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<a href="https://gitlab.com/asosedkin">Alexander Sosedkin</a>
<a href="https://gitlab.com/gnutls/gnutls/-/issues/1739#note_2763354889">commented</a>:
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<p style="color: inherit; line-height: 1.5; margin: 0;">We think that the remote's closing its sending side of the TCP connection without using some sort of a TLS message (an alert?) beforehand that it's about to do so, somehow upsets GNUTLS.</p>
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<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">A solid hypothesis, if only there was some quick way to check it...</p>
<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">TLS 1.3 specification section titled "Closure Alerts" is here: <a href="https://datatracker.ietf.org/doc/html/rfc8446#section-6.1" rel="nofollow noreferrer noopener" target="_blank" style="margin-top: 0;">https://datatracker.ietf.org/doc/html/rfc8446#section-6.1</a>,
and here's one for TLS 1.2: <a href="https://datatracker.ietf.org/doc/html/rfc5246#section-7.2.1" rel="nofollow noreferrer noopener" target="_blank">https://datatracker.ietf.org/doc/html/rfc5246#section-7.2.1</a>, trivially reachable from <a href="https://security.stackexchange.com/questions/82028/ssl-tls-is-a-server-always-required-to-respond-to-a-close-notify" rel="nofollow noreferrer noopener" target="_blank">what I get as the first google result for "how are tls connections closed"</a>.</p>
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<p style="color: inherit; line-height: 1.5; margin: 0 0 1rem;">The client and the server must share knowledge that the connection is
ending in order to avoid a truncation attack.</p>
<p style="color: inherit; line-height: 1.5; margin: 0 0 1rem;">...</p>
<p style="color: inherit; line-height: 1.5; margin: 0;">Each party MUST send a "close_notify" alert before closing its write
side of the connection, unless it has already sent some error alert.</p>
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<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">Case closed.</p>
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<p style="color: inherit; line-height: 1.5; margin: 0;">But we don't know much about the intricacies of TLS and would really appreciate if you could take a look as to why GNUTLS can't handle the request above.</p>
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<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">It can. It'll then rightfully report the insecure protocol violation by the other peer to whatever code is using gnutls.</p>
<p dir="auto" style="color: #3a383f; margin: 0;" align="initial">The gnutls support mailing list is <a href="https://lists.gnutls.org/mailman/listinfo/gnutls-help" rel="nofollow noreferrer noopener" target="_blank" style="margin-top: 0;">gnutls-help@lists.gnutls.org</a>. This is a bugtracker for issues in gnutls, and nothing in your report suggests gnutls misbehaving.</p>
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