Summary
In affected versions, the HTTP Host request header was not validated before being used to reconstruct request.url. Because the routing algorithm relies on the raw HTTP path while request.url is rebuilt from the Host header, a malformed header could make request.url.path differ from the path that was actually requested. Middleware and endpoints that apply security restrictions based on request.url (rather than the raw scope path) could therefore be bypassed.
Details
When a client requests http://example.com/foo, it sends:
GET /foo HTTP/1.1
Host: example.com
Affected versions reconstructed the URL by concatenating http://{host}{path} and re-parsing the result. The Host value is only valid as a uri-host [ ":" port ] per RFC 9112 §3.2, where uri-host follows the restricted host grammar of RFC 3986 §3.2.2. When it contains characters outside that grammar - notably /, ?, or # - those characters move the path/query/fragment boundaries during re-parsing, so the parsed request.url.path no longer matches the path the server actually received. For example:
GET /foo HTTP/1.1
Host: example.com/abc?bar=
reconstructs to http://example.com/abc?bar=/foo, whose parsed path is /abc - even though routing used the real path /foo. The router still dispatches to /foo and the endpoint executes, but any middleware or code that reads request.url.path sees /abc, so path-based authorization checks can be bypassed.
Impact
Any application running an affected version that relies on request.url (or request.url.path) for security-sensitive decisions is affected. The most common case is middleware that gates access to certain path prefixes based on request.url.path. Deployments fronted by a proxy or load balancer are mitigated only if that proxy rejects or normalizes the malformed Host header before forwarding and the application does not trust attacker-controlled host headers (e.g. X-Forwarded-Host) elsewhere.
Mitigation
Upgrade to a patched version, which validates the Host header against the grammar of RFC 9112 §3.2 / RFC 3986 §3.2.2 when constructing request.url and falls back to scope["server"] for malformed values.
References
Summary
In affected versions, the HTTP
Hostrequest header was not validated before being used to reconstructrequest.url. Because the routing algorithm relies on the raw HTTP path whilerequest.urlis rebuilt from theHostheader, a malformed header could makerequest.url.pathdiffer from the path that was actually requested. Middleware and endpoints that apply security restrictions based onrequest.url(rather than the rawscopepath) could therefore be bypassed.Details
When a client requests
http://example.com/foo, it sends:Affected versions reconstructed the URL by concatenating
http://{host}{path}and re-parsing the result. TheHostvalue is only valid as auri-host [ ":" port ]per RFC 9112 §3.2, whereuri-hostfollows the restrictedhostgrammar of RFC 3986 §3.2.2. When it contains characters outside that grammar - notably/,?, or#- those characters move the path/query/fragment boundaries during re-parsing, so the parsedrequest.url.pathno longer matches the path the server actually received. For example:reconstructs to
http://example.com/abc?bar=/foo, whose parsedpathis/abc- even though routing used the real path/foo. The router still dispatches to/fooand the endpoint executes, but any middleware or code that readsrequest.url.pathsees/abc, so path-based authorization checks can be bypassed.Impact
Any application running an affected version that relies on
request.url(orrequest.url.path) for security-sensitive decisions is affected. The most common case is middleware that gates access to certain path prefixes based onrequest.url.path. Deployments fronted by a proxy or load balancer are mitigated only if that proxy rejects or normalizes the malformedHostheader before forwarding and the application does not trust attacker-controlled host headers (e.g.X-Forwarded-Host) elsewhere.Mitigation
Upgrade to a patched version, which validates the
Hostheader against the grammar of RFC 9112 §3.2 / RFC 3986 §3.2.2 when constructingrequest.urland falls back toscope["server"]for malformed values.References