Impact With "trailingSlash: 'always'" configured, the "@astrojs/node" standalone server's static file handler appends a trailing slash to request paths and issues a "301" redirect. Paths beginning with "/" (slash-backslash) were not recognized as internal paths, so the handler would echo the raw path back in the "Location" header. Because browsers treat "" as "/" per the WHATWG URL specification, the resulting redirect could resolve to an external host. Preconditions: - "trailingSlash: 'always'" must be set (non-default; the default is "'ignore'") - The request path must not have a file extension in its final segment - An attacker must deliver the crafted link to a user Patches Fixed by treating backslash-prefixed paths the same as "//"-prefixed paths in "isInternalPath()", so they are no longer rewritten with a trailing slash. Workarounds Use the default "trailingSlash: 'ignore'" setting, which does not issue trailing-slash redirects in the static file handler. References - "WHATWG URL spec: backslash normalization" (https://url.spec.whatwg.org/#url-parsing)