@astrojs/node: Backslash-prefixed paths not recognized as internal by trailing-slash redirect

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