When a cookie is protected with the secure attribute set to true it will not be send by the browser over an unencrypted HTTP request and thus cannot be observed by an unauthorized person during a man-in-the-middle attack.

Why is this an issue?

When a cookie is created without the secure attribute set to true, browsers will transmit it over unencrypted HTTP connections as well as HTTPS. An attacker who can observe or intercept network traffic—for example on a public Wi-Fi network—can read the cookie value in cleartext.

What is the potential impact?

Session hijacking

If a session cookie is transmitted over an unencrypted HTTP connection, an attacker who can intercept the traffic can steal it. With a valid session cookie, the attacker can impersonate the victim and gain full access to their account without knowing their password. Even on sites that primarily use HTTPS, a single HTTP request containing the session cookie is enough to expose it.

How to fix it in Core PHP

Set the secure parameter to true when creating cookies to prevent them from being transmitted over unencrypted HTTP connections.

Code examples

Noncompliant code example

In php.ini you can specify the flags for the session cookie which is security-sensitive:

session.cookie_secure = 0; // Noncompliant

Same thing in PHP code:

session_set_cookie_params($lifetime, $path, $domain, false);  // Noncompliant: this security-sensitive session cookie is created with the secure flag (the fourth argument) set to _false_

If you create a custom security-sensitive cookie in your PHP code:

$value = "sensitive data";
setcookie($name, $value, $expire, $path, $domain, false);  // Noncompliant: a security-sensitive cookie is created with the secure flag  (the sixth argument) set to _false_

Compliant solution

session.cookie_secure = 1;

session_set_cookie_params($lifetime, $path, $domain, true);

$value = "sensitive data";
setcookie($name, $value, $expire, $path, $domain, true);

Resources

Standards