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csrf: reject Origin: null as an opaque origin #207

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csrf: reject Origin: null as an opaque origin #207

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10 changes: 10 additions & 0 deletions csrf.go
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Original file line number Diff line number Diff line change
Expand Up @@ -279,6 +279,16 @@ func (cs *csrf) ServeHTTP(w http.ResponseWriter, r *http.Request) {
// if we have an Origin header, check it against our allowlist
origin := r.Header.Get("Origin")
if origin != "" {
// RFC 6454 §7.3: privacy-sensitive contexts (sandboxed iframes,
// some redirects, data: URLs) send the literal string "null".
// That's an opaque origin, never the same as ours and never
// something we'd put on the trusted list, so reject it up front
// instead of leaning on url.Parse returning a host-less URL.
if origin == "null" {
r = envError(r, ErrBadOrigin)
cs.opts.ErrorHandler.ServeHTTP(w, r)
return
}
parsedOrigin, err := url.Parse(origin)
if err != nil {
r = envError(r, ErrBadOrigin)
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8 changes: 8 additions & 0 deletions csrf_test.go
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Expand Up @@ -376,6 +376,7 @@ func TestProtectScenarios(t *testing.T) {
originUntrusted bool
originHTTP bool
originTrusted bool
originNull bool
secureRequest bool
refererTrusted bool
refererUntrusted bool
Expand Down Expand Up @@ -456,6 +457,11 @@ func TestProtectScenarios(t *testing.T) {
refererRelative: true,
tokenInvalid: true,
},
{
name: `cleartext POST with Origin "null" reject`,
originNull: true,
tokenValid: true,
},
}

for _, tt := range tests {
Expand Down Expand Up @@ -489,6 +495,8 @@ func TestProtectScenarios(t *testing.T) {
r.Header.Set("Origin", "https://www.gorillatoolkit.org")
case tt.originHTTP:
r.Header.Set("Origin", "http://www.gorillatoolkit.org")
case tt.originNull:
r.Header.Set("Origin", "null")
}

// Set the Referer header
Expand Down
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