Bug 2401550 (CVE-2023-53566)

Summary: CVE-2023-53566 kernel: netfilter: nft_set_rbtree: fix null deref on element insertion
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in the Netfilter subsystem in the Linux kernel. A NULL pointer dereference and a use-after-free issue can be triggered due to an improper check and an improper way of iterating a red-black tree during garbage collector operations, potentially resulting in a denial of service and possibly privilege escalation.
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Description OSIDB Bzimport 2025-10-04 16:06:56 UTC 
In the Linux kernel, the following vulnerability has been resolved:

netfilter: nft_set_rbtree: fix null deref on element insertion

There is no guarantee that rb_prev() will not return NULL in nft_rbtree_gc_elem():

general protection fault, probably for non-canonical address 0xdffffc0000000003: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000018-0x000000000000001f]
 nft_add_set_elem+0x14b0/0x2990
  nf_tables_newsetelem+0x528/0xb30

Furthermore, there is a possible use-after-free while iterating,
'node' can be free'd so we need to cache the next value to use.
Comment 1 Alexander B 2025-10-06 12:28:16 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025100451-CVE-2023-53566-1c57@gregkh/T