diff --git a/sys/cpu/x86_64/misc/x86_64-gdbstub.c b/sys/cpu/x86_64/misc/x86_64-gdbstub.c
--- a/sys/cpu/x86_64/misc/x86_64-gdbstub.c
+++ b/sys/cpu/x86_64/misc/x86_64-gdbstub.c
@@ -585,6 +585,8 @@
 	      && *(ptr++) == ','
 	      && hexToInt (&ptr, &length))
 	    {
+	      if (length < 0 || length > BUFMAX/2)
+		length = BUFMAX/2;
 	      if (mem2hex((vm_offset_t) addr, remcomOutBuffer, length) == NULL)
 		strcpy (remcomOutBuffer, "E03");
 	      break;