diff -ru libz-1.2.8.2015.12.26.orig/inflate.c libz-1.2.8.2015.12.26/inflate.c
--- libz-1.2.8.2015.12.26.orig/inflate.c	2015-12-21 23:37:02.000000000 +0100
+++ libz-1.2.8.2015.12.26/inflate.c	2022-10-27 11:32:39.403516533 +0200
@@ -595,8 +595,9 @@
                 if (copy > have) copy = have;
                 if (copy) {
                     if (state->head != NULL &&
-                        state->head->extra != NULL) {
-                        len = state->head->extra_len - state->length;
+                        state->head->extra != NULL &&
+                        (len = state->head->extra_max - state->length) <
+                            state->head->extra_max) {
                         memcpy(state->head->extra + len, next,
                                len + copy > state->head->extra_max ?
                                state->head->extra_max - len : copy);