CVE-2026-64572 ipv4: fib: free fib_alias with kfree_rcu() on insert error path
A use-after-free in the Linux kernel IPv4 FIB allows local attackers with CAP_NET_ADMIN to cause a crash or potentially execute code.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-64572?
CVE-2026-64572 is an use after free vulnerability in Linux, published on 5 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
ipv4: fib: free fib_alias with kfree_rcu() on insert error path
fib_table_insert() publishes new_fa into the leaf's fa_list with fib_insert_alias() before calling the fib entry notifiers. When a notifier fails, the error path removes new_fa with fib_remove_alias() (hlist_del_rcu) and frees it right away with kmem_cache_free().
fib_table_lookup() walks that list under rcu_read_lock() only, so a concurrent lookup that already reached new_fa keeps reading it after the free:
BUG: KASAN: slab-use-after-free in fib_table_lookup (net/ipv4/fib_trie.c:1601) Read of size 1 at addr ffff88810676d4eb by task exploit/297 Call Trace: fib_table_lookup (net/ipv4/fib_trie.c:1601) ip_route_output_key_hash_rcu (net/ipv4/route.c:2814) ip_route_output_key_hash (net/ipv4/route.c:2705) __ip4_datagram_connect (net/ipv4/datagram.c:49) udp_connect (net/ipv4/udp.c:2144) __sys_connect (net/socket.c:2167) __x64_sys_connect (net/socket.c:2173) do_syscall_64 entry_SYSCALL_64_after_hwframe which belongs to the cache ip_fib_alias of size 56
Triggering the error path needs CAP_NET_ADMIN and a registered fib notifier that can reject a route; a netdevsim device whose IPv4 FIB resource is exhausted is enough.
Free new_fa with alias_free_mem_rcu(), as fib_table_delete() already does for a fib_alias removed from the trie.
Which versions are affected by CVE-2026-64572?
How do I fix CVE-2026-64572?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-64572 being exploited?
There is no known exploitation of CVE-2026-64572 in the wild and no public exploit code.
Sources
Also known as AZL-94473, BELL-CVE-2026-64572, DEBIAN-CVE-2026-64572, GHSA-q235-77fh-m2c6, UBUNTU-CVE-2026-64572.