Title: Cannot modify header!
Last modified: May 4, 2024

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# Cannot modify header!

 *  Resolved [tonygao](https://wordpress.org/support/users/tonygao/)
 * (@tonygao)
 * [2 years ago](https://wordpress.org/support/topic/cannot-modify-header-15/)
 * [PHP Warning: Cannot modify header information – headers already sent in /public_html/
   wp-content/plugins/wordfence/vendor/wordfence/wf-waf/src/lib/waf.php on line 
   1195
 * 
   PHP Warning: Cannot modify header information – headers already sent in /public_html/
   wp-content/plugins/wordfence/vendor/wordfence/wf-waf/src/lib/utils.php on line
   749
 * PHP Warning: Cannot modify header information – headers already sent in /public_html/
   wp-content/plugins/wordfence/vendor/wordfence/wf-waf/src/lib/utils.php on line
   750
 * PHP Warning: Cannot modify header information – headers already sent in /public_html/
   wp-content/plugins/wordfence/vendor/wordfence/wf-waf/src/lib/utils.php on line
   751

Viewing 2 replies - 1 through 2 (of 2 total)

 *  [Jane](https://wordpress.org/support/users/jstepak/)
 * (@jstepak)
 * [2 years ago](https://wordpress.org/support/topic/cannot-modify-header-15/#post-17733673)
 * We’re getting these warning messages, too. Following this thread.
 *  Plugin Support [wfmargaret](https://wordpress.org/support/users/wfmargaret/)
 * (@wfmargaret)
 * [2 years ago](https://wordpress.org/support/topic/cannot-modify-header-15/#post-17736101)
 * Hi [@tonygao](https://wordpress.org/support/users/tonygao/),
 * The “Cannot modify header information – headers already sent by” error message
   typically indicates that something in your PHP code has caused output to be sent
   before the HTTP headers are fully defined. It’s been linked to another plugin
   loading WordPress core files out of order in the past, which is a possibility
   here.
 * To rule out a plugin or theme conflict, try to run Wordfence as your only enabled
   plugin and revert to a default theme such as Twenty Twenty-Four. If you no longer
   see the error, re-enable your plugins and theme one-by-one until it recurs again
   to help find the cause.
 * Thanks,
   Margaret

Viewing 2 replies - 1 through 2 (of 2 total)

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## Tags

 * [Cannot modify header information](https://wordpress.org/support/topic-tag/cannot-modify-header-information/)
 * [PHP Warning](https://wordpress.org/support/topic-tag/php-warning/)

 * 2 replies
 * 3 participants
 * Last reply from: [wfmargaret](https://wordpress.org/support/users/wfmargaret/)
 * Last activity: [2 years ago](https://wordpress.org/support/topic/cannot-modify-header-15/#post-17736101)
 * Status: resolved