CookieWithoutHttpOnly.qhelp

<!DOCTYPE qhelp PUBLIC
  "-//Semmle//qhelp//EN"
  "qhelp.dtd">
<qhelp>

<overview>
<p>Cookies without the <code>HttpOnly</code> flag set are accessible to client-side scripts such as JavaScript running in the same origin. 
In case of a Cross-Site Scripting (XSS) vulnerability, the cookie can be stolen by a malicious script.
If a sensitive cookie does not need to be accessed directly by client-side JS, the <code>HttpOnly</code> flag should be set.</p>
</overview>

<recommendation>
<p>
Set the <code>HttpOnly</code> flag to <code>true</code> for authentication cookies to ensure they are not accessible to client-side scripts.
</p> 
<p>
When using ASP.NET Core, <code>CookiePolicyOptions</code> can be used to set a default policy for cookies.

When using ASP.NET Web Forms, a default may also be configured in the <code>Web.config</code> file, using the <code>httpOnlyCookies</code> attribute of the 
the <code>&lt;httpCookies&gt;</code> element.
</p>
</recommendation>

<example>

<p>
In the example below, <code>Microsoft.AspNetCore.Http.CookieOptions.HttpOnly</code> is set to <code>true</code>.
</p>

<sample src="httponlyflagcore.cs" />

<p>
In the following example, <code>CookiePolicyOptions</code> are set programmatically to configure defaults.
</p>

<sample src="cookiepolicyoptions.cs" />

<p>
In the example below, <code>System.Web.HttpCookie.HttpOnly</code> is set to <code>true</code>.
</p>

<sample src="httponlyflag.cs" />

<p>
In the example below, the <code>httpOnlyCookies</code> attribute is set to <code>true</code> in the <code>Web.config</code> file.
</p>
<sample src="Web.config"/>

</example>

<references>

<li>ASP.Net Core docs: <a href="https://docs.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.http.cookieoptions.httponly">CookieOptions.HttpOnly Property</a>.</li>
<li>MDN: <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Set-Cookie">Set-Cookie</a> Header.</li>
<li>Web Forms docs: <a href="https://msdn.microsoft.com/en-us/library/system.web.httpcookie.httponly(v=vs.110).aspx">HttpCookie.HttpOnly Property</a>.</li>
<li>Web Forms docs: <a href="https://msdn.microsoft.com/library/ms228262%28v=vs.100%29.aspx">httpCookies Element</a>.</li>
<li>PortSwigger: <a href="https://portswigger.net/kb/issues/00500600_cookie-without-httponly-flag-set">Cookie without HttpOnly flag set</a></li>

</references>
</qhelp>