<p><b>@miri64</b> commented on this pull request.</p>

<hr>

<p>In <a href="https://github.com/RIOT-OS/RIOT/pull/11773#discussion_r299984885">sys/net/gnrc/application_layer/tftp/gnrc_tftp.c</a>:</p>
<pre style='color:#555'>> @@ -405,11 +405,14 @@ int gnrc_tftp_server(tftp_data_cb_t data_cb, tftp_start_cb_t start_cb, tftp_stop
     }
 
     /* context will be initialized when a connection is established */
-    tftp_context_t ctxt;
-    ctxt.data_cb = data_cb;
-    ctxt.start_cb = start_cb;
-    ctxt.stop_cb = stop_cb;
-    ctxt.enable_options = use_options;
+    tftp_context_t ctxt = {
+        .dst_port = GNRC_TFTP_DEFAULT_DST_PORT,
+        .src_port = GNRC_TFTP_DEFAULT_DST_PORT,
</pre>
<p>Wait no, right. I moved the initialization to <a class="commit-link" data-hovercard-type="commit" data-hovercard-url="https://github.com/RIOT-OS/RIOT/commit/2fce0950bf0d03a2702bba7312fa55119e70a085/hovercard" href="https://github.com/RIOT-OS/RIOT/commit/2fce0950bf0d03a2702bba7312fa55119e70a085"><tt>2fce095</tt></a>, as <code>_tftp_state_processes</code> relied on certain configurations of <code>ctxt->dst_port</code> I was unsure about. I tested it with your crafted input, and it did not crash (the server was not responding anymore, because a legal input changed its port...., see <a class="issue-link js-issue-link" data-error-text="Failed to load issue title" data-id="463735214" data-permission-text="Issue title is private" data-url="https://github.com/RIOT-OS/RIOT/issues/11778" data-hovercard-type="pull_request" data-hovercard-url="/RIOT-OS/RIOT/pull/11778/hovercard" href="https://github.com/RIOT-OS/RIOT/pull/11778">#11778</a>).</p>

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