[security] Authorization Bypass Through User-Controlled Key #489
Description
@emicklei - following on from #488 and https://huntr.dev/bounties/be837427-415c-4d8c-808b-62ce20aa84f1/, we are sharing the details of the report as requested in the SECURITY.md.
Authorization Bypass Through User-Controlled Key in emicklei/go-restful
Reported on Mar 7th 2022
Description
Hello go restful maintainer team, I would like to report a security concerning your CORS Filter feature.
Go restful allows user to specify a CORS Filter with a configurable AllowedDomains param - which is an array of domains allowed in CORS policy.
However, although there's is already another param called allowedOriginPatterns used for matching origin using regular expression, all domains in AllowedDomains is also used as regular expression to check for matching origin in this code in file cors_filter.go:
if len(c.allowedOriginPatterns) == 0 {
// compile allowed domains to allowed origin patterns
allowedOriginRegexps, err := compileRegexps(c.AllowedDomains)
if err != nil {
return false
}
c.allowedOriginPatterns = allowedOriginRegexps
}
for _, pattern := range c.allowedOriginPatterns {
if allowed = pattern.MatchString(origin); allowed {
break
}
}
So by this, if the user input example.com to be one of domain in AllowedDomains, all domains starting with example.com would be acceptable.
Proof of Concept
Install go restful and create a file main.go with this content:
package main
import (
restful "github.com/emicklei/go-restful/v3"
"io"
"net/http"
)
func main() {
container := restful.NewContainer()
ws := new(restful.WebService)
ws.Route(ws.GET("hello").To(hello))
container.Add(ws)
server := &http.Server{Addr: ":8000", Handler: container}
//container.Filter(logHeaders)
cors := restful.CrossOriginResourceSharing{
ExposeHeaders: []string{"X-My-Header"},
AllowedDomains: []string{"example.com"},
CookiesAllowed: true,
Container: container,
}
container.Filter(cors.Filter)
server.ListenAndServe()
}
func hello(req *restful.Request, resp *restful.Response) {
io.WriteString(resp, "world")
}
In the above code, example.com is configured as an allowed domain.
Run the above code and access link /hello with Origin Header = example.com.hacker.domain and see that the request gets through CORS policy and response looks like this:
HTTP/1.1 200 OK
Access-Control-Allow-Credentials: true
Access-Control-Allow-Origin: example.com.hacker.domain
Access-Control-Expose-Headers: X-My-Header
Date: Mon, 07 Mar 2022 13:31:08 GMT
Content-Length: 5
Content-Type: text/plain; charset=utf-8
Connection: close
world
Impact
This vulnerability is capable of breaking CORS policy and thus allowing any page to make requests, retrieve data on behalf of other users.