https://www.thaddeuskoenig.com/tags/javascript/Recent content in Javascript on Thaddeus KoenigHugoen-US© 2026 Thaddeus KoenigFri, 16 Jan 2026 16:47:57 -0500https://www.thaddeuskoenig.com/blog/20260116/Fri, 16 Jan 2026 15:50:00 -0500https://www.thaddeuskoenig.com/blog/20260116/<h2 id="intro">Intro<a href="#intro" class="post-heading__anchor" aria-hidden="true">#</a> </h2> <p>Today while messing around with one of the HackTheBox retired machines &ldquo;Previous&rdquo;, the method of gaining initial access is due to the &ldquo;Middleware&rdquo; Authentication Bypass in Next.js. This vulnerability can be exploited to bypass authorization and access sensitive pages. Details of the affected versions can be found here <a href="https://www.cve.org/CVERecord?id=CVE-2025-29927" class="link--external" target="_blank" rel="noreferrer" >CVE-2025-29927</a>.</p> <h2 id="background">Background<a href="#background" class="post-heading__anchor" aria-hidden="true">#</a> </h2> <p>The CVE is a vulnerability in the handling of &ldquo;middleware&rdquo;. In its simplest terms (the only ones I understand) middleware is a function used to process a user request in some form or fashion. This could be as simple as parsing raw data into a JSON template, or as much as providing authentication to an application that doesn&rsquo;t have any. In the case of the HackTheBox machine, this was the case. The application uses <a href="https://next-auth.js.org/" class="link--external" target="_blank" rel="noreferrer" >Next Auth</a> as its authentication provider. In an incredibly oversimplified piece of pseudocode, authentication in this application looks like this (forgive me im not a javascipt developer).</p>