diff --git a/handlers/cloudspan_polling_requirements.txt b/handlers/cloudspan_polling_requirements.txt
index 3d4986a..839583f 100644
--- a/handlers/cloudspan_polling_requirements.txt
+++ b/handlers/cloudspan_polling_requirements.txt
@@ -53,7 +53,7 @@ proto-google-cloud-pubsub-v1==0.15.4
 proto-google-cloud-spanner-admin-database-v1==0.15.3
 proto-google-cloud-spanner-admin-instance-v1==0.15.3
 proto-google-cloud-spanner-v1==0.15.3
-protobuf==3.4.0
+protobuf==3.18.3
 pyasn1==0.3.7
 pyasn1-modules==0.1.5
 python-dateutil==2.6.1
diff --git a/handlers/cloudspan_requirements.txt b/handlers/cloudspan_requirements.txt
index 755d59e..3a8451b 100644
--- a/handlers/cloudspan_requirements.txt
+++ b/handlers/cloudspan_requirements.txt
@@ -53,7 +53,7 @@ proto-google-cloud-pubsub-v1==0.15.4
 proto-google-cloud-spanner-admin-database-v1==0.15.3
 proto-google-cloud-spanner-admin-instance-v1==0.15.3
 proto-google-cloud-spanner-v1==0.15.3
-protobuf==3.4.0
+protobuf==3.18.3
 pyasn1==0.3.7
 pyasn1-modules==0.1.5
 python-dateutil==2.6.1
diff --git a/handlers/handoff_poller_requirements.txt b/handlers/handoff_poller_requirements.txt
index 94b2d77..ad5d455 100644
--- a/handlers/handoff_poller_requirements.txt
+++ b/handlers/handoff_poller_requirements.txt
@@ -53,7 +53,7 @@ proto-google-cloud-pubsub-v1==0.15.4
 proto-google-cloud-spanner-admin-database-v1==0.15.3
 proto-google-cloud-spanner-admin-instance-v1==0.15.3
 proto-google-cloud-spanner-v1==0.15.3
-protobuf==3.4.0
+protobuf==3.18.3
 pyasn1==0.3.7
 pyasn1-modules==0.1.5
 python-dateutil==2.6.1
diff --git a/handlers/handoff_requirements.txt b/handlers/handoff_requirements.txt
index b08c402..71797a2 100644
--- a/handlers/handoff_requirements.txt
+++ b/handlers/handoff_requirements.txt
@@ -53,7 +53,7 @@ proto-google-cloud-pubsub-v1==0.15.4
 proto-google-cloud-spanner-admin-database-v1==0.15.3
 proto-google-cloud-spanner-admin-instance-v1==0.15.3
 proto-google-cloud-spanner-v1==0.15.3
-protobuf==3.4.0
+protobuf==3.18.3
 pyasn1==0.3.7
 pyasn1-modules==0.1.5
 python-dateutil==2.6.1
diff --git a/requirements.txt b/requirements.txt
index 960804e..857c431 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -60,7 +60,7 @@ proto-google-cloud-pubsub-v1==0.15.4
 proto-google-cloud-spanner-admin-database-v1==0.15.3
 proto-google-cloud-spanner-admin-instance-v1==0.15.3
 proto-google-cloud-spanner-v1==0.15.3
-protobuf==3.4.0
+protobuf==3.18.3
 pyasn1==0.3.7
 pyasn1-modules==0.1.5
 python-dateutil==2.6.1