Prevent redirect to Host (2) (#19175)

Unhelpfully Locations starting with `/\` will be converted by the
browser to `//` because ... well I do not fully understand. Certainly
the RFCs and MDN do not indicate that this would be expected. Providing
"compatibility" with the (mis)behaviour of a certain proprietary OS is
my suspicion. However, we clearly have to protect against this.

Therefore we should reject redirection locations that match the regular
expression: `^/[\\\\/]+`

Reference #9678

Signed-off-by: Andrew Thornton <art27@cantab.net>

diff --git a/modules/context/context.go b/modules/context/context.go
index 61f58eabb22012822919c50ed26ae187c637188b..6cd503984f54639c933d34b0d0753dd19716ee69 100644 (file)
--- a/modules/context/context.go
+++ b/modules/context/context.go
@@ -181,6 +181,12 @@ func (ctx *Context) RedirectToFirst(location ...string) {
                        continue
                }
 
+               // Unfortunately browsers consider a redirect Location with preceding "//" and "/\" as meaning redirect to "http(s)://REST_OF_PATH"
+               // Therefore we should ignore these redirect locations to prevent open redirects
+               if len(loc) > 1 && loc[0] == '/' && (loc[1] == '/' || loc[1] == '\\') {
+                       continue
+               }
+
                u, err := url.Parse(loc)
                if err != nil || ((u.Scheme != "" || u.Host != "") && !strings.HasPrefix(strings.ToLower(loc), strings.ToLower(setting.AppURL))) {
                        continue