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X-XSS-Protection

The HTTP X-XSS-Protection response header is a feature of Internet Explorer, Chrome and Safari that stops pages from loading when they detect reflected cross-site scripting (XSS) attacks. Although these protections are largely unnecessary in modern browsers when sites implement a strong Content-Security-Policy that disables the use of inline JavaScript ('unsafe-inline'), they can still provide protections for users of older web browsers that don't yet support CSP.

Header type Response header
Forbidden header name no

Syntax

X-XSS-Protection: 0
X-XSS-Protection: 1
X-XSS-Protection: 1; mode=block
X-XSS-Protection: 1; report=<reporting-uri>
0
Disables XSS filtering.
1
Enables XSS filtering (usually default in browsers). If a cross-site scripting attack is detected, the browser will sanitize the page (remove the unsafe parts).
1;mode=block
Enables XSS filtering. Rather than sanitizing the page, the browser will prevent rendering of the page if an attack is detected.
1; report=<reporting-URI> (Chromium only)
Enables XSS filtering. If a cross-site scripting attack is detected, the browser will sanitize the page and report the violation. This uses the functionality of the CSP report-uri directive to send a report.

Example

Block pages from loading when they detect reflected XSS attacks:

X-XSS-Protection: 1;mode=block

PHP

header("X-XSS-Protection: 1; mode=block");

Apache (.htaccess)

<IfModule mod_headers.c> 
  Header set X-XSS-Protection "1; mode=block" 
</IfModule>

Specifications

Not part of any specifications or drafts.

Browser compatibility

Feature Chrome Edge Firefox Internet Explorer Opera Safari Servo
X-XSS-Protection (Yes) (Yes) No support 8.0 (Yes) (Yes) No support
Feature Android Chrome for Android Edge Mobile Firefox for Android IE Mobile Opera Mobile Safari Mobile
X-XSS-Protection (Yes) (Yes) (Yes) No support ? (Yes) (Yes)

See also

© 2005–2017 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-XSS-Protection