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

netfilter: nf_conncount: Fully initialize struct nf_conncount_tuple in insert_tree()

Since commit b36e4523d4d5 ("netfilter: nf_conncount: fix garbage
collection confirm race"), cpu and jiffies32 were introduced to
the struct nf_conncount_tuple.

The commit made nf_conncount_add() initialize conn->cpu and
conn->jiffies32 when allocating the struct.
In contrast, count_tree() was not changed to initialize them.

By commit 34848d5c896e ("netfilter: nf_conncount: Split insert and
traversal"), count_tree() was split and the relevant allocation
code now resides in insert_tree().
Initialize conn->cpu and conn->jiffies32 in insert_tree().

BUG: KMSAN: uninit-value in find_or_evict net/netfilter/nf_conncount.c:117 [inline]
BUG: KMSAN: uninit-value in __nf_conncount_add+0xd9c/0x2850 net/netfilter/nf_conncount.c:143
find_or_evict net/netfilter/nf_conncount.c:117 [inline]
__nf_conncount_add+0xd9c/0x2850 net/netfilter/nf_conncount.c:143
count_tree net/netfilter/nf_conncount.c:438 [inline]
nf_conncount_count+0x82f/0x1e80 net/netfilter/nf_conncount.c:521
connlimit_mt+0x7f6/0xbd0 net/netfilter/xt_connlimit.c:72
__nft_match_eval net/netfilter/nft_compat.c:403 [inline]
nft_match_eval+0x1a5/0x300 net/netfilter/nft_compat.c:433
expr_call_ops_eval net/netfilter/nf_tables_core.c:240 [inline]
nft_do_chain+0x426/0x2290 net/netfilter/nf_tables_core.c:288
nft_do_chain_ipv4+0x1a5/0x230 net/netfilter/nft_chain_filter.c:23
nf_hook_entry_hookfn include/linux/netfilter.h:154 [inline]
nf_hook_slow+0xf4/0x400 net/netfilter/core.c:626
nf_hook_slow_list+0x24d/0x860 net/netfilter/core.c:663
NF_HOOK_LIST include/linux/netfilter.h:350 [inline]
ip_sublist_rcv+0x17b7/0x17f0 net/ipv4/ip_input.c:633
ip_list_rcv+0x9ef/0xa40 net/ipv4/ip_input.c:669
__netif_receive_skb_list_ptype net/core/dev.c:5936 [inline]
__netif_receive_skb_list_core+0x15c5/0x1670 net/core/dev.c:5983
__netif_receive_skb_list net/core/dev.c:6035 [inline]
netif_receive_skb_list_internal+0x1085/0x1700 net/core/dev.c:6126
netif_receive_skb_list+0x5a/0x460 net/core/dev.c:6178
xdp_recv_frames net/bpf/test_run.c:280 [inline]
xdp_test_run_batch net/bpf/test_run.c:361 [inline]
bpf_test_run_xdp_live+0x2e86/0x3480 net/bpf/test_run.c:390
bpf_prog_test_run_xdp+0xf1d/0x1ae0 net/bpf/test_run.c:1316
bpf_prog_test_run+0x5e5/0xa30 kernel/bpf/syscall.c:4407
__sys_bpf+0x6aa/0xd90 kernel/bpf/syscall.c:5813
__do_sys_bpf kernel/bpf/syscall.c:5902 [inline]
__se_sys_bpf kernel/bpf/syscall.c:5900 [inline]
__ia32_sys_bpf+0xa0/0xe0 kernel/bpf/syscall.c:5900
ia32_sys_call+0x394d/0x4180 arch/x86/include/generated/asm/syscalls_32.h:358
do_syscall_32_irqs_on arch/x86/entry/common.c:165 [inline]
__do_fast_syscall_32+0xb0/0x110 arch/x86/entry/common.c:387
do_fast_syscall_32+0x38/0x80 arch/x86/entry/common.c:412
do_SYSENTER_32+0x1f/0x30 arch/x86/entry/common.c:450
entry_SYSENTER_compat_after_hwframe+0x84/0x8e

Uninit was created at:
slab_post_alloc_hook mm/slub.c:4121 [inline]
slab_alloc_node mm/slub.c:4164 [inline]
kmem_cache_alloc_noprof+0x915/0xe10 mm/slub.c:4171
insert_tree net/netfilter/nf_conncount.c:372 [inline]
count_tree net/netfilter/nf_conncount.c:450 [inline]
nf_conncount_count+0x1415/0x1e80 net/netfilter/nf_conncount.c:521
connlimit_mt+0x7f6/0xbd0 net/netfilter/xt_connlimit.c:72
__nft_match_eval net/netfilter/nft_compat.c:403 [inline]
nft_match_eval+0x1a5/0x300 net/netfilter/nft_compat.c:433
expr_call_ops_eval net/netfilter/nf_tables_core.c:240 [inline]
nft_do_chain+0x426/0x2290 net/netfilter/nf_tables_core.c:288
nft_do_chain_ipv4+0x1a5/0x230 net/netfilter/nft_chain_filter.c:23
nf_hook_entry_hookfn include/linux/netfilter.h:154 [inline]
nf_hook_slow+0xf4/0x400 net/netfilter/core.c:626
nf_hook_slow_list+0x24d/0x860 net/netfilter/core.c:663
NF_HOOK_LIST include/linux/netfilter.h:350 [inline]
ip_sublist_rcv+0x17b7/0x17f0 net/ipv4/ip_input.c:633
ip_list_rcv+0x9ef/0xa40 net/ip
---truncated---

References

• https://nvd.nist.gov/vuln/detail/CVE-2025-21959
• https://git.kernel.org/stable/c/2db5baaf047a7c8d6ed5e2cc657b7854e155b7fc
• https://git.kernel.org/stable/c/a62a25c6ad58fae997f48a0749afeda1c252ae51
• https://git.kernel.org/stable/c/d653bfeb07ebb3499c403404c21ac58a16531607
• https://git.kernel.org/stable/c/db1e0c0856821c59a32ea3af79476bf20a6beeb2
• https://git.kernel.org/stable/c/fda50302a13701d47fbe01e1739c7a51114144fb
• https://git.kernel.org/stable/c/2a154ce766b995494e88d8d117fa82cc6b73dd87
• https://git.kernel.org/stable/c/e8544a5a97bee3674e7cd6bf0f3a4af517fa9146
• https://git.kernel.org/stable/c/f522229c5563b59b4240261e406779bba6754159