aiohttp ClientConnectionError SSL shutdown timed out when closing Microsoft Graph connection

Question

I’m using Python 3.11.11 and aiohttp 3.11.18 to talk to Microsoft Graph (endpoints like /sendMail and /delta). Every request completes successfully (I get 200 or 202), but as soon as aiohttp tries to tear down the HTTPS connection I see:

ClientConnectionError: Connection lost: SSL shutdown timed out

This only started happening around May 30, 2025 and I never see the error when calling Google APIs or other services. It only appears when the aiohttp.ClientSession (or its TCPConnector) is closed or cleaned up after a Graph call.

What’s going on here? Has Microsoft Graph changed its TLS shutdown behavior recently? How can I either work around or properly handle this “close_notify” handshake timeout?

Environment

• Python 3.11.11 (Windows/Linux)
• aiohttp 3.11.18
• msal 1.32.3
• Observed only with Microsoft Graph endpoints

Any pointers or confirmation of a Graph-side TLS change would be greatly appreciated!

Answer 1

Hi everyone,

This issue with aiohttp throwing SSL shutdown timeouts has been identified and tracked here: https://github.com/aio-libs/aiohttp/issues/11091

It's not limited to one use case—it has also impacted interactions with Microsoft services, such as Azure SDK for Python: https://github.com/Azure/azure-sdk-for-python/issues/41363

Recommended temporary workaround: Pin your aiohttp version to 3.12.3, which avoids the regression for now.

You can do this in your requirements.txt or pyproject.toml until a more permanent fix is released.

Hope this helps!

Answer 2

I am having the same issue. Were you able you fix this error?