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Don't require Destination attribute in response when response is not signed #213

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merged 4 commits into from
Oct 29, 2019
Merged

Don't require Destination attribute in response when response is not signed #213

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624f63d
Destination is checked only if this is a signed SAML request, as that…
jasiek Sep 22, 2017
17cd2ec
clean up a bit
cvermilion Jul 11, 2019
f64703a
some test cleanup
cvermilion Jul 11, 2019
efa98f9
Check Destination when present, even if response unsigned
cvermilion Jul 12, 2019
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39 changes: 37 additions & 2 deletions service_provider.go
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Original file line number Diff line number Diff line change
Expand Up @@ -378,6 +378,40 @@ func (ivr *InvalidResponseError) Error() string {
return fmt.Sprintf("Authentication failed")
}

func responseIsSigned(response *etree.Document) (bool, error) {
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There was a comment here in #113 about whether this is correct when the response is encrypted (#113 (comment)).

As I read the SAML Core spec, individual parts of the response can be encrypted, but not the whole message. So if both a response signature and encryption are present, the signature should still sit outside any encrypted elements. In any case, it looks like this library only supports encrypted assertions.

signatureElement, err := findChild(response.Root(), "http://www.w3.org/2000/09/xmldsig#", "Signature")
if err != nil {
return false, err
}
return signatureElement != nil, nil
}

// validateDestination validates the Destination attribute.
// If the response is signed, the Destination is required to be present.
func (sp *ServiceProvider) validateDestination(response []byte, responseDom *Response) error {
responseXml := etree.NewDocument()
err := responseXml.ReadFromBytes(response)
if err != nil {
return err
}

signed, err := responseIsSigned(responseXml)
if err != nil {
return err
}


// Compare if the response is signed OR the Destination is provided.
// (Even if the response is not signed, if the Destination is set it must match.)
if signed || responseDom.Destination != "" {
if responseDom.Destination != sp.AcsURL.String() {
return fmt.Errorf("`Destination` does not match AcsURL (expected %q, actual %q)", sp.AcsURL.String(), responseDom.Destination)
}
}

return nil
}

// ParseResponse extracts the SAML IDP response received in req, validates
// it, and returns the verified attributes of the request.
//
Expand Down Expand Up @@ -409,8 +443,9 @@ func (sp *ServiceProvider) ParseResponse(req *http.Request, possibleRequestIDs [
retErr.PrivateErr = fmt.Errorf("cannot unmarshal response: %s", err)
return nil, retErr
}
if resp.Destination != sp.AcsURL.String() {
retErr.PrivateErr = fmt.Errorf("`Destination` does not match AcsURL (expected %q)", sp.AcsURL.String())

if err := sp.validateDestination(rawResponseBuf, &resp); err != nil {
retErr.PrivateErr = err
return nil, retErr
}

Expand Down
110 changes: 104 additions & 6 deletions service_provider_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@ import (

"crypto/x509"

"github.com/beevik/etree"
. "gopkg.in/check.v1"
)

Expand Down Expand Up @@ -642,6 +643,109 @@ func (test *ServiceProviderTest) TestCanParseResponse(c *C) {
})
}

func (test *ServiceProviderTest) replaceDestination(newDestination string) {
newStr := ""
if newDestination != "" {
newStr = `Destination="` + newDestination + `"`
}
test.SamlResponse = strings.Replace(test.SamlResponse, `Destination="https://15661444.ngrok.io/saml2/acs"`, newStr, 1)
}

func (test *ServiceProviderTest) TestCanProcessResponseWithoutDestination(c *C) {
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([]byte(test.IDPMetadata), &s.IDPMetadata)
c.Assert(err, IsNil)

req := http.Request{PostForm: url.Values{}}
test.replaceDestination("")
req.PostForm.Set("SAMLResponse", base64.StdEncoding.EncodeToString([]byte(test.SamlResponse)))
_, err = s.ParseResponse(&req, []string{"id-9e61753d64e928af5a7a341a97f420c9"})
c.Assert(err, Equals, nil)
}

func (test *ServiceProviderTest) responseDom() (doc *etree.Document) {
doc = etree.NewDocument()
doc.ReadFromString(test.SamlResponse)
return doc
}

func addSignatureToDocument(doc *etree.Document) *etree.Document {
responseEl := doc.FindElement("//Response")
signatureEl := doc.CreateElement("xmldsig:Signature")
signatureEl.CreateAttr("xmlns:xmldsig", "http://www.w3.org/2000/09/xmldsig#")
responseEl.AddChild(signatureEl)
return doc
}

func removeDestinationFromDocument(doc *etree.Document) *etree.Document {
responseEl := doc.FindElement("//Response")
responseEl.RemoveAttr("Destination")
return doc
}

func (test *ServiceProviderTest) TestMismatchedDestinationsWithSignaturePresent(c *C) {
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([]byte(test.IDPMetadata), &s.IDPMetadata)
c.Assert(err, IsNil)

req := http.Request{PostForm: url.Values{}}
test.replaceDestination("https://wrong/saml2/acs")
bytes, _ := addSignatureToDocument(test.responseDom()).WriteToBytes()
req.PostForm.Set("SAMLResponse", base64.StdEncoding.EncodeToString(bytes))
_, err = s.ParseResponse(&req, []string{"id-9e61753d64e928af5a7a341a97f420c9"})
c.Assert(err.(*InvalidResponseError).PrivateErr.Error(), Equals, "`Destination` does not match AcsURL (expected \"https://15661444.ngrok.io/saml2/acs\", actual \"https://wrong/saml2/acs\")")
}

func (test *ServiceProviderTest) TestMismatchedDestinationsWithNoSignaturePresent(c *C) {
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([]byte(test.IDPMetadata), &s.IDPMetadata)
c.Assert(err, IsNil)

req := http.Request{PostForm: url.Values{}}
test.replaceDestination("https://wrong/saml2/acs")
bytes, _ := test.responseDom().WriteToBytes()
req.PostForm.Set("SAMLResponse", base64.StdEncoding.EncodeToString(bytes))
_, err = s.ParseResponse(&req, []string{"id-9e61753d64e928af5a7a341a97f420c9"})
c.Assert(err.(*InvalidResponseError).PrivateErr.Error(), Equals, "`Destination` does not match AcsURL (expected \"https://15661444.ngrok.io/saml2/acs\", actual \"https://wrong/saml2/acs\")")
}

func (test *ServiceProviderTest) TestMissingDestinationWithSignaturePresent(c *C) {
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([]byte(test.IDPMetadata), &s.IDPMetadata)
c.Assert(err, IsNil)

req := http.Request{PostForm: url.Values{}}
test.replaceDestination("")
bytes, _ := addSignatureToDocument(test.responseDom()).WriteToBytes()
req.PostForm.Set("SAMLResponse", base64.StdEncoding.EncodeToString(bytes))
_, err = s.ParseResponse(&req, []string{"id-9e61753d64e928af5a7a341a97f420c9"})
c.Assert(err.(*InvalidResponseError).PrivateErr.Error(), Equals, "`Destination` does not match AcsURL (expected \"https://15661444.ngrok.io/saml2/acs\", actual \"\")")
}

func (test *ServiceProviderTest) TestInvalidResponses(c *C) {
s := ServiceProvider{
Key: test.Key,
Expand All @@ -662,12 +766,6 @@ func (test *ServiceProviderTest) TestInvalidResponses(c *C) {
_, err = s.ParseResponse(&req, []string{"id-9e61753d64e928af5a7a341a97f420c9"})
c.Assert(err.(*InvalidResponseError).PrivateErr, ErrorMatches, "cannot unmarshal response: expected element type <Response> but have <hello>")

s.AcsURL = mustParseURL("https://wrong/saml2/acs")
req.PostForm.Set("SAMLResponse", base64.StdEncoding.EncodeToString([]byte(test.SamlResponse)))
_, err = s.ParseResponse(&req, []string{"id-9e61753d64e928af5a7a341a97f420c9"})
c.Assert(err.(*InvalidResponseError).PrivateErr.Error(), Equals, "`Destination` does not match AcsURL (expected \"https://wrong/saml2/acs\")")
s.AcsURL = mustParseURL("https://15661444.ngrok.io/saml2/acs")

req.PostForm.Set("SAMLResponse", base64.StdEncoding.EncodeToString([]byte(test.SamlResponse)))
_, err = s.ParseResponse(&req, []string{"wrongRequestID"})
c.Assert(err.(*InvalidResponseError).PrivateErr.Error(), Equals, "`InResponseTo` does not match any of the possible request IDs (expected [wrongRequestID])")
Expand Down