diff --git a/CHANGES/7835.bugfix b/CHANGES/7835.bugfix
new file mode 100644
index 00000000000..4ce3af4f6f6
--- /dev/null
+++ b/CHANGES/7835.bugfix
@@ -0,0 +1 @@
+Fixed arbitrary sequence types being allowed to inject headers via version parameter -- by :user:`Dreamsorcerer`
diff --git a/aiohttp/client_reqrep.py b/aiohttp/client_reqrep.py
index 851ab220b8a..4cea7466d8d 100644
--- a/aiohttp/client_reqrep.py
+++ b/aiohttp/client_reqrep.py
@@ -706,8 +706,8 @@ async def send(self, conn: "Connection") -> "ClientResponse":
             self.headers[hdrs.CONNECTION] = connection
 
         # status + headers
-        status_line = "{0} {1} HTTP/{2[0]}.{2[1]}".format(
-            self.method, path, self.version
+        status_line = "{0} {1} HTTP/{v.major}.{v.minor}".format(
+            self.method, path, v=self.version
         )
         await writer.write_headers(status_line, self.headers)
 
diff --git a/tests/test_client_request.py b/tests/test_client_request.py
index 0f58d752de2..c8ce98d4034 100644
--- a/tests/test_client_request.py
+++ b/tests/test_client_request.py
@@ -21,6 +21,7 @@
     _gen_default_accept_encoding,
     _merge_ssl_params,
 )
+from aiohttp.http import HttpVersion
 from aiohttp.test_utils import make_mocked_coro
 
 
@@ -623,18 +624,18 @@ async def test_connection_header(loop, conn) -> None:
     req.headers.clear()
 
     req.keep_alive.return_value = True
-    req.version = (1, 1)
+    req.version = HttpVersion(1, 1)
     req.headers.clear()
     await req.send(conn)
     assert req.headers.get("CONNECTION") is None
 
-    req.version = (1, 0)
+    req.version = HttpVersion(1, 0)
     req.headers.clear()
     await req.send(conn)
     assert req.headers.get("CONNECTION") == "keep-alive"
 
     req.keep_alive.return_value = False
-    req.version = (1, 1)
+    req.version = HttpVersion(1, 1)
     req.headers.clear()
     await req.send(conn)
     assert req.headers.get("CONNECTION") == "close"
@@ -1161,6 +1162,19 @@ async def gen():
     resp.close()
 
 
+async def test_bad_version(loop, conn) -> None:
+    req = ClientRequest(
+        "GET",
+        URL("http://python.org"),
+        loop=loop,
+        headers={"Connection": "Close"},
+        version=("1", "1\r\nInjected-Header: not allowed"),
+    )
+
+    with pytest.raises(AttributeError):
+        await req.send(conn)
+
+
 async def test_custom_response_class(loop, conn) -> None:
     class CustomResponse(ClientResponse):
         def read(self, decode=False):