diff --git a/airflow-core/newsfragments/70264.bugfix.rst b/airflow-core/newsfragments/70264.bugfix.rst
new file mode 100644
index 0000000000000..9647401b0e896
--- /dev/null
+++ b/airflow-core/newsfragments/70264.bugfix.rst
@@ -0,0 +1 @@
+The ``port`` field on the Connection API (``POST``/``PATCH /connections``) now validates that the value is a valid TCP/UDP port number (between 1 and 65535). Previously, negative numbers, ``0``, and values above 65535 were silently accepted.
\ No newline at end of file
diff --git a/airflow-core/src/airflow/api_fastapi/core_api/datamodels/connections.py b/airflow-core/src/airflow/api_fastapi/core_api/datamodels/connections.py
index 34cfe47334893..ec3d01889b78f 100644
--- a/airflow-core/src/airflow/api_fastapi/core_api/datamodels/connections.py
+++ b/airflow-core/src/airflow/api_fastapi/core_api/datamodels/connections.py
@@ -191,7 +191,12 @@ class ConnectionBody(StrictBaseModel):
     host: str | None = Field(default=None)
     login: str | None = Field(default=None)
     schema_: str | None = Field(None, alias="schema")
-    port: int | None = Field(default=None)
+    port: int | None = Field(
+        default=None,
+        ge=1,
+        le=65535,
+        description="TCP/UDP port number. Must be between 1 and 65535.",
+    )
     password: str | None = Field(default=None)
     extra: str | None = Field(default=None)
     team_name: str | None = Field(max_length=50, default=None)
diff --git a/airflow-core/src/airflow/api_fastapi/core_api/openapi/v2-rest-api-generated.yaml b/airflow-core/src/airflow/api_fastapi/core_api/openapi/v2-rest-api-generated.yaml
index 3ddcf0b1c8d82..53d4b9fef0a06 100644
--- a/airflow-core/src/airflow/api_fastapi/core_api/openapi/v2-rest-api-generated.yaml
+++ b/airflow-core/src/airflow/api_fastapi/core_api/openapi/v2-rest-api-generated.yaml
@@ -13251,8 +13251,11 @@ components:
         port:
           anyOf:
           - type: integer
+            maximum: 65535.0
+            minimum: 1.0
           - type: 'null'
           title: Port
+          description: TCP/UDP port number. Must be between 1 and 65535.
         password:
           anyOf:
           - type: string
@@ -13323,8 +13326,11 @@ components:
         port:
           anyOf:
           - type: integer
+            maximum: 65535.0
+            minimum: 1.0
           - type: 'null'
           title: Port
+          description: TCP/UDP port number. Must be between 1 and 65535.
         password:
           anyOf:
           - type: string
@@ -13406,8 +13412,11 @@ components:
         port:
           anyOf:
           - type: integer
+            maximum: 65535.0
+            minimum: 1.0
           - type: 'null'
           title: Port
+          description: TCP/UDP port number. Must be between 1 and 65535.
         password:
           anyOf:
           - type: string
diff --git a/airflow-core/tests/unit/api_fastapi/core_api/routes/public/test_connections.py b/airflow-core/tests/unit/api_fastapi/core_api/routes/public/test_connections.py
index 231a7ca7b22ef..5ec9e7c687a27 100644
--- a/airflow-core/tests/unit/api_fastapi/core_api/routes/public/test_connections.py
+++ b/airflow-core/tests/unit/api_fastapi/core_api/routes/public/test_connections.py
@@ -368,6 +368,28 @@ def test_post_should_respond_422_for_invalid_conn_id(self, test_client, body):
             ]
         }
 
+    @pytest.mark.parametrize(
+        "port",
+        [-1, 0, 65536, 99999, 123456789],
+    )
+    def test_post_should_respond_422_for_invalid_port(self, test_client, port):
+        body = {"connection_id": TEST_CONN_ID, "conn_type": TEST_CONN_TYPE, "port": port}
+        response = test_client.post("/connections", json=body)
+        assert response.status_code == 422
+        detail = response.json()["detail"][0]
+        assert detail["loc"] == ["body", "port"]
+        assert detail["input"] == port
+
+    @pytest.mark.parametrize(
+        "port",
+        [1, 22, 8080, 65535],
+    )
+    def test_post_should_respond_201_for_valid_port(self, test_client, session, port):
+        body = {"connection_id": TEST_CONN_ID, "conn_type": TEST_CONN_TYPE, "port": port}
+        response = test_client.post("/connections", json=body)
+        assert response.status_code == 201
+        assert response.json()["port"] == port
+
     @conf_vars({("core", "multi_team"): "False"})
     def test_post_rejects_team_name_when_multi_team_disabled(self, test_client):
         response = test_client.post(
@@ -1013,6 +1035,19 @@ def test_patch_with_update_mask_rejects_extra_fields(self, test_client):
         )
         assert response.status_code == 422
 
+    @pytest.mark.parametrize(
+        "port",
+        [-1, 0, 65536, 99999],
+    )
+    def test_patch_should_respond_422_for_invalid_port(self, test_client, port):
+        self.create_connection()
+        response = test_client.patch(
+            f"/connections/{TEST_CONN_ID}",
+            json={"connection_id": TEST_CONN_ID, "conn_type": TEST_CONN_TYPE, "port": port},
+            params={"update_mask": ["port"]},
+        )
+        assert response.status_code == 422
+
     @conf_vars({("core", "multi_team"): "False"})
     def test_patch_rejects_team_name_when_multi_team_disabled(self, test_client):
         self.create_connection()