A vulnerability in @sveltejs/adapter-node causes the server to crash when proxying certain requests via fetch due to attempts to add headers to immutable requests. This results in a denial of service for other requests handled by the server. The issue affects versions >=5.5.7 <5.5.8 and >=6.0.0-next.0 <6.0.1 and has been fixed in versions 5.5.8 and 6.0.1.