--- telnetd/slc.c.orig	2026-03-26 22:18:55.633752584 -0300
+++ telnetd/slc.c	2026-03-26 22:17:33.771648092 -0300
@@ -162,6 +162,11 @@
 void
 add_slc (char func, char flag, cc_t val)
 {
+  if (slcptr + 6 >= slcbuf + sizeof (slcbuf))
+    {
+      return;
+    }
+
   if ((*slcptr++ = (unsigned char) func) == 0xff)
     *slcptr++ = 0xff;