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Require Destination on all SAML responses #660

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24 changes: 12 additions & 12 deletions service_provider.go
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Original file line number Diff line number Diff line change
Expand Up @@ -986,12 +986,8 @@ const (
// and properties are met.
func (sp *ServiceProvider) parseResponse(responseEl *etree.Element, possibleRequestIDs []string, now time.Time, signatureRequirement signatureRequirement, currentURL url.URL) (*Assertion, error) {
var responseSignatureErr error
var responseHasSignature bool
if signatureRequirement == signatureRequired {
responseSignatureErr = sp.validateSignature(responseEl)
if responseSignatureErr != errSignatureElementNotPresent {
responseHasSignature = true
}

// Note: we're deferring taking action on the signature validation until after we've
// processed the request attributes, because certain test cases seem to require this mis-feature.
Expand All @@ -1005,14 +1001,18 @@ func (sp *ServiceProvider) parseResponse(responseEl *etree.Element, possibleRequ
return nil, fmt.Errorf("cannot unmarshal response: %v", err)
}

// If the response is *not* signed, the Destination may be omitted.
if responseHasSignature || response.Destination != "" {
// Per section 3.4.5.2 of the SAML spec, Destination must match the location at which the response was received, i.e. currentURL.
// Historically, we checked against the SP's ACS URL instead of currentURL, which is usually the same but may differ in query params.
// To mitigate the risk of switching to comparing against currentURL, we still allow it if the ACS URL matches, even if the current URL doesn't.
if response.Destination != currentURL.String() && response.Destination != sp.AcsURL.String() {
return nil, fmt.Errorf("`Destination` does not match requested URL or AcsURL (destination %q, requested %q, acs %q)", response.Destination, currentURL.String(), sp.AcsURL.String())
}
// Per section 3.4.5.2 of the SAML spec, Destination MUST be present
// when a signature is present, and SHOULD be present otherwise. We
// require it always: for unsigned responses the Destination is the
// only non-cryptographic binding to this SP, and omitting it would
// let an attacker replay a response across service providers.
if response.Destination == "" {
return nil, fmt.Errorf("`Destination` is required but missing")
}
// Historically, we checked against the SP's ACS URL instead of currentURL, which is usually the same but may differ in query params.
// To mitigate the risk of switching to comparing against currentURL, we still allow it if the ACS URL matches, even if the current URL doesn't.
if response.Destination != currentURL.String() && response.Destination != sp.AcsURL.String() {
return nil, fmt.Errorf("`Destination` does not match requested URL or AcsURL (destination %q, requested %q, acs %q)", response.Destination, currentURL.String(), sp.AcsURL.String())
}

if err := sp.validateRequestID(response, possibleRequestIDs); err != nil {
Expand Down
40 changes: 37 additions & 3 deletions service_provider_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -946,7 +946,7 @@ func (test *ServiceProviderTest) replaceDestination(newDestination string) {
[]byte(`Destination="https://15661444.ngrok.io/saml2/acs"`), []byte(newStr), 1)
}

func TestSPCanProcessResponseWithoutDestination(t *testing.T) {
func TestSPRejectsResponseWithoutDestination(t *testing.T) {
test := NewServiceProviderTest(t)
s := ServiceProvider{
Key: test.Key,
Expand All @@ -962,7 +962,41 @@ func TestSPCanProcessResponseWithoutDestination(t *testing.T) {
test.replaceDestination("")
req.PostForm.Set("SAMLResponse", base64.StdEncoding.EncodeToString(test.SamlResponse))
_, err = s.ParseResponse(&req, []string{"id-9e61753d64e928af5a7a341a97f420c9"})
assert.Check(t, is.Error(err.(*InvalidResponseError).PrivateErr,
"`Destination` is required but missing"))
}

func TestSPRejectsUnsignedResponseWithoutDestination(t *testing.T) {
// Regression test for issue #12: On main, unsigned responses without
// Destination were silently accepted. The fix requires Destination always,
// because for unsigned responses it is the only binding to this SP.
test := NewServiceProviderTest(t)
s := ServiceProvider{
Key: test.Key,
Certificate: test.Certificate,
MetadataURL: mustParseURL("https://15661444.ngrok.io/saml2/metadata"),
AcsURL: mustParseURL("https://15661444.ngrok.io/saml2/acs"),
IDPMetadata: &EntityDescriptor{},
}
err := xml.Unmarshal(test.IDPMetadata, &s.IDPMetadata)
assert.Check(t, err)

// Build a minimal unsigned SAML response with no Destination attribute.
// This simulates an IdP sending a response without any audience binding.
unsignedResp := `<saml2p:Response xmlns:saml2p="urn:oasis:names:tc:SAML:2.0:protocol"` +
` ID="_test123" InResponseTo="id-9e61753d64e928af5a7a341a97f420c9"` +
` IssueInstant="2015-12-01T01:56:21.375Z" Version="2.0">` +
`<saml2:Issuer xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion"` +
` Format="urn:oasis:names:tc:SAML:2.0:nameid-format:entity">` +
`https://idp.testshib.org/idp/shibboleth</saml2:Issuer>` +
`<saml2p:Status><saml2p:StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:Success"/></saml2p:Status>` +
`</saml2p:Response>`

req := http.Request{PostForm: url.Values{}, URL: &s.AcsURL}
req.PostForm.Set("SAMLResponse", base64.StdEncoding.EncodeToString([]byte(unsignedResp)))
_, err = s.ParseResponse(&req, []string{"id-9e61753d64e928af5a7a341a97f420c9"})
assert.Check(t, is.Error(err.(*InvalidResponseError).PrivateErr,
"`Destination` is required but missing"))
}

func (test *ServiceProviderTest) responseDom(t *testing.T) (doc *etree.Document) {
Expand Down Expand Up @@ -1079,7 +1113,7 @@ func TestServiceProviderMissingDestinationWithSignaturePresent(t *testing.T) {
req.PostForm.Set("SAMLResponse", base64.StdEncoding.EncodeToString(bytes))
_, err = s.ParseResponse(&req, []string{"id-9e61753d64e928af5a7a341a97f420c9"})
assert.Check(t, is.Error(err.(*InvalidResponseError).PrivateErr,
"`Destination` does not match requested URL or AcsURL (destination \"\", requested \"https://15661444.ngrok.io/saml2/acs\", acs \"https://15661444.ngrok.io/saml2/acs\")"))
"`Destination` is required but missing"))
}

func TestSPMismatchedDestinationsWithSignaturePresent(t *testing.T) {
Expand Down Expand Up @@ -1142,7 +1176,7 @@ func TestSPMissingDestinationWithSignaturePresent(t *testing.T) {
req.PostForm.Set("SAMLResponse", base64.StdEncoding.EncodeToString(bytes))
_, err = s.ParseResponse(&req, []string{"id-9e61753d64e928af5a7a341a97f420c9"})
assert.Check(t, is.Error(err.(*InvalidResponseError).PrivateErr,
"`Destination` does not match requested URL or AcsURL (destination \"\", requested \"https://15661444.ngrok.io/saml2/acs\", acs \"https://15661444.ngrok.io/saml2/acs\")"))
"`Destination` is required but missing"))
}

func TestSPInvalidAssertions(t *testing.T) {
Expand Down