The http.cors.expose-headers setting in Elasticsearch controls which HTTP headers are exposed to the browser when making Cross-Origin Resource Sharing (CORS) requests. This setting allows you to specify additional headers that can be accessed by the client-side JavaScript code in cross-origin requests.
Description
- Default value: Empty (no additional headers exposed)
- Possible values: Comma-separated list of header names
- Recommendations: Only expose headers that are necessary for your application's functionality and do not contain sensitive information.
This setting is part of Elasticsearch's CORS configuration. When set, it adds the specified headers to the Access-Control-Expose-Headers response header, allowing the client to read these headers from cross-origin requests.
Example
To expose the X-Custom-Header and Content-Length headers to cross-origin requests, you can use the cluster settings API:
PUT /_cluster/settings
{
"persistent": {
"http.cors.expose-headers": "X-Custom-Header,Content-Length"
}
}
You might want to change this setting if your application needs to access specific headers from cross-origin requests that are not exposed by default. For example, if you have custom headers that contain pagination information or request-specific metadata.
The effect of this change is that client-side JavaScript in a different origin will be able to read the specified headers from the Elasticsearch response.
Common Issues and Misuses
- Exposing too many headers, including sensitive ones, can lead to security vulnerabilities.
- Forgetting to enable CORS (
http.cors.enabled: true) when setting exposed headers. - Mistyping header names, which can result in headers not being exposed as expected.
Do's and Don'ts
- Do only expose headers that are necessary for your application's functionality.
- Do use lowercase for header names in the setting value.
- Don't expose headers that contain sensitive information.
- Don't use this setting without properly configuring other CORS-related settings.
- Do test your CORS configuration thoroughly after making changes.
Frequently Asked Questions
Q: How does http.cors.expose-headers relate to other CORS settings in Elasticsearch?
A: This setting works in conjunction with other CORS settings like http.cors.enabled and http.cors.allow-origin. While http.cors.enabled enables CORS support and http.cors.allow-origin specifies which origins are allowed to make cross-origin requests, http.cors.expose-headers determines which response headers are accessible to the client-side JavaScript.
Q: Can I use wildcards in the http.cors.expose-headers setting?
A: No, wildcards are not supported for this setting. You must explicitly list each header you want to expose.
Q: Are there any headers that are exposed by default without using this setting?
A: Yes, certain headers like Cache-Control, Content-Language, Content-Type, Expires, Last-Modified, and Pragma are considered "simple response headers" and are always exposed.
Q: How does exposing headers affect browser security?
A: Exposing headers allows client-side scripts from other origins to read those headers, which could potentially reveal sensitive information if not configured carefully. Always expose only the minimum necessary headers.
Q: Can I use http.cors.expose-headers to expose custom headers set by my application?
A: Yes, you can use this setting to expose custom headers that your Elasticsearch plugins or proxies might add to the response. Just ensure that these custom headers don't contain sensitive information.
