@fastify/session is a session plugin for fastify. Requires the @fastify/cookie plugin. When restoring the cookie from the session store, the expires field is overriden if the maxAge field was set.
This means a cookie is never correctly detected as expired and thus expired sessions are not destroyed. This vulnerability has been patched 10.8.0.
According to WASC, “Insufficient Session Expiration is when a web site permits an attacker to reuse old session credentials or session IDs for authorization.”