diff --git a/implementation/configuration/src/configuration_impl.cpp b/implementation/configuration/src/configuration_impl.cpp
index 34fd34320..49d4cfcff 100644
--- a/implementation/configuration/src/configuration_impl.cpp
+++ b/implementation/configuration/src/configuration_impl.cpp
@@ -3453,7 +3453,7 @@ std::uint32_t configuration_impl::get_max_message_size_reliable(const std::strin
             return its_port->second;
         }
     }
-    return (max_reliable_message_size_ == 0) ? ((VSOMEIP_MAX_TCP_MESSAGE_SIZE == 0) ? MESSAGE_SIZE_UNLIMITED : VSOMEIP_MAX_TCP_MESSAGE_SIZE)
+    return (max_reliable_message_size_ == 0) ? ((VSOMEIP_MAX_TCP_MESSAGE_SIZE == 0) ? VSOMEIP_MAX_TCP_MESSAGE_SIZE_DEFAULT : VSOMEIP_MAX_TCP_MESSAGE_SIZE)
                                              : max_reliable_message_size_;
 }
 
diff --git a/implementation/endpoints/src/tcp_server_endpoint_impl.cpp b/implementation/endpoints/src/tcp_server_endpoint_impl.cpp
index b79f65df2..9e9199de0 100644
--- a/implementation/endpoints/src/tcp_server_endpoint_impl.cpp
+++ b/implementation/endpoints/src/tcp_server_endpoint_impl.cpp
@@ -677,7 +677,7 @@ void tcp_server_endpoint_impl::connection::receive_cbk(boost::system::error_code
                         its_lock.unlock();
                         wait_until_sent(boost::asio::error::operation_aborted);
                         return;
-                    } else if (max_message_size_ != MESSAGE_SIZE_UNLIMITED && current_message_size > max_message_size_) {
+                    } else if (current_message_size > max_message_size_) {
                         recv_buffer_size_ = 0;
                         recv_buffer_.resize(recv_buffer_size_initial_, 0x0);
                         recv_buffer_.shrink_to_fit();
diff --git a/interface/vsomeip/defines.hpp b/interface/vsomeip/defines.hpp
index 8307acbb9..3b688f99e 100644
--- a/interface/vsomeip/defines.hpp
+++ b/interface/vsomeip/defines.hpp
@@ -14,6 +14,12 @@ constexpr std::uint8_t VSOMEIP_PROTOCOL_VERSION = 0x1;
 constexpr std::size_t VSOMEIP_MAX_LOCAL_MESSAGE_SIZE = 0;
 // 0 = unlimited, if not specified otherwise via configuration file
 constexpr std::size_t VSOMEIP_MAX_TCP_MESSAGE_SIZE = 0;
+// Safe default cap for TCP receive buffer when neither VSOMEIP_MAX_TCP_MESSAGE_SIZE
+// nor the runtime "max-message-size-reliable" JSON option is set.  Prevents unbounded
+// heap growth from an attacker-supplied SOME/IP Length field (CWE-789, issue #1009).
+// Operators who genuinely need larger messages should set max-message-size-reliable
+// in their vsomeip configuration file.
+constexpr std::uint32_t VSOMEIP_MAX_TCP_MESSAGE_SIZE_DEFAULT = 1048576U; // 1 MiB
 constexpr std::size_t VSOMEIP_MAX_UDP_MESSAGE_SIZE = 1416;
 
 constexpr std::size_t VSOMEIP_PACKET_SIZE = VSOMEIP_MAX_UDP_MESSAGE_SIZE;