diff --git a/go.mod b/go.mod
index d471e3ebe..077882d17 100644
--- a/go.mod
+++ b/go.mod
@@ -111,7 +111,7 @@ require (
 	go.uber.org/atomic v1.3.2 // indirect
 	go.uber.org/multierr v1.1.0 // indirect
 	go.uber.org/zap v1.9.1 // indirect
-	golang.org/x/crypto v0.0.0-20190222235706-ffb98f73852f
+	golang.org/x/crypto v0.0.0-20190228050851-31a38585487a
 	golang.org/x/net v0.0.0-20190213061140-3a22650c66bd
 	golang.org/x/oauth2 v0.0.0-20190220154721-9b3c75971fc9
 	google.golang.org/api v0.1.0
diff --git a/go.sum b/go.sum
index a124638f7..eb7495465 100644
--- a/go.sum
+++ b/go.sum
@@ -419,6 +419,8 @@ golang.org/x/crypto v0.0.0-20190219172222-a4c6cb3142f2 h1:NwxKRvbkH5MsNkvOtPZi3/
 golang.org/x/crypto v0.0.0-20190219172222-a4c6cb3142f2/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
 golang.org/x/crypto v0.0.0-20190222235706-ffb98f73852f h1:qWFY9ZxP3tfI37wYIs/MnIAqK0vlXp1xnYEa5HxFSSY=
 golang.org/x/crypto v0.0.0-20190222235706-ffb98f73852f/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
+golang.org/x/crypto v0.0.0-20190228050851-31a38585487a h1:53VJPSIh1mc/PLK5AlXoj1HHfovtbS77YvYJ0AqjSgE=
+golang.org/x/crypto v0.0.0-20190228050851-31a38585487a/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/exp v0.0.0-20190121172915-509febef88a4/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
 golang.org/x/lint v0.0.0-20180702182130-06c8688daad7/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
 golang.org/x/lint v0.0.0-20181026193005-c67002cb31c3/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
@@ -453,6 +455,7 @@ golang.org/x/sys v0.0.0-20181029174526-d69651ed3497/go.mod h1:STP8DvDyc/dI5b8T5h
 golang.org/x/sys v0.0.0-20181213200352-4d1cda033e06/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190129075346-302c3dd5f1cc h1:WiYx1rIFmx8c0mXAFtv5D/mHyKe1+jmuP7PViuwqwuQ=
 golang.org/x/sys v0.0.0-20190129075346-302c3dd5f1cc/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190221075227-b4e8571b14e0 h1:bzeyCHgoAyjZjAhvTpks+qM7sdlh4cCSitmXeCEO3B4=
 golang.org/x/sys v0.0.0-20190221075227-b4e8571b14e0/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190222072716-a9d3bda3a223 h1:DH4skfRX4EBpamg7iV4ZlCpblAHI6s6TDM39bFZumv8=
diff --git a/vendor/golang.org/x/crypto/ssh/agent/server.go b/vendor/golang.org/x/crypto/ssh/agent/server.go
index a19497627..6e7a1e02f 100644
--- a/vendor/golang.org/x/crypto/ssh/agent/server.go
+++ b/vendor/golang.org/x/crypto/ssh/agent/server.go
@@ -541,6 +541,9 @@ func ServeAgent(agent Agent, c io.ReadWriter) error {
 			return err
 		}
 		l := binary.BigEndian.Uint32(length[:])
+		if l == 0 {
+			return fmt.Errorf("agent: request size is 0")
+		}
 		if l > maxAgentResponseBytes {
 			// We also cap requests.
 			return fmt.Errorf("agent: request too large: %d", l)
diff --git a/vendor/modules.txt b/vendor/modules.txt
index 0d8283814..a95a7b337 100644
--- a/vendor/modules.txt
+++ b/vendor/modules.txt
@@ -458,7 +458,7 @@ go.opencensus.io/trace/propagation
 go.opencensus.io
 go.opencensus.io/stats/internal
 go.opencensus.io/internal/tagencoding
-# golang.org/x/crypto v0.0.0-20190222235706-ffb98f73852f
+# golang.org/x/crypto v0.0.0-20190228050851-31a38585487a
 golang.org/x/crypto/ssh
 golang.org/x/crypto/ssh/agent
 golang.org/x/crypto/ssh/knownhosts