whether .htaccess can work on your server
Before editing anything, confirm the Apache prerequisites with your host or server administrator. A syntactically correct rule has no effect when the server ignores the file, and it can produce a 500 error when the directive is forbidden.
- Overrides must be enabled. Apache controls this with
AllowOverrideand, on newer configurations,AllowOverrideList. TheHeaderdirective belongs to theFileInfooverride class. mod_headersmust be loaded. Apache’sHeaderdirective is supplied by this module and is available in server, virtual-host, directory, and permitted.htaccesscontexts.- The file must be in the right directory. A
.htaccessfile applies to its directory and descendants when overrides are enabled. A rule in a WordPress document-root file will not automatically govern a separate virtual host or a directory served by another application. - A proxy or CDN may be the final response layer. Even if Apache adds a header, a cache or reverse proxy can replace, remove, or duplicate it.
If you cannot verify these settings, ask the host to confirm that FileInfo directives are allowed and that mod_headers is active. When the host sets AllowOverride None, move the rule to the virtual-host/server configuration through the administrator rather than trying to force it into WordPress.
Back up and scope the change
- Download or copy the current
.htaccessfile before making edits. Keep a dated, known-good version so a syntax error can be reverted immediately. - Identify the URL path that needs cross-origin access: for example, a REST endpoint, a GraphQL route, JavaScript files, fonts, or images. Put the rule in the document-root file only when the whole site needs the policy; otherwise use the narrower directory that serves those resources.
- Inspect the current response first. WordPress core, a plugin, application code, a CDN, or another Apache context may already add CORS headers. Adding a second policy can create duplicate
Access-Control-Allow-Originvalues that browsers reject.
Keep the smallest possible origin, method, header, and resource scope. MDN’s CORS guidance recommends allowing the minimum number of origins and resources required for the site to function.
Allow a public, non-credentialed resource
For a genuinely public asset or API that does not use cookies, HTTP authentication, or other credentials, a wildcard is the simplest policy:
<IfModule mod_headers.c>
Header always set Access-Control-Allow-Origin "*"
</IfModule>Header always set is useful when you want the header on error responses as well as successful responses. The <IfModule> wrapper prevents an unknown-module error, but it also means the rule silently does nothing when mod_headers is absent; confirm the module rather than treating a missing header as proof that the browser is at fault.
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Do not apply this rule indiscriminately to every WordPress response. A site-wide wildcard can expose responses that were intended for same-origin pages, and it does not make a private endpoint safe. Limit it to the API or asset directory whenever possible.
Allow one private frontend origin
For a known application frontend, return its exact origin:
<IfModule mod_headers.c>
Header always set Access-Control-Allow-Origin "https://app.example.com"
Header always set Vary "Origin"
</IfModule>Replace the example with the real scheme, hostname, and port. Do not write https://app.example.com/, add a URL path, or list several origins separated by commas; the response header accepts one origin value or the wildcard.
Vary: Origin tells shared caches that the representation can differ according to the request’s Origin header. It is required whenever the server selects an explicit origin dynamically and is a prudent cache signal for policies that may vary by origin.
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Support several origins safely
Apache cannot safely authorize several private origins by blindly reflecting whatever value the browser sends. If production, staging, and a partner application are all legitimate clients, compare the incoming Origin against a fixed allowlist and emit a single matching value.
The comparison can be implemented in Apache server configuration, WordPress code, or the application that owns the endpoint. The important properties are:
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- The allowlist is fixed and reviewed; arbitrary input is never copied into
Access-Control-Allow-Origin. - Only one approved origin is emitted for each response.
Vary: Originis sent because the response changes according to the request origin.- An unapproved origin receives no allow-origin header (or an intentional denial), rather than being reflected.
When the host does not permit the needed conditional directives in .htaccess, put this logic in the virtual-host configuration or WordPress endpoint code. A static rule is preferable to a complex workaround that is difficult to audit.
Handle preflight OPTIONS requests
Browsers send a preflight OPTIONS request before many cross-origin requests, especially when the method is not a simple method or the request includes headers such as Authorization. The preflight asks whether the actual method and request headers are allowed.
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Add only the values the application really uses:
<IfModule mod_headers.c>
Header always set Access-Control-Allow-Methods "GET, POST, OPTIONS"
Header always set Access-Control-Allow-Headers "Content-Type, Authorization"
</IfModule>The example permits GET, POST, and OPTIONS, and allows the two named request headers. Do not copy this list unchanged if the endpoint accepts fewer methods or does not send an authorization header. Match the browser’s requested method and header names; otherwise the preflight can fail even though the main response looks correct.
These headers do not replace Access-Control-Allow-Origin. The preflight response needs an origin that matches the frontend’s origin, along with any required method and header permissions. Ensure that the server returns a usable status for OPTIONS instead of redirecting it to a login page or a trailing-slash URL.
Configure credentialed requests correctly
Cookies, HTTP authentication, and explicitly credentialed fetch requests require a specific origin. They cannot be used with Access-Control-Allow-Origin: *. Browsers reject a wildcard when credentials are included.
Use an exact origin and explicitly authorize credentials:
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<IfModule mod_headers.c>
Header always set Access-Control-Allow-Origin "https://app.example.com"
Header always set Access-Control-Allow-Credentials "true"
Header always set Vary "Origin"
</IfModule>The frontend must also opt in to credentials (for example, a Fetch request with credentials: "include"), and the server must set cookie attributes appropriate for the deployment. CORS does not bypass WordPress login checks, nonce validation, capability checks, or API authentication. A permissive CORS rule only determines whether browser JavaScript can read a response after the server has processed the request.
Do not use Access-Control-Allow-Origin: null as a workaround. A hostile document can obtain a null origin, so treating it as trusted weakens the boundary.
Understand WordPress’s own CORS behavior
WordPress includes send_origin_headers(), which handles OPTIONS requests and can send access-control headers for an allowed origin or return a 403 response when the origin is not allowed. A plugin, theme, or custom REST endpoint may also add its own headers.
Inspect the final response before adding Apache directives. If WordPress already emits the correct policy, changing .htaccess may create duplicate values. If the WordPress layer intentionally denies an origin, an Apache rule that adds a broad header can produce a misleading response and expose an endpoint that the application meant to restrict.
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1Fix the driver behind crashes, sound loss and screen glitches2Repair Windows errors before they cause bigger problems3Scan for outdated or missing drivers - takes under a minuteChoose one authoritative layer for the policy whenever possible. Apache is useful for static assets or a host-wide baseline; endpoint code is usually better when authorization depends on the current user, route, or tenant.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Test the response, not just the configuration file
Use browser developer tools or an HTTP client against the real public URL. Test both the preflight and the actual request, and follow redirects because a redirect response can lack the required headers.
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- Open the browser’s Network panel and reproduce the failing request. Select the
OPTIONSentry, if present, and record its status and response headers. - Confirm that
Access-Control-Allow-Origincontains exactly the requesting origin—or*for a non-credentialed public request—and appears only once. - For preflighted calls, verify
Access-Control-Allow-Methodscontains the requested method andAccess-Control-Allow-Headerscontains every requested non-simple header. - Inspect the actual
GET,POST, or other request. The final response also needs the allow-origin header; a successful preflight alone is not enough. - When the response varies by origin, verify
Vary: Origin. Check whether a CDN or proxy cached a response generated for a different origin. - Compare responses from an allowed origin, an unapproved origin, and a same-origin request. This reveals accidental reflection and confirms that the rule is scoped as intended.
An HTTP client can send an origin explicitly. For example:
curl -i -H "Origin: https://app.example.com" https://www.example.com/api/endpoint
curl -i -X OPTIONS
-H "Origin: https://app.example.com"
-H "Access-Control-Request-Method: POST"
-H "Access-Control-Request-Headers: Content-Type, Authorization"
https://www.example.com/api/endpointReplace the URL and requested method or headers with those used by your application. The command shows headers returned by the server; it does not emulate every browser credential rule.
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500 Internal Server Error
A 500 immediately after editing usually means Apache rejected a directive. The host may disallow the FileInfo override class, the directive may be unavailable because mod_headers is not loaded, or the file may contain a syntax error. Restore the backup, then ask the administrator to enable the directive or place the rule in server configuration.
The rule has no effect
The file may be ignored because AllowOverride None is active, may be in a directory that does not serve the requested resource, or may be overridden by a proxy/CDN. Confirm which server generated the final response and test the exact endpoint rather than a different WordPress page.
Duplicate or conflicting allow-origin headers
Search the response chain for headers added by WordPress, a security or cache plugin, application code, another Apache context, and the CDN. Remove all but the intended policy. Browsers need one coherent allow-origin value; two different values are not merged into a valid permission.
Preflight still fails
Read the OPTIONS response. Check its status, redirects, allow-origin value, allowed method, and allowed request headers. Add only the missing method or header and ensure the spelling matches the browser’s Access-Control-Request-Headers value. A login redirect, firewall challenge, or 403 on OPTIONS must be fixed at that layer.
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Replace * with the exact frontend origin, send Access-Control-Allow-Credentials: true, and make the browser request credentialed. Verify that the endpoint’s authentication and cookie settings permit the cross-origin deployment.
A cache returns the wrong origin
If different callers receive different allow-origin values, send Vary: Origin and configure the cache to respect it. Purge an already-cached response after changing the policy.
The API is on another server
A local WordPress .htaccess file cannot add headers to a remote API response. The server that owns that API must configure CORS, or your architecture must route requests through a server you control. A browser extension or local development proxy may hide the issue during testing but does not fix production behavior.
Quick Recap
Choose the right configuration layer
| Layer | Best use | Key limitation |
|---|---|---|
Apache .htaccess |
Simple, directory-scoped policies for assets or an endpoint when the host permits FileInfo. |
Unavailable or restricted on some hosts; can conflict with application and cache headers. |
| Apache virtual-host/server configuration | Central policies, conditional origin selection, and environments where overrides are disabled. | Requires administrator access and careful configuration reloads. |
| WordPress/plugin or endpoint code | Policies that depend on route, user, tenant, or application allowlists. | Must handle every response path, including errors and OPTIONS. |
| CDN or reverse proxy | Policies applied at the edge, with cache behavior controlled alongside headers. | Can mask origin-server changes and introduce duplicate or stale headers. |
Security rules to keep in place
- Allow the minimum origins and resources necessary for the feature.
- Use
*only for public, non-credentialed responses. - Use an exact origin plus
Access-Control-Allow-Credentials: truefor cookie- or authentication-based browser requests. - Never reflect an arbitrary
Originheader and never trustnullas a shortcut. - Keep WordPress permissions, nonces, authentication, rate limits, and authorization checks independent of CORS.
- Review preflight methods and headers whenever the frontend changes; a broad permanent list makes future mistakes harder to detect.
A practical deployment sequence
- Record the failing URL, requesting origin, method, credentials mode, and browser error.
- Inspect the existing
OPTIONSand actual responses for current CORS headers and duplicates. - Confirm
AllowOverride/AllowOverrideListandmod_headerswith the administrator. - Back up
.htaccessand add the narrowest rule in the directory serving the resource. - Choose a wildcard only for public anonymous access; otherwise use an exact origin and add credential or preflight headers only when required.
- Test allowed, denied, preflight, redirect, error, and cached responses.
- Remove conflicting headers at WordPress, plugin, CDN, or Apache layers and document the final owner of the policy.
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