Configurable deflate-bomb protection

decode_logout_request.go

@@ -49,7 +49,7 @@ func (sp *SAMLServiceProvider) ValidateEncodedLogoutRequestPOST(encodedRequest s
 	}
 
 	// Parse the raw request - parseResponse is generic
-	doc, el, err := parseResponse(raw)
+	doc, el, err := parseResponse(raw, sp.MaximumDecompressedBodySize)
 	if err != nil {
 		return nil, err
 	}

decode_response.go

@@ -21,15 +21,19 @@ import (
 	"crypto/x509"
 	"encoding/base64"
 	"fmt"
-	"io/ioutil"
+	"io"
 
 	"encoding/xml"
 
 	"github.com/beevik/etree"
+	rtvalidator "github.com/mattermost/xml-roundtrip-validator"
 	"github.com/russellhaering/gosaml2/types"
 	dsig "github.com/russellhaering/goxmldsig"
 	"github.com/russellhaering/goxmldsig/etreeutils"
-	rtvalidator "github.com/mattermost/xml-roundtrip-validator"
+)
+
+const (
+	defaultMaxDecompressedResponseSize = 5 * 1024 * 1024
 )
 
 func (sp *SAMLServiceProvider) validationContext() *dsig.ValidationContext {
@@ -174,7 +178,7 @@ func (sp *SAMLServiceProvider) decryptAssertions(el *etree.Element) error {
 			return fmt.Errorf("unable to decrypt encrypted assertion: %v", derr)
 		}
 
-		doc, _, err := parseResponse(raw)
+		doc, _, err := parseResponse(raw, sp.MaximumDecompressedBodySize)
 		if err != nil {
 			return fmt.Errorf("unable to create element from decrypted assertion bytes: %v", err)
 		}
@@ -250,17 +254,17 @@ func (sp *SAMLServiceProvider) validateAssertionSignatures(el *etree.Element) er
 	}
 }
 
-//ValidateEncodedResponse both decodes and validates, based on SP
-//configuration, an encoded, signed response. It will also appropriately
-//decrypt a response if the assertion was encrypted
+// ValidateEncodedResponse both decodes and validates, based on SP
+// configuration, an encoded, signed response. It will also appropriately
+// decrypt a response if the assertion was encrypted
 func (sp *SAMLServiceProvider) ValidateEncodedResponse(encodedResponse string) (*types.Response, error) {
 	raw, err := base64.StdEncoding.DecodeString(encodedResponse)
 	if err != nil {
 		return nil, err
 	}
 
 	// Parse the raw response
-	doc, el, err := parseResponse(raw)
+	doc, el, err := parseResponse(raw, sp.MaximumDecompressedBodySize)
 	if err != nil {
 		return nil, err
 	}
@@ -330,7 +334,7 @@ func DecodeUnverifiedBaseResponse(encodedResponse string) (*types.UnverifiedBase
 
 	var response *types.UnverifiedBaseResponse
 
-	err = maybeDeflate(raw, func(maybeXML []byte) error {
+	err = maybeDeflate(raw, defaultMaxDecompressedResponseSize, func(maybeXML []byte) error {
 		response = &types.UnverifiedBaseResponse{}
 		return xml.Unmarshal(maybeXML, response)
 	})
@@ -344,26 +348,37 @@ func DecodeUnverifiedBaseResponse(encodedResponse string) (*types.UnverifiedBase
 // maybeDeflate invokes the passed decoder over the passed data. If an error is
 // returned, it then attempts to deflate the passed data before re-invoking
 // the decoder over the deflated data.
-func maybeDeflate(data []byte, decoder func([]byte) error) error {
+func maybeDeflate(data []byte, maxSize int64, decoder func([]byte) error) error {
 	err := decoder(data)
 	if err == nil {
 		return nil
 	}
 
-	deflated, err := ioutil.ReadAll(flate.NewReader(bytes.NewReader(data)))
+	// Default to 5MB max size
+	if maxSize == 0 {
+		maxSize = defaultMaxDecompressedResponseSize
+	}
+
+	lr := io.LimitReader(flate.NewReader(bytes.NewReader(data)), maxSize+1)
+
+	deflated, err := io.ReadAll(lr)
 	if err != nil {
 		return err
 	}
 
+	if int64(len(deflated)) > maxSize {
+		return fmt.Errorf("deflated response exceeds maximum size of %d bytes", maxSize)
+	}
+
 	return decoder(deflated)
 }
 
 // parseResponse is a helper function that was refactored out so that the XML parsing behavior can be isolated and unit tested
-func parseResponse(xml []byte) (*etree.Document, *etree.Element, error) {
+func parseResponse(xml []byte, maxSize int64) (*etree.Document, *etree.Element, error) {
 	var doc *etree.Document
 	var rawXML []byte
 
-	err := maybeDeflate(xml, func(xml []byte) error {
+	err := maybeDeflate(xml, maxSize, func(xml []byte) error {
 		doc = etree.NewDocument()
 		rawXML = xml
 		return doc.ReadFromBytes(xml)
@@ -395,7 +410,7 @@ func DecodeUnverifiedLogoutResponse(encodedResponse string) (*types.LogoutRespon
 
 	var response *types.LogoutResponse
 
-	err = maybeDeflate(raw, func(maybeXML []byte) error {
+	err = maybeDeflate(raw, defaultMaxDecompressedResponseSize, func(maybeXML []byte) error {
 		response = &types.LogoutResponse{}
 		return xml.Unmarshal(maybeXML, response)
 	})
@@ -413,7 +428,7 @@ func (sp *SAMLServiceProvider) ValidateEncodedLogoutResponsePOST(encodedResponse
 	}
 
 	// Parse the raw response
-	doc, el, err := parseResponse(raw)
+	doc, el, err := parseResponse(raw, sp.MaximumDecompressedBodySize)
 	if err != nil {
 		return nil, err
 	}

decode_response_test.go

@@ -25,9 +25,9 @@ import (
 	"time"
 
 	"github.com/jonboulle/clockwork"
-	"github.com/russellhaering/goxmldsig"
-	"github.com/stretchr/testify/require"
 	rtvalidator "github.com/mattermost/xml-roundtrip-validator"
+	dsig "github.com/russellhaering/goxmldsig"
+	"github.com/stretchr/testify/require"
 )
 
 const (
@@ -169,7 +169,7 @@ func TestDecodeColonsInLocalNames(t *testing.T) {
 		t.Skip()
 	}
 
-	_, _, err := parseResponse([]byte(`<x::Root/>`))
+	_, _, err := parseResponse([]byte(`<x::Root/>`), 0)
 	require.Error(t, err)
 }
 
@@ -180,7 +180,7 @@ func TestDecodeDoubleColonInjectionAttackResponse(t *testing.T) {
 		t.Skip()
 	}
 
-	_, _, err := parseResponse([]byte(doubleColonAssertionInjectionAttackResponse))
+	_, _, err := parseResponse([]byte(doubleColonAssertionInjectionAttackResponse), 0)
 	require.Error(t, err)
 }
 
@@ -194,7 +194,7 @@ func TestMalFormedInput(t *testing.T) {
 	}
 
 	sp := &SAMLServiceProvider{
-		Clock: dsig.NewFakeClock(clockwork.NewFakeClockAt(time.Date(2019, 8, 12, 12, 00, 52, 718, time.UTC))),
+		Clock:                       dsig.NewFakeClock(clockwork.NewFakeClockAt(time.Date(2019, 8, 12, 12, 00, 52, 718, time.UTC))),
 		AssertionConsumerServiceURL: "https://saml2.test.astuart.co/sso/saml2",
 		SignAuthnRequests:           true,
 		IDPCertificateStore:         &certStore,
@@ -203,4 +203,27 @@ func TestMalFormedInput(t *testing.T) {
 	base64Input := base64.StdEncoding.EncodeToString([]byte(badInput))
 	_, err = sp.RetrieveAssertionInfo(base64Input)
 	require.Errorf(t, err, "parent is nil")
-}
+}
+
+func TestCompressionBombInput(t *testing.T) {
+	bs, err := ioutil.ReadFile("./testdata/saml_compressed.post")
+	require.NoError(t, err, "couldn't read compressed post")
+
+	block, _ := pem.Decode([]byte(oktaCert))
+
+	idpCert, err := x509.ParseCertificate(block.Bytes)
+	require.NoError(t, err, "couldn't parse okta cert pem block")
+
+	sp := SAMLServiceProvider{
+		AssertionConsumerServiceURL: "https://f1f51ddc.ngrok.io/api/sso/saml2/acs/58cafd0573d4f375b8e70e8e",
+		SPKeyStore:                  dsig.TLSCertKeyStore(cert),
+		IDPCertificateStore: &dsig.MemoryX509CertificateStore{
+			Roots: []*x509.Certificate{idpCert},
+		},
+		Clock:                       dsig.NewFakeClock(clockwork.NewFakeClockAt(time.Date(2017, 3, 17, 20, 00, 0, 0, time.UTC))),
+		MaximumDecompressedBodySize: 2048,
+	}
+
+	_, err = sp.RetrieveAssertionInfo(string(bs))
+	require.NoError(t, err, "Assertion info should be retrieved with no error")
+}

saml.go

@@ -74,8 +74,14 @@ type SAMLServiceProvider struct {
 	SkipSignatureValidation bool
 	AllowMissingAttributes  bool
 	Clock                   *dsig.Clock
-	signingContextMu        sync.RWMutex
-	signingContext          *dsig.SigningContext
+
+	// MaximumDecompressedBodySize is the maximum size to which a compressed
+	// SAML document will be decompressed. If a compresed document is exceeds
+	// this size during decompression an error will be returned.
+	MaximumDecompressedBodySize int64
+
+	signingContextMu sync.RWMutex
+	signingContext   *dsig.SigningContext
 }
 
 // RequestedAuthnContext controls which authentication mechanisms are requested of

saml_test.go

@@ -353,7 +353,7 @@ func TestSAMLCommentInjection(t *testing.T) {
 	*/
 
 	// To show that we are not vulnerable, we want to prove that we get the canonicalized value using our parser
-	_, el, err := parseResponse([]byte(commentInjectionAttackResponse))
+	_, el, err := parseResponse([]byte(commentInjectionAttackResponse), 0)
 	require.NoError(t, err)
 	decodedResponse := &types.Response{}
 	err = xmlUnmarshalElement(el, decodedResponse)