On Monday, May 12, 2025 at 03:39:46 AM EDT, Peter Pentchev <roam@ringlet.net> wrote:
On Sun, May 11, 2025 at 09:02:15PM -0000, lynn9a--- via stunnel-users wrote:
> Hi, All
> When we try to start stunnel(stunnel 5.67, wolfSSL5.6.4 on linux), there is an error randomly happened like following, anybody knows why this happen and how to fix this?
> Thanks
The "peer suddenly disconnected" message most probably means that:
- something established a connection to your stunnel service
- stunnel started preparing to process that connection
- the other side disconnected immediately, before sending or receiving any data
IMHO, these are the two most probable reasons for that to happen:
- if it is indeed random, perhaps it is the result of somebody (or many somebodies)
running port scans either on your server specifically, or on a whole range of
IP addresses and ports, and recording somewhere what is running on which host and
which port
- if it is more or less periodical, it might be some monitoring system somewhere
that is set up to check whether there is anything listening on that
address and port; for more of my thoughts on this, of which I'm sure some people
on this list have had enough, see my answer in this thread:
https://www.stunnel.org/mailman3/hyperkitty/list/stunnel-users@stunnel.org/thread/GQ3U2LHNTJOHBWIG34SHUU5FGURON7BO/ (TL;DR: merely checking whether something accepts a TCP connection is not
enough for a health check on the service itsef, and it can lead to confusion
for people looking at the logs, as in your case)
Hope that helps at least a bit!
G'luck,
Peter
--
Peter Pentchev
roam@ringlet.net roam@debian.org peter@morpheusly.comPGP key:
https://www.ringlet.net/roam/roam.key.ascKey fingerprint 2EE7 A7A5 17FC 124C F115 C354 651E EFB0 2527 DF13
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