Bug 2511413 (CVE-2026-64572)

Summary: CVE-2026-64572 kernel: ipv4: fib: free fib_alias with kfree_rcu() on insert error path
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's IPv4 forwarding information base (FIB) component. A local attacker with administrative network capabilities (CAP_NET_ADMIN) could exploit a timing issue during route insertion and lookup operations. This could lead to a "use-after-free" vulnerability, where the system attempts to access memory that has already been released. The most important consequence is a denial of service, potentially causing system instability or crashes.
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Description OSIDB Bzimport 2026-08-05 09:02:22 UTC 
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.
Comment 1 gkamathe 2026-08-06 10:40:43 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026080559-CVE-2026-64572-e260@gregkh/T