Use-after-free in Linux kernel nf_conntrack_helper expectation cleanup
CVE-2026-43027 is a Linux kernel netfilter vulnerability in the nf_conntrack_helper expectation cleanup path. When nf_conntrack_helper_unregister() invokes nf_ct_expect_iterate_destroy() during helper unregistration, it incorrectly passes NULL instead of the helper pointer as the iterator data argument. As a result, expect_iter_me() does not match and destroy expectations associated with the helper being unregistered. Those stale expectations survive cleanup, and after unregister returns, nfnl_cthelper_del() frees the helper object. Later, expectation dump paths or packet-driven init_conntrack() processing can dereference exp->helper, which now points to freed memory, resulting in a slab use-after-free. The provided KASAN trace shows the fault during expectation display via exp_seq_show() and seq_read_iter(), confirming dereference of freed helper-backed data.
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