In the Linux kernel, the following vulnerability has been resolved:

net/sched: act ct: fix helper UAF due to extensions realloc

While calling the helpers, a raw pointer to the extensions area is wired into expectations list:

-> nf ct helper() -> helper->help() -> nf ct expect related report() -> nf ct expect insert() -> hlist add head rcu(&exp->lnode, &master help->expectations)

In case the connection is not confirmed yet, more extensions can be added afterwards with * ext add() calls reallocating the extension space and leaving the now invalid pointer in the expectations list that is later accessed while removing the expectation.

Make sure that helpers are called at the end after all the other extensions are already added.

Note that the helper rejection now leaves the mark and labels set, but that's not different from how the NAT was handled before or how the mark and the labels were handled on confirmation failure. And there are no atomicity guarantees provided by the API anyway.