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connector/saml: clean up SAML verification logic and comments

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This commit is contained in:
Eric Chiang 2017-04-06 17:11:28 -07:00
parent 258ec4ff4b
commit 362e0798a4
3 changed files with 195 additions and 269 deletions
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234
connector/saml/saml.go
View File

@ -2,10 +2,8 @@
package saml
import (
"crypto/rand"
"crypto/x509"
"encoding/base64"
"encoding/hex"
"encoding/pem"
"encoding/xml"
"errors"
@ -270,12 +268,22 @@ func (p *provider) POSTData(s connector.Scopes, id string) (action, value string
return p.ssoURL, base64.StdEncoding.EncodeToString(data), nil
}
// HandlePOST interprets a request from a SAML provider attempting to verify a
// user's identity.
//
// The steps taken are:
//
// * Verify signature on XML document (or verify sig on assertion elements).
// * Verify various parts of the Assertion element. Conditions, audience, etc.
// * Map the Assertion's attribute elements to user info.
//
func (p *provider) HandlePOST(s connector.Scopes, samlResponse, inResponseTo string) (ident connector.Identity, err error) {
rawResp, err := base64.StdEncoding.DecodeString(samlResponse)
if err != nil {
return ident, fmt.Errorf("decode response: %v", err)
}
// Root element is allowed to not be signed if the Assertion element is.
rootElementSigned := true
if p.validator != nil {
rawResp, rootElementSigned, err = verifyResponseSig(p.validator, rawResp)
@ -289,6 +297,8 @@ func (p *provider) HandlePOST(s connector.Scopes, samlResponse, inResponseTo str
return ident, fmt.Errorf("unmarshal response: %v", err)
}
// If the root element isn't signed, there's no reason to inspect these
// elements. They're not verified.
if rootElementSigned {
if p.ssoIssuer != "" && resp.Issuer != nil && resp.Issuer.Issuer != p.ssoIssuer {
return ident, fmt.Errorf("expected Issuer value %s, got %s", p.ssoIssuer, resp.Issuer.Issuer)
@ -303,10 +313,14 @@ func (p *provider) HandlePOST(s connector.Scopes, samlResponse, inResponseTo str
// Destination is optional.
if resp.Destination != "" && resp.Destination != p.redirectURI {
return ident, fmt.Errorf("expected destination %q got %q", p.redirectURI, resp.Destination)
}
if err = p.validateStatus(&resp); err != nil {
// Status is a required element.
if resp.Status == nil {
return ident, fmt.Errorf("Response did not contain a Status element")
}
if err = p.validateStatus(resp.Status); err != nil {
return ident, err
}
}
@ -315,17 +329,26 @@ func (p *provider) HandlePOST(s connector.Scopes, samlResponse, inResponseTo str
if assertion == nil {
return ident, fmt.Errorf("response did not contain an assertion")
}
// Subject is usually optional, but we need it for the user ID, so complain
// if it's not present.
subject := assertion.Subject
if subject == nil {
return ident, fmt.Errorf("response did not contain a subject")
}
if err = p.validateConditions(assertion); err != nil {
// Validate that the response is to the request we originally sent.
if err = p.validateSubject(subject, inResponseTo); err != nil {
return ident, err
}
if err = p.validateSubjectConfirmation(subject); err != nil {
// Conditions element is optional, but must be validated if present.
if assertion.Conditions != nil {
// Validate that dex is the intended audience of this response.
if err = p.validateConditions(assertion.Conditions); err != nil {
return ident, err
}
}
switch {
case subject.NameID != nil:
@ -336,21 +359,31 @@ func (p *provider) HandlePOST(s connector.Scopes, samlResponse, inResponseTo str
return ident, fmt.Errorf("subject does not contain an NameID element")
}
// After verifying the assertion, map data in the attribute statements to
// various user info.
attributes := assertion.AttributeStatement
if attributes == nil {
return ident, fmt.Errorf("response did not contain a AttributeStatement")
}
// Grab the email.
if ident.Email, _ = attributes.get(p.emailAttr); ident.Email == "" {
return ident, fmt.Errorf("no attribute with name %q: %s", p.emailAttr, attributes.names())
}
// TODO(ericchiang): Does SAML have an email_verified equivalent?
ident.EmailVerified = true
// Grab the username.
if ident.Username, _ = attributes.get(p.usernameAttr); ident.Username == "" {
return ident, fmt.Errorf("no attribute with name %q: %s", p.usernameAttr, attributes.names())
}
if s.Groups && p.groupsAttr != "" {
if !s.Groups || p.groupsAttr == "" {
// Groups not requested or not configured. We're done.
return ident, nil
}
// Grab the groups.
if p.groupsDelim != "" {
groupsStr, ok := attributes.get(p.groupsAttr)
if !ok {
@ -365,24 +398,18 @@ func (p *provider) HandlePOST(s connector.Scopes, samlResponse, inResponseTo str
}
ident.Groups = groups
}
}
return ident, nil
}
// Validate that the StatusCode of the Response is success.
// Otherwise return a human readable message to the end user
func (p *provider) validateStatus(resp *response) error {
// Status is mandatory in the Response type
status := resp.Status
if status == nil {
return fmt.Errorf("response did not contain a Status")
}
// validateStatus verifies that the response has a good status code or
// formats a human readble error based on the bad status.
func (p *provider) validateStatus(status *status) error {
// StatusCode is mandatory in the Status type
statusCode := status.StatusCode
if statusCode == nil {
return fmt.Errorf("response did not contain a StatusCode")
}
if statusCode.Value != statusCodeSuccess {
parts := strings.Split(statusCode.Value, ":")
lastPart := parts[len(parts)-1]
@ -396,96 +423,107 @@ func (p *provider) validateStatus(resp *response) error {
return nil
}
// Multiple subject SubjectConfirmation can be in the assertion
// and at least one SubjectConfirmation must be valid.
// validateSubject ensures the response is to the request we expect.
//
// This is described in the spec "Profiles for the OASIS Security
// Assertion Markup Language" in section 3.3 Bearer.
// see https://www.oasis-open.org/committees/download.php/35389/sstc-saml-profiles-errata-2.0-wd-06-diff.pdf
func (p *provider) validateSubjectConfirmation(subject *subject) error {
validSubjectConfirmation := false
subjectConfirmations := subject.SubjectConfirmations
if subjectConfirmations != nil && len(subjectConfirmations) > 0 {
for _, subjectConfirmation := range subjectConfirmations {
// skip if method is wrong
method := subjectConfirmation.Method
if method != "" && method != subjectConfirmationMethodBearer {
continue
}
subjectConfirmationData := subjectConfirmation.SubjectConfirmationData
if subjectConfirmationData == nil {
continue
}
inResponseTo := subjectConfirmationData.InResponseTo
if inResponseTo != "" {
// TODO also validate InResponseTo if present
}
// only validate that subjectConfirmationData is not expired
now := p.now()
notOnOrAfter := time.Time(subjectConfirmationData.NotOnOrAfter)
if !notOnOrAfter.IsZero() {
if now.After(notOnOrAfter) {
continue
}
}
// validate recipient if present
recipient := subjectConfirmationData.Recipient
if recipient != "" && recipient != p.redirectURI {
continue
}
validSubjectConfirmation = true
}
}
if !validSubjectConfirmation {
return fmt.Errorf("no valid SubjectConfirmation was found on this Response")
}
return nil
//
// Some of these fields are optional, but we're going to be strict here since
// we have no other way of guarenteeing that this is actually the response to
// the request we expect.
func (p *provider) validateSubject(subject *subject, inResponseTo string) error {
// Optional according to the spec, but again, we're going to be strict here.
if len(subject.SubjectConfirmations) == 0 {
return fmt.Errorf("Subject contained no SubjectConfrimations")
}
// Validates the Conditions element and all of it's content
var errs []error
// One of these must match our assumptions, not all.
for _, c := range subject.SubjectConfirmations {
err := func() error {
if c.Method != subjectConfirmationMethodBearer {
return fmt.Errorf("unexpected subject confirmation method: %v", c.Method)
}
data := c.SubjectConfirmationData
if data == nil {
return fmt.Errorf("SubjectConfirmation contained no SubjectConfirmationData")
}
if data.InResponseTo != inResponseTo {
return fmt.Errorf("expected SubjectConfirmationData InResponseTo value %q, got %q", inResponseTo, data.InResponseTo)
}
notBefore := time.Time(data.NotBefore)
notOnOrAfter := time.Time(data.NotOnOrAfter)
now := p.now()
if !notBefore.IsZero() && before(now, notBefore) {
return fmt.Errorf("at %s got response that cannot be processed before %s", now, notBefore)
}
if !notOnOrAfter.IsZero() && after(now, notOnOrAfter) {
return fmt.Errorf("at %s got response that cannot be processed because it expired at %s", now, notOnOrAfter)
}
if r := data.Recipient; r != "" && r != p.redirectURI {
return fmt.Errorf("expected Recipient %q got %q", p.redirectURI, r)
}
return nil
}()
if err == nil {
// Subject is valid.
return nil
}
errs = append(errs, err)
}
if len(errs) == 1 {
return fmt.Errorf("failed to validate subject confirmation: %v", errs[0])
}
return fmt.Errorf("failed to validate subject confirmation: %v", errs)
}
// validationConditions ensures that dex is the intended audience
// for the request, and not another service provider.
//
// See: https://docs.oasis-open.org/security/saml/v2.0/saml-core-2.0-os.pdf
// "2.3.3 Element <Assertion>"
func (p *provider) validateConditions(assertion *assertion) error {
// Checks if a Conditions element exists
conditions := assertion.Conditions
if conditions == nil {
return nil
}
// Validates Assertion timestamps
func (p *provider) validateConditions(conditions *conditions) error {
// Ensure the conditions haven't expired.
now := p.now()
notBefore := time.Time(conditions.NotBefore)
if !notBefore.IsZero() {
if now.Add(allowedClockDrift).Before(notBefore) {
if !notBefore.IsZero() && before(now, notBefore) {
return fmt.Errorf("at %s got response that cannot be processed before %s", now, notBefore)
}
}
notOnOrAfter := time.Time(conditions.NotOnOrAfter)
if !notOnOrAfter.IsZero() {
if now.After(notOnOrAfter.Add(allowedClockDrift)) {
if !notOnOrAfter.IsZero() && after(now, notOnOrAfter) {
return fmt.Errorf("at %s got response that cannot be processed because it expired at %s", now, notOnOrAfter)
}
// Sometimes, dex's issuer string can be different than the redirect URI,
// but if dex's issuer isn't explicitly provided assume the redirect URI.
expAud := p.entityIssuer
if expAud == "" {
expAud = p.redirectURI
}
// Validates audience
audienceValue := p.entityIssuer
if audienceValue == "" {
audienceValue = p.redirectURI
}
audienceRestriction := conditions.AudienceRestriction
if audienceRestriction != nil {
audiences := audienceRestriction.Audiences
if audiences != nil && len(audiences) > 0 {
values := make([]string, len(audiences))
// AudienceRestriction elements indicate the intended audience(s) of an
// assertion. If dex isn't in these audiences, reject the assertion.
//
// Note that if there are multiple AudienceRestriction elements, each must
// individually contain dex in their audience list.
for _, r := range conditions.AudienceRestriction {
values := make([]string, len(r.Audiences))
issuerInAudiences := false
for i, audience := range audiences {
if audience.Value == audienceValue {
for i, aud := range r.Audiences {
if aud.Value == expAud {
issuerInAudiences = true
break
}
values[i] = audience.Value
values[i] = aud.Value
}
if !issuerInAudiences {
return fmt.Errorf("required audience %s was not in Response audiences %s", audienceValue, values)
}
return fmt.Errorf("required audience %s was not in Response audiences %s", expAud, values)
}
}
return nil
@ -544,24 +582,14 @@ func verifyResponseSig(validator *dsig.ValidationContext, data []byte) (signed [
return signed, false, err
}
func uuidv4() string {
u := make([]byte, 16)
if _, err := rand.Read(u); err != nil {
panic(err)
// before determines if a given time is before the current time, with an
// allowed clock drift.
func before(now, notBefore time.Time) bool {
return now.Add(allowedClockDrift).Before(notBefore)
}
u[6] = (u[6] | 0x40) & 0x4F
u[8] = (u[8] | 0x80) & 0xBF
r := make([]byte, 36)
r[8] = '-'
r[13] = '-'
r[18] = '-'
r[23] = '-'
hex.Encode(r, u[0:4])
hex.Encode(r[9:], u[4:6])
hex.Encode(r[14:], u[6:8])
hex.Encode(r[19:], u[8:10])
hex.Encode(r[24:], u[10:])
return string(r)
// after determines if a given time is after the current time, with an
// allowed clock drift.
func after(now, notOnOrAfter time.Time) bool {
return now.After(notOnOrAfter.Add(allowedClockDrift))
}

197
connector/saml/saml_test.go
View File

@ -7,7 +7,6 @@ import (
"errors"
"io/ioutil"
"sort"
"strings"
"testing"
"time"
@ -47,6 +46,7 @@ type responseTest struct {
now string
inResponseTo string
redirectURI string
entityIssuer string
// Attribute customization.
usernameAttr string
@ -196,6 +196,51 @@ func TestAssertionSignedNotResponse(t *testing.T) {
test.run(t)
}
func TestInvalidSubjectInResponseTo(t *testing.T) {
test := responseTest{
caFile: "testdata/ca.crt",
respFile: "testdata/assertion-signed.xml",
now: "2017-04-04T04:34:59.330Z",
usernameAttr: "Name",
emailAttr: "email",
inResponseTo: "invalid-id", // Bad InResponseTo value.
redirectURI: "http://127.0.0.1:5556/dex/callback",
wantErr: true,
}
test.run(t)
}
func TestInvalidSubjectRecipient(t *testing.T) {
test := responseTest{
caFile: "testdata/ca.crt",
respFile: "testdata/assertion-signed.xml",
now: "2017-04-04T04:34:59.330Z",
usernameAttr: "Name",
emailAttr: "email",
inResponseTo: "6zmm5mguyebwvajyf2sdwwcw6m",
redirectURI: "http://bad.com/dex/callback", // Doesn't match Recipient value.
wantErr: true,
}
test.run(t)
}
func TestInvalidAssertionAudience(t *testing.T) {
test := responseTest{
caFile: "testdata/ca.crt",
respFile: "testdata/assertion-signed.xml",
now: "2017-04-04T04:34:59.330Z",
usernameAttr: "Name",
emailAttr: "email",
inResponseTo: "6zmm5mguyebwvajyf2sdwwcw6m",
redirectURI: "http://127.0.0.1:5556/dex/callback",
// EntityIssuer overrides RedirectURI when determining the expected
// audience. In this case, ensure the audience is invalid.
entityIssuer: "http://localhost:5556/dex/callback",
wantErr: true,
}
test.run(t)
}
// TestTwoAssertionFirstSigned tries to catch an edge case where an attacker
// provides a second assertion that's not signed.
func TestTwoAssertionFirstSigned(t *testing.T) {
@ -236,6 +281,7 @@ func (r responseTest) run(t *testing.T) {
EmailAttr: r.emailAttr,
GroupsAttr: r.groupsAttr,
RedirectURI: r.redirectURI,
EntityIssuer: r.entityIssuer,
// Never logging in, don't need this.
SSOURL: "http://foo.bar/",
}
@ -355,152 +401,3 @@ func TestVerifySignedMessageAndSignedAssertion(t *testing.T) {
func TestVerifyUnsignedMessageAndUnsignedAssertion(t *testing.T) {
runVerify(t, "testdata/idp-cert.pem", "testdata/idp-resp.xml", false)
}
func TestValidateStatus(t *testing.T) {
p := newProvider("", "")
var err error
resp := response{}
// Test missing Status element
err = p.validateStatus(&resp)
if err == nil || !strings.HasSuffix(err.Error(), `Status`) {
t.Fatalf("validation should fail with missing Status")
}
// Test missing StatusCode element
resp.Status = &status{}
err = p.validateStatus(&resp)
if err == nil || !strings.HasSuffix(err.Error(), `StatusCode`) {
t.Fatalf("validation should fail with missing StatusCode")
}
// Test failed request without StatusMessage
resp.Status.StatusCode = &statusCode{
Value: ":Requester",
}
err = p.validateStatus(&resp)
if err == nil || !strings.HasSuffix(err.Error(), `"Requester"`) {
t.Fatalf("validation should fail with code %q", "Requester")
}
// Test failed request with StatusMessage
resp.Status.StatusMessage = &statusMessage{
Value: "Failed",
}
err = p.validateStatus(&resp)
if err == nil || !strings.HasSuffix(err.Error(), `"Requester" -> Failed`) {
t.Fatalf("validation should fail with code %q and message %q", "Requester", "Failed")
}
}
func TestValidateSubjectConfirmation(t *testing.T) {
p := newProvider("", "")
var err error
var notAfter time.Time
subj := &subject{}
// Subject without any SubjectConfirmation
err = p.validateSubjectConfirmation(subj)
if err == nil {
t.Fatalf("validation of %q should fail", "Subject without any SubjectConfirmation")
}
// SubjectConfirmation without Method and SubjectConfirmationData
subj.SubjectConfirmations = []subjectConfirmation{subjectConfirmation{}}
err = p.validateSubjectConfirmation(subj)
if err == nil {
t.Fatalf("validation of %q should fail", "SubjectConfirmation without Method and SubjectConfirmationData")
}
// SubjectConfirmation with invalid Method and no SubjectConfirmationData
subj.SubjectConfirmations = []subjectConfirmation{subjectConfirmation{
Method: "invalid",
}}
err = p.validateSubjectConfirmation(subj)
if err == nil {
t.Fatalf("validation of %q should fail", "SubjectConfirmation with invalid Method and no SubjectConfirmationData")
}
// SubjectConfirmation with valid Method and empty SubjectConfirmationData
subjConfirmationData := subjectConfirmationData{}
subj.SubjectConfirmations = []subjectConfirmation{subjectConfirmation{
Method: "urn:oasis:names:tc:SAML:2.0:cm:bearer",
SubjectConfirmationData: &subjConfirmationData,
}}
err = p.validateSubjectConfirmation(subj)
if err != nil {
t.Fatalf("validation of %q should succeed", "SubjectConfirmation with valid Method and empty SubjectConfirmationData")
}
// SubjectConfirmationData with invalid Recipient
subjConfirmationData.Recipient = "invalid"
err = p.validateSubjectConfirmation(subj)
if err == nil {
t.Fatalf("validation of %q should fail", "SubjectConfirmationData with invalid Recipient")
}
// expired SubjectConfirmationData
notAfter = p.now().Add(-time.Duration(60) * time.Second)
subjConfirmationData.NotOnOrAfter = xmlTime(notAfter)
subjConfirmationData.Recipient = defaultRedirectURI
err = p.validateSubjectConfirmation(subj)
if err == nil {
t.Fatalf("validation of %q should fail", " expired SubjectConfirmationData")
}
// valid SubjectConfirmationData
notAfter = p.now().Add(+time.Duration(60) * time.Second)
subjConfirmationData.NotOnOrAfter = xmlTime(notAfter)
subjConfirmationData.Recipient = defaultRedirectURI
err = p.validateSubjectConfirmation(subj)
if err != nil {
t.Fatalf("validation of %q should succed", "valid SubjectConfirmationData")
}
}
func TestValidateConditions(t *testing.T) {
p := newProvider("", "")
var err error
var notAfter, notBefore time.Time
cond := conditions{
AudienceRestriction: &audienceRestriction{},
}
assert := &assertion{}
// Assertion without Conditions
err = p.validateConditions(assert)
if err != nil {
t.Fatalf("validation of %q should succeed", "Assertion without Conditions")
}
// Assertion with empty Conditions
assert.Conditions = &cond
err = p.validateConditions(assert)
if err != nil {
t.Fatalf("validation of %q should succeed", "Assertion with empty Conditions")
}
// Conditions with valid timestamps
notBefore = p.now().Add(-time.Duration(60) * time.Second)
notAfter = p.now().Add(+time.Duration(60) * time.Second)
cond.NotBefore = xmlTime(notBefore)
cond.NotOnOrAfter = xmlTime(notAfter)
err = p.validateConditions(assert)
if err != nil {
t.Fatalf("validation of %q should succeed", "Conditions with valid timestamps")
}
// Conditions where notBefore is 45 seconds after now
notBefore = p.now().Add(+time.Duration(45) * time.Second)
cond.NotBefore = xmlTime(notBefore)
err = p.validateConditions(assert)
if err == nil {
t.Fatalf("validation of %q should fail", "Conditions where notBefore is 45 seconds after now")
}
// Conditions where notBefore is 15 seconds after now
notBefore = p.now().Add(+time.Duration(15) * time.Second)
cond.NotBefore = xmlTime(notBefore)
err = p.validateConditions(assert)
if err != nil {
t.Fatalf("validation of %q should succeed", "Conditions where notBefore is 15 seconds after now")
}
// Audiences contains the redirectURI
validAudience := audience{Value: p.redirectURI}
cond.AudienceRestriction.Audiences = []audience{validAudience}
err = p.validateConditions(assert)
if err != nil {
t.Fatalf("validation of %q should succeed: %v", "Audiences contains the redirectURI", err)
}
// Audiences is not empty and not contains the issuer
invalidAudience := audience{Value: "invalid"}
cond.AudienceRestriction.Audiences = []audience{invalidAudience}
err = p.validateConditions(assert)
if err == nil {
t.Fatalf("validation of %q should succeed", "Audiences is not empty and not contains the issuer")
}
}

3
connector/saml/types.go
View File

@ -86,6 +86,7 @@ type nameID struct {
type subjectConfirmationData struct {
XMLName xml.Name `xml:"urn:oasis:names:tc:SAML:2.0:assertion SubjectConfirmationData"`
NotBefore xmlTime `xml:"NotBefore,attr,omitempty"`
NotOnOrAfter xmlTime `xml:"NotOnOrAfter,attr,omitempty"`
Recipient string `xml:"Recipient,attr,omitempty"`
InResponseTo string `xml:"InResponseTo,attr,omitempty"`
@ -115,7 +116,7 @@ type conditions struct {
NotBefore xmlTime `xml:"NotBefore,attr,omitempty"`
NotOnOrAfter xmlTime `xml:"NotOnOrAfter,attr,omitempty"`
AudienceRestriction *audienceRestriction `xml:"AudienceRestriction,omitempty"`
AudienceRestriction []audienceRestriction `xml:"AudienceRestriction,omitempty"`
}
type statusCode struct {