diff --git a/libwvdrmengine/cdm/core/include/properties.h b/libwvdrmengine/cdm/core/include/properties.h
index 72b8e376..360cac5c 100644
--- a/libwvdrmengine/cdm/core/include/properties.h
+++ b/libwvdrmengine/cdm/core/include/properties.h
@@ -142,6 +142,7 @@ class Properties {
   static void InitOnce();
 
   static std::mutex init_mutex_;
+  static std::mutex session_mutex_;
   static bool is_initialized_;
   static bool oem_crypto_use_secure_buffers_;
   static bool oem_crypto_use_fifo_;
diff --git a/libwvdrmengine/cdm/core/src/properties.cpp b/libwvdrmengine/cdm/core/src/properties.cpp
index 1eeb8e17..746a437b 100644
--- a/libwvdrmengine/cdm/core/src/properties.cpp
+++ b/libwvdrmengine/cdm/core/src/properties.cpp
@@ -12,7 +12,10 @@ const char* kSecurityLevelDirs[] = {"L1/", "L3/"};
 }  // namespace
 
 namespace wvcdm {
+using UniqueLock = std::unique_lock<std::mutex>;
+
 std::mutex Properties::init_mutex_;
+std::mutex Properties::session_mutex_;
 bool Properties::is_initialized_ = false;
 bool Properties::oem_crypto_use_secure_buffers_;
 bool Properties::oem_crypto_use_fifo_;
@@ -26,6 +29,7 @@ std::unique_ptr<CdmClientPropertySetMap> Properties::session_property_set_;
 
 bool Properties::AddSessionPropertySet(const CdmSessionId& session_id,
                                        CdmClientPropertySet* property_set) {
+  UniqueLock lock(session_mutex_);
   if (!session_property_set_) {
     return false;
   }
@@ -37,6 +41,7 @@ bool Properties::AddSessionPropertySet(const CdmSessionId& session_id,
 }
 
 bool Properties::RemoveSessionPropertySet(const CdmSessionId& session_id) {
+  UniqueLock lock(session_mutex_);
   if (!session_property_set_) {
     return false;
   }
@@ -45,6 +50,7 @@ bool Properties::RemoveSessionPropertySet(const CdmSessionId& session_id) {
 
 CdmClientPropertySet* Properties::GetCdmClientPropertySet(
     const CdmSessionId& session_id) {
+  // Call must obtain |session_mutex_|.
   if (session_property_set_) {
     CdmClientPropertySetMap::iterator it =
         session_property_set_->find(session_id);
@@ -57,6 +63,7 @@ CdmClientPropertySet* Properties::GetCdmClientPropertySet(
 
 bool Properties::GetApplicationId(const CdmSessionId& session_id,
                                   std::string* app_id) {
+  UniqueLock lock(session_mutex_);
   const CdmClientPropertySet* property_set =
       GetCdmClientPropertySet(session_id);
   if (property_set == nullptr) {
@@ -68,6 +75,7 @@ bool Properties::GetApplicationId(const CdmSessionId& session_id,
 
 bool Properties::GetServiceCertificate(const CdmSessionId& session_id,
                                        std::string* service_certificate) {
+  UniqueLock lock(session_mutex_);
   const CdmClientPropertySet* property_set =
       GetCdmClientPropertySet(session_id);
   if (property_set == nullptr) {
@@ -79,6 +87,7 @@ bool Properties::GetServiceCertificate(const CdmSessionId& session_id,
 
 bool Properties::SetServiceCertificate(const CdmSessionId& session_id,
                                        const std::string& service_certificate) {
+  UniqueLock lock(session_mutex_);
   CdmClientPropertySet* property_set = GetCdmClientPropertySet(session_id);
   if (property_set == nullptr) {
     return false;
@@ -88,6 +97,7 @@ bool Properties::SetServiceCertificate(const CdmSessionId& session_id,
 }
 
 bool Properties::UsePrivacyMode(const CdmSessionId& session_id) {
+  UniqueLock lock(session_mutex_);
   const CdmClientPropertySet* property_set =
       GetCdmClientPropertySet(session_id);
   if (property_set == nullptr) {
@@ -97,6 +107,7 @@ bool Properties::UsePrivacyMode(const CdmSessionId& session_id) {
 }
 
 uint32_t Properties::GetSessionSharingId(const CdmSessionId& session_id) {
+  UniqueLock lock(session_mutex_);
   const CdmClientPropertySet* property_set =
       GetCdmClientPropertySet(session_id);
   if (property_set == nullptr) {
diff --git a/libwvdrmengine/cdm/src/properties_android.cpp b/libwvdrmengine/cdm/src/properties_android.cpp
index f3383566..eb807aca 100644
--- a/libwvdrmengine/cdm/src/properties_android.cpp
+++ b/libwvdrmengine/cdm/src/properties_android.cpp
@@ -52,7 +52,10 @@ void Properties::InitOnce() {
   allow_restore_of_offline_licenses_with_release_ =
       kAllowRestoreOfflineLicenseWithRelease;
   delay_oem_crypto_termination_ = kPropertyDelayOemCryptoTermination;
-  session_property_set_.reset(new CdmClientPropertySetMap());
+  {
+    std::unique_lock<std::mutex> lock(session_mutex_);
+    session_property_set_.reset(new CdmClientPropertySetMap());
+  }
 }
 
 bool Properties::GetCompanyName(std::string* company_name) {