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<a href="https://gitlab.com/SmallTown123">SmallTown123</a> created an issue: <a href="https://gitlab.com/gnutls/gnutls/-/issues/1439">#1439</a>
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<p dir="auto" style="color: #333238; margin: 0;" align="initial">When testing multiple versions of GnuTLS（3.6.12,3.6.4,3.5.18,but this seems to be common across all versions of GnuTLS）,
we found that the GnuTLS server did not detect the payload of the <strong style="font-weight: bold; margin-top: 0;">ChangeCipherSpec</strong> protocol during the third handshake test of TLS1.2.
Its normal payload value should be 1 (according to RFC5246).
The GnuTLS server still had a normal response and did not response any Alert messages while we sent other random payload bytes.
At present, this issue does not cause a direct security issue, but it is easy to cause parsing ambiguity in the communication process, and it is unknown whether it will be exploited in the future.
I think the code snippet that caused the issue is located at <code style='font-size: 90%; color: #1f1e24; word-wrap: break-word; background-color: #ececef; border-radius: 4px; font-weight: inherit; font-family: var(--default-mono-font, "Menlo"),"DejaVu Sans Mono","Liberation Mono","Consolas","Ubuntu Mono","Courier New","andale mono","lucida console",monospace; white-space: pre-wrap; overflow-wrap: break-word; word-break: keep-all; padding: 2px 4px;'>static int recv_handshake_final(gnutls_session_t session, int init)</code>
function in ./lib/handshake.c.</p>
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