[stunnel-users] Odd stunnel problem

[Tristan Schmelcher]

My company uses stunnel on a telecom product and we have run into a strange
problem. One of our customers sees an issue every couple weeks where the
stunnel process becomes busted. Attempts to establish a connection through
stunnel to any host hang indefinitely. Interface stats indicate that stunnel
sends and receives a flurry of packets--as if a TLS connection was
successfully established--but the local plaintext socket connection to
stunnel never passes data. For example, if attempting to run telnet over
stunnel, the telnet client just sits there and doesn't write anything to the
terminal. During this time the network is otherwise functioning fine.

Unfortunately nothing is logged by stunnel when this happens and we haven't
been able to reproduce the problem in a controlled environment. Does anyone
have any ideas what might be happening?

We currently use stunnel 4.35 with debug = warning, sslVersion = TLSv1, and
verify = 2.
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