I'm running in local mode on my Mac, so there is a lot of traffic going across the wire.
[10:52:53.939][10.0.115.19:0] client disconnect
[10:52:53.940][10.0.115.19:0] Server QUIC handshake failed. connection closed
[10:52:53.941][10.0.115.19:0] server disconnect 17.248.168.106:443
[10:52:53.941][10.0.115.19:0] Unable to establish QUIC connection with server (connection closed). Trying to establish QUIC with client anyway. If you plan to redirect requests away from this server, consider setting `connection_strategy` to `lazy` to suppress early connections.
[10:52:53.943][10.0.115.19:0] Client QUIC handshake failed. connection closed early
[10:52:53.944][10.0.115.19:0] mitmproxy has crashed!
Traceback (most recent call last):
File "mitmproxy/proxy/server.py", line 390, in server_event
File "mitmproxy/proxy/layer.py", line 181, in handle_event
File "mitmproxy/proxy/layer.py", line 270, in handle_event
File "mitmproxy/proxy/layer.py", line 181, in handle_event
File "mitmproxy/proxy/layers/quic/_stream_layers.py", line 91, in _handle_event
File "mitmproxy/proxy/tunnel.py", line 98, in _handle_event
File "mitmproxy/proxy/layers/quic/_stream_layers.py", line 397, in event_to_child
File "mitmproxy/proxy/layers/quic/_stream_layers.py", line 96, in event_to_child
File "mitmproxy/proxy/tunnel.py", line 153, in event_to_child
File "mitmproxy/proxy/layer.py", line 142, in handle_event
File "mitmproxy/proxy/layer.py", line 240, in __continue
File "mitmproxy/proxy/layer.py", line 196, in __process
File "mitmproxy/proxy/layers/quic/_stream_layers.py", line 91, in _handle_event
File "mitmproxy/proxy/tunnel.py", line 83, in _handle_event
File "mitmproxy/proxy/layers/quic/_stream_layers.py", line 321, in receive_data
File "mitmproxy/proxy/layers/quic/_stream_layers.py", line 175, in tls_interact
File "aioquic/quic/connection.py", line 536, in datagrams_to_send
IndexError: list index out of range
[10:52:54.052][10.0.115.19:0] client disconnect
[10:52:54.053][10.0.115.19:0] Server QUIC handshake failed. connection closed
I am afraid I don't know what site this is on, or what the traffic is. I am happy to investigate further if it would be helpful
❯ mitmproxy --version
Mitmproxy: 12.2.1 binary
Python: 3.14.0
OpenSSL: OpenSSL 3.5.4 30 Sep 2025
Platform: macOS-26.0-arm64-arm-64bit-Mach-O
Problem Description
I'm running in local mode on my Mac, so there is a lot of traffic going across the wire.
I am afraid I don't know what site this is on, or what the traffic is. I am happy to investigate further if it would be helpful
System Information
Checklist